General Description
The MAX5098A is a dual-output, high-switching-frequen-
cy DC-DC converter with integrated n-channel switches
that can be used either in high-side or low-side configura-
tion. Each output can be configured either as a buck con-
verter or a boost converter. In the buck configuration, this
device delivers up to 2A from converter 1 and 1A from
converter 2. The MAX5098A also integrates a load-dump
protection circuitry that is capable of handling load-dump
transients up to 80V for automotive applications. The
load-dump protection circuit utilizes an internal charge-
pump to drive the gate of an external n-channel MOSFET.
When an overvoltage or load-dump condition occurs, the
series protection MOSFET absorbs the high voltage tran-
sient to prevent damage to lower voltage components.
The DC-DC converters operate over a wide operating
voltage range from 4.5V to 19V. The MAX5098A oper-
ates 180° out-of-phase with an adjustable switching fre-
quency to minimize external components while allowing
the ability to make trade-offs between the size, efficiency,
and cost. The high switching frequency (up to 2.2MHz)
also allows this device to operate outside the AM band
for automotive applications.
This device utilizes voltage-mode control for stable oper-
ation and external compensation, thus the loop gain is
tailored to optimize component selection and transient
response. This device can be synchronized to an exter-
nal clock fed at the SYNC input. Also, a clock output
(CKO) allows a master-slave connection of two devices
with a four-phase synchronized switching sequence.
Additional features include internal digital soft-start, indi-
vidual enable for each DC-DC regulator (EN1 and EN2),
open-drain power-good outputs (PGOOD1 and
PGOOD2), and a shutdown input (ON/OFF).
Other features of the MAX5098A include overvoltage pro-
tection, short-circuit (hiccup current limit) and thermal
protection. The MAX5098A is available in a thermally
enhanced, exposed pad, 5mm x 5mm, 32-pin TQFN
package and is fully specified over the automotive
-40°C to +125°C temperature range.
Applications
Automotive AM/FM Radio Power Supply
Automotive Instrument Cluster Display
Features
oWide 4.5V to 5.5V or 5.2V to 19V Input Voltage
Range (with Up to 80V Load-Dump Protection)
oDual-Output DC-DC Converter with Integrated
Power MOSFETs
oEach Output Configurable in Buck or Boost Mode
oAdjustable Outputs from 0.8V to 0.85VIN Buck
Configuration) and from VIN to 28V (Boost
Configuration)
oIOUT1 and IOUT2 of 2A and 1A (Respectively) in
Buck Configuration
oSwitching Frequency Programmable from 200kHz
to 2.2MHz
oSynchronization Input (SYNC)
oClock Output (CKO) for Four-Phase Master-Slave
Operation
oIndividual Converter Enable Input and Power-
Good Output
oLow-IQ(7µA) Standby Current (ON/OFF)
oInternal Digital Soft-Start and Soft-Stop
oShort-Circuit Protection on Outputs and
Maximum Duty-Cycle Limit
oOvervoltage Protection on Outputs with Auto
Restart
oThermal Shutdown
oThermally Enhanced 32-Pin TQFN Package
Dissipates up to 2.7W at +70°C
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-4111; Rev 0; 5/08
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Pin Configuration appears at end of data sheet
EVALUATION KIT
AVAILABLE
+
Denotes a lead-free package.
*
EP = Exposed pad.
PART TEMP RANGE PIN-PACKAGE
MAX5098AATJ+
-40°C to +125°C 32 TQFN-EP*
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDRV = VL, V+ = VL= IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND_ = SGND,
CBYPASS = 0.22µF (low ESR), CVL = 4.7µF (ceramic), CV+ = 1µF (low ESR), CIN_HIGH = 1µF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ,
TJ= -40°C to +125°C, unless otherwise noted.) (Note 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1: Package thermal resistances were obtained using the method described in JEDEC specifications. For detailed information
on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
V+ to SGND............................................................-0.3V to +25V
V+ to IN_HIGH...........................................................-19V to +6V
IN_HIGH to SGND ..................................................-0.3V to +19V
IN_HIGH Maximum Input Current .......................................60mA
BYPASS to SGND..................................................-0.3V to +2.5V
GATE to V+.............................................................-0.3V to +12V
GATE to SGND .......................................................-0.3V to +36V
SGND to PGND_ ...................................................-0.3V to +0.3V
VLto SGND..................-0.3V to the Lower of +6V or (V+ + 0.3V)
VDRV to SGND .........................................................-0.3V to +6V
BST1/VDD1, BST2/VDD2, DRAIN_,
PGOOD_ to SGND ..............................................-0.3V to +30V
ON/OFF to SGND ...............................-0.3V to (IN_HIGH + 0.3V)
BST1/VDD1 to SOURCE1,
BST2/VDD2 to SOURCE2......................................-0.3V to +6V
SOURCE_ to SGND................................................-0.6V to +25V
SOURCE_ to PGND_.................................................-1V for 50ns
EN_ to SGND............................................................-0.3V to +6V
OSC, FSEL_1, COMP_, SYNC,
FB_ to SGND..............................................-0.3V to (VL+ 0.3V)
CKO to SGND..........................................-0.3V to (VDRV + 0.3V)
SOURCE1, DRAIN1 Peak Current ..............................5A for 1ms
SOURCE2, DRAIN2 Peak Current ..............................3A for 1ms
VL, BYPASS to
SGND Short Circuit ................... Continuous, Internally Limited
Continuous Power Dissipation (TA= +70°C)
32-Pin TQFN-EP (derate 34.5mW/°C above +70°C)..2759mW
Package Junction-to-Ambient
Thermal Resistance (θJA) (Note 1).............................29.0°C/W
Package Junction-to-Case
Thermal Resistance (θJC) (Note 1) ..............................1.7°C/W
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range ............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) ................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SYSTEM SPECIFICATIONS
V+ = IN_HIGH 5.2 19
Input Voltage Range V+ VL = V+ = IN_HIGH (Note 3) 4.5 5.5 V
V+ Operating Supply Current IQVL unloaded, no switching 4.2 mA
V+ Standby Supply Current IV+STBY VEN_ = 0V, PGOOD_ unconnected, V+ =
VIN_HIGH = 14V 0.75 1.1 mA
V+ = VL = 5.2V 78
V+ = 12V 76
Efficiency η
(VOUT1 = 5V at 1.5A,
VOUT2 = 3.3V at 0.75A,
fSW = 1.85MHz V+ = 16V 70
%
OVERVOLTAGE PROTECTOR
IN_HIGH Clamp Voltage IN_HIGH ISINK = 10mA 19 20 21 V
IN_HIGH Clamp Load
Regulation 1mA < ISINK < 50mA 160 mV
IN_HIGH Supply Current IIN_HIGH VEN_ = VPGOOD_ = VGATE = 0V,
VIN_HIGH = VON/OFF = 14V 270 600 µA
IN_HIGH Standby Supply
Current IIN_HIGHSTBY
VON/OFF = 0V , P GOOD _ = V + =
unconnected, VIN_HIGH = 14V , TA = -40°C
to +85°C
79µA
V+ to IN_HIGH Overvoltage
Clamp VOV VOV = V+ - VIN_HIGH, IGATE = 0mA
(sinking) 1.2 1.85 2.5 V
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
_______________________________________________________________________________________ 3
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Rising, ON/OFF = IN_HIGH, GATE rising 3.6 4.1
IN_HIGH Startup Voltage IN_HIGH
UVLO Falling, ON/OFF = IN_HIGH, GATE falling 3.45 V
GATE Charge Current IGATE_CH VIN_HIGH = VON/OFF = 14V,
VGATE = V+ = 0V 20 45 80 µA
V+ = VIN_HIGH = VON/OFF = 4.5V,
IGATE = 1µA, sourcing 4.0 5.3 7.5
GATE Output Voltage VGATE -
VIN_HIGH V+ = VIN_HIGH = VON/OFF = 14V,
IGATE = 1µA, sourcing 9
V
GATE Turn-Off Pulldown
Current IGATE_PD VIN_HIGH = 14V, VON/OFF = 0V, V+ = 0V,
VGATE = 5V, sinking 3.6 mA
STARTUP/VL REGULATOR
VL Undervoltage Lockout Trip
Level UVLO VL falling 3.9 4.1 4.3 V
VL Undervoltage Lockout
Hysteresis 180 mV
VL Output Voltage VLISOURCE_ = 0 to 40mA, 5.5V ≤ V+ ≤ 19V 5.0 5.2 5.5 V
VL LDO Short-Circuit Current IVL_SHORT V+ = VIN_HIGH = 5.2V 130 mA
VL LDO Dropout Voltage VLDO ISOURCE_ = 40mA, V+ = VIN_HIGH = 4.5V 300 550 mV
BYPASS OUTPUT
BYPASS Voltage VBYPASS IBYPASS = 0µA 1.98 2.00 2.02 V
BYPASS Load Regulation ΔVBYPASS 0 < IBYPASS < 100µA (sourcing) 2 5 mV
SOFT-START/SOFT-STOP
Digital Ramp Period Soft-
Start/Soft-Stop Internal 6-bit DAC 2048
fSW
Clock
Cycles
Soft-Start/Soft-Stop 64 Steps
VOLTAGE-ERROR AMPLIFIER
FB_ Input Bias Current IFB_ 250 nA
-40°C ≤ TA ≤ +85°C 0.783 0.8 0.809
FB_ Input Voltage Set Point VFB_ -40°C ≤ TA ≤ +125°C 0.785 0.814 V
FB_ to COMP_
Transconductance gM1.4 2.4 3.4 mS
INTERNAL MOSFETS
ISWITCH = 100mA, BST1/VDD1 to
VSOURCE1 = 5.2V 195
On-Resistance High-Side
MOSFET Converter 1 RON1 ISWITCH = 100mA, BST1/VDD1 to
VSOURCE1 = 4.5V 208 355
mΩ
ELECTRICAL CHARACTERISTICS (continued)
(VDRV = VL, V+ = VL= IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND_ = SGND,
CBYPASS = 0.22µF (low ESR), CVL = 4.7µF (ceramic), CV+ = 1µF (low ESR), CIN_HIGH = 1µF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ,
TJ= -40°C to +125°C, unless otherwise noted.) (Note 2)
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VDRV = VL, V+ = VL= IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND_ = SGND,
CBYPASS = 0.22µF (low ESR), CVL = 4.7µF (ceramic), CV+ = 1µF (low ESR), CIN_HIGH = 1µF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ,
TJ= -40°C to +125°C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
ISWITCH = 100mA, BST2/VDD2 to
VSOURCE2 = 5.2V 280
On-Resistance High-Side
MOSFET Converter 2 RON2 ISWITCH = 100mA, BST2/VDD2 to
VSOURCE2 = 4.5V 300 520
mΩ
Minimum Converter 1 Output
Current IOUT1 VOUT1 = 5V, V+ = 12V (Note 4) 2 A
Minimum Converter 2 Output
Current IOUT2 VOUT2 = 3.3V, V+ = 12V (Note 4) 1 A
Converter 1/Converter 2
MOSFET DRAIN_ Leakage
Current
ILK12 VEN1 = VEN2 = 0V, VDRAIN_ = 19V,
VSOURCE_ = 0V 20 µA
Internal Weak Low-Side Switch
On-Resistance RONLSSW_ ILSSW = 30mA 22 Ω
INTERNAL SWITCH CURRENT LIMIT
Internal Switch Current-Limit
Converter 1 ICL1 V+ = VIN_HIGH = 5.2V, VL = VDRV =
VBST_/VDD_ = 5.2V 2.8 3.45 4.3 A
Internal Switch Current-Limit
Converter 2 ICL2 V+ = VIN_HIGH = 5.2V, VL = VDRV =
VBST_/VDD_ = 5.2V 1.75 2.1 2.6 A
SWITCHING FREQUENCY
PWM Maximum Duty Cycle DMAX SYNC = SGND, fSW = 1.25MHz 82 90 95 %
Switching Frequency Range fSW 200 2200 kHz
Switching Frequency fSW ROSC = 6.81kΩ, each converter
(FSEL_1 = VL)1.7 1.9 2.1 MHz
5.6kΩ < ROSC < 10kΩ, 1% 5
Switching Frequency Accuracy 10kΩ < ROSC < 62.5kΩ, 1% 7 %
SYNC Frequency Range fSYNC
SYNC input frequency is twice the
individual converter frequency,
FSEL_1 = VL (see the Setting the
Switching Frequency section)
400 4400 kHz
SYNC High Threshold VSYNCH 2V
SYNC Low Threshold VSYNCL 0.8 V
SYNC Input Leakage ISYNC_LEAK 2µA
SYNC Input Minimum Pulse
Width tSYNCIN 100 ns
Clock Output Phase Delay CKOPHASE ROSC = 62.5kΩ, with respect to converter
2/SOURCE2 waveform 40 D eg r ees
SYNC to Source 1 Phase Delay SYNCPHASE ROSC = 62.5kΩ90 D eg r ees
Clock Output High Level VCKOH VL = 5.2V, sourcing 5mA 3.6 V
Clock Output Low Level VCKOL VL = 5.2V, sinking 5mA 0.6 V
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VDRV = VL, V+ = VL= IN_HIGH = 5.2V or V+ = IN_HIGH = 5.2V to 19V, EN_ = VL, SYNC = GND, IVL = 0mA, PGND_ = SGND,
CBYPASS = 0.22µF (low ESR), CVL = 4.7µF (ceramic), CV+ = 1µF (low ESR), CIN_HIGH = 1µF (ceramic), RIN_HIGH = 3.9kΩ, ROSC = 10kΩ,
TJ= -40°C to +125°C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
FSEL_1
FSEL_1 Input High Threshold VIH 2V
FSEL_1 Input Low Threshold VIL 0.8 V
FSEL_1 Input Leakage IFSEL_1_LEAK 2µA
ON/OFF
ON/OFF Input High Threshold VIH 2V
ON/OFF Input Low Threshold VIL 0.8 V
ON/OFF Input Leakage Current ION/OFF_LEAK VON/OFF = 5V 0.26 2.00 µA
EN_ INPUTS
EN_ Input High Threshold VIH EN_ rising 1.9 2.0 2.1 V
EN_ Input Hysteresis VEN_HYS 0.5 V
EN_ Input Leakage Current IEN_LEAK -1 +1 µA
POWER-GOOD OUTPUT (PGOOD1, PGOOD2)
PGOOD_ Threshold VTPGOOD_ Falling 90 92.5 95 % VFB_
PGOOD_ Output Voltage VPGOOD_ ISINK = 3mA 0.4 V
PGOOD_ Output Leakage
Current ILKPGOOD_ V+ = VL = VIN_HIGH = VEN_ = 5.2V,
VPGOOD_ = 23V, VFB_ = 1V 2µA
OUTPUT OVERVOLTAGE PROTECTION
FB_ OVP Threshold Rising VOVP_R 107 114 121 % VFB_
FB_ OVP Threshold Falling VOVP_F 12.5 V
THERMAL PROTECTION
Thermal Shutdown TSHDN Rising +165 °C
Thermal Hysteresis THYST 20 °C
Note 2: 100% tested at TA= +25°C and TA= +125°C. Specifications at TA= -40°C are guaranteed by design and not production
tested.
Note 3: Operating supply range (V+) is guaranteed by VLline regulation test. Connect V+ to IN_HIGH and VLfor 5V operation.
Note 4: Output current is limited by the power dissipation of the package; see the
Power Dissipation
section in the
Applications
Information
section.
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
6 _______________________________________________________________________________________
Typical Operating Characteristics
(See the
Typical Application Circuit
, unless otherwise noted. V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means
that N1 is shorted externally.)
OUTPUT1 EFFICIENCY
vs. LOAD CURRENT
MAX5098A toc01
LOAD (A)
OUTPUT1 EFFICIENCY (%)
1.81.61.2 1.40.6 0.8 1.00.4
10
20
30
40
50
60
70
80
90
100
0
0.2 2.0
VIN = 8V
VIN = 14V VIN = 16V
VOUT = 5V
fSW = 1.85MHz
OUTPUT2 EFFICIENCY
vs. LOAD CURRENT
MAX5098A toc02
LOAD (A)
OUTPUT2 EFFICIENCY (%)
0.90.80.6 0.70.4 0.50.30.2 1.0
10
20
30
40
50
60
70
80
90
100
0
VIN = 16V
VIN = 8V VIN = 14V
VIN = 5.5V
VIN = 4.5V
VOUT = 3.3V
fSW = 1.85MHz
OUTPUT1 EFFICIENCY
vs. LOAD CURRENT
MAX5098A toc03
LOAD (A)
OUTPUT1 EFFICIENCY (%)
1.81.61.2 1.40.6 0.8 1.00.4
10
20
30
40
50
60
70
80
90
100
0
0.2 2.0
VIN = 8V
VIN = 14V VIN = 16V
VOUT = 5V
fSW = 300kHz
L1 = 18μH
OUTPUT2 EFFICIENCY
vs. LOAD CURRENT
MAX5098A toc04
LOAD (A)
OUTPUT2 EFFICIENCY (%)
0.90.80.6 0.70.4 0.50.30.2 1.0
10
20
30
40
50
60
70
80
90
100
0
VIN = 16V
VIN = 8V
VIN = 14V
VIN = 5.5V
VIN = 4.5V
VOUT = 3.3V
fSW = 300kHz
L2 = 27μH
OUTPUT1 VOLTAGE
vs. LOAD CURRENT
MAX5098A toc05
LOAD (A)
OUTPUT1 VOLTAGE (V)
1.81.61.41.21.00.80.60.4
4.92
4.94
4.96
4.98
5.00
4.90
0.2 2.0
VIN = 8V VIN = 14V VIN = 16V
VOUT = 5V
fSW = 1.85MHz
OUTPUT2 VOLTAGE
vs. LOAD CURRENT
MAX5098A toc06
LOAD (A)
OUTPUT2 VOLTAGE (V)
0.90.80.70.60.50.40.3
3.22
3.24
3.26
3.28
3.30
3.20
0.2 1.0
VIN = 5.5V VIN = 16V
VIN = 14V
VOUT = 3.3V
fSW = 1.85MHz
VL OUTPUT VOLTAGE
vs. CONVERTER SWITCHING FREQUENCY
MAX5098A toc07
CONVERTER SWITCHING FREQUENCY (kHz)
VL OUTPUT VOLTAGE (V)
17001200700
4.2
4.4
4.6
4.8
5.0
5.2
5.4
4.0
200 2200
VIN = 4.5V
VIN = 5.5V VIN = 8V VIN = 19V
VIN = 5V
BOTH CONVERTERS SWITCHING
FSEL_1 = VL
EACH CONVERTER SWITCHING
FREQUENCY vs. ROSC
MAX5098A toc08
ROSC (kΩ)
SWITCHING FREQUENCY (MHz)
604020
1
080
10
0.1
CONVERTER 1, CONVERTER 2
CONVERTER 1
FSEL_1 = VL,
FSEL_1 = GND,
EACH CONVERTER SWITCHING
FREQUENCY vs. TEMPERATURE
MAX5098A toc09
TEMPERATURE (°C)
SWITCHING FREQUENCY (MHz)
-5 30 65 100
1
10
0.1
-40 135
0.3MHz
0.6MHz
1.25MHz
1.85MHz 2.2MHz
FSEL_1 = VL
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
_______________________________________________________________________________________
7
LINE-TRANSIENT RESPONSE
(BUCK CONVERTER)
MAX5098A toc10
1ms/div
VIN
5V/div
VOUT1 = 5.0V/1.5A
AC-COUPLED
200mV/div
VOUT2 = 3.3V/0.75A
AC-COUPLED
200mV/div
0V
CONVERTER 1
LOAD-TRANSIENT RESPONSE
MAX5098A toc11
100μs/div
VOUT1 = 5.0V
AC-COUPLED
200mV/div
IOUT1
1A/div
0A
CONVERTER 2
LOAD-TRANSIENT RESPONSE
MAX5098A toc12
100μs/div
VOUT2 = 3.3V
AC-COUPLED
200mV/div
IOUT2
500mA/div
0A
SOFT-START/SOFT-STOP FROM EN1
MAX5098A toc13
1ms/div
VOUT1 = 5V/2A
5V/div
EN1
5V/div
PGOOD1
5V/div
0V
0V
0V
fSW = 1.85MHz
SOFT-START FROM ON/OFF
MAX5098A toc14
2ms/div
VOUT1 = 5V/2A
5V/div
ON/OFF
5V/div
GATE
10V/div
V+
10V/div
VL = EN1 = EN2
5V/div
0V
0V
0V
0V
OUT-OF-PHASE OPERATION
(FSEL_1 = VL)
MAX5098A toc15
200ns/div
SOURCE2
10V/div
SOURCE1
10V/div
CKO
5V/div
0V
0V
0V
Typical Operating Characteristics (continued)
(See the
Typical Application Circuit
, unless otherwise noted. V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means
that N1 is shorted externally.)
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
8 _______________________________________________________________________________________
OUT-OF-PHASE OPERATION
(FSEL_1 = SGND)
MAX5098A toc16
200ns/div
SOURCE2
10V/div
SOURCE1
10V/div
CKO
5V/div
0V
0V
0V
EXTERNAL SYNCHRONIZATION
(FSEL_1 = VL)
MAX5098A toc17
200ns/div
SOURCE2
10V/div
SOURCE1
10V/div
CKO
5V/div
0V
0V
SYNC
5V/div
0V
0V
EXTERNAL SYNCHRONIZATION
(FSEL_1 = SGND )
MAX5098A toc18
200ns/div
SOURCE2
10V/div
SOURCE1
10V/div
CKO
5V/div
0V
0V
SYNC
5V/div
0V
0V
FOUR-PHASE OPERATION
(FSEL_1 = VL )
MAX5098A toc19
200ns/div
MASTER SOURCE1
20V/div
MASTER SOURCE2
20V/div
SLAVE SOURCE1
20V/div
SLAVE SOURCE2
20V/div
MASTER
CKO
5V/div
0V
0V
0V
0V
0V
OVP BEHAVIOR
MAX5098A toc20
1ms/div
V+
10V/div
GATE
10V/div
VOUT1
10V/div
PGOOD2
10V/div
VOUT2
10V/div
EXTERNAL OVERVOLTAGE REMOVED
0V
0V
0V
0V
0V
FB_ VOLTAGE
vs. TEMPERATURE
MAX5098A toc21
TEMPERATURE (°C)
FB_ VOLTAGE (V)
10065-5 30
0.790
0.795
0.800
0.805
0.815
0.810
0.820
0.825
0.785
-40 135
VL = V+ = VIN_HIGH = 5.5V
Typical Operating Characteristics (continued)
(See the
Typical Application Circuit
, unless otherwise noted. V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means
that N1 is shorted externally.)
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
_______________________________________________________________________________________
9
BYPASS VOLTAGE
vs. TEMPERATURE
MAX5098A toc22
TEMPERATURE (°C)
BYPASS VOLTAGE (V)
10065-5 30
1.994
1.996
1.998
2.000
2.002
2.006
2.004
2.008
2.010
1.990
1.992
-40 135
VL = V+ = VIN_HIGH = 5.5V
BYPASS VOLTAGE
vs. BYPASS CURRENT
MAX5098A toc23
BYPASS CURRENT (μA)
BYPASS VOLTAGE (V)
806020 40
1.992
1.994
1.998
1.996
2.000
1.990
0 100705010 30 90
TA = +25°C
TA = +135°C
TA = +125°C
TA = +85°C
TA = -40°C
SOURCE1, SOURCE1 INDICATOR CURRENT,
SOURCE2, SOURCE2 INDICATOR CURRENT
MAX5098A toc24
1μs/div
ISOURCE1
500mA/div
NO LOAD
SOURCE1
20V/div
NO LOAD
SOURCE2
20V/div
ISOURCE2
1A/div
0V
0A
0A
0V
Typical Operating Characteristics (continued)
(See the
Typical Application Circuit
, unless otherwise noted. V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means
that N1 is shorted externally.)
V+ SWITCHING SUPPLY CURRENT
vs. SWITCHING FREQUENCY
MAX5098A toc25
SWITCHING FREQUENCY (kHz)
V+ SWITCHING SUPPLY CURRENT (mA)
182014401060680
10
20
30
40
50
0
300 2200
TA = +25°C
TA = +135°C
TA = +125°C
TA = +85°C
TA = -40°C
V+ = IN_HIGH = ON/OFF
V+ STANDBY SUPPLY CURRENT
vs. TEMPERATURE
MAX5098A toc26
TEMPERATURE (°C)
V+ STANDBY SUPPLY CURRENT (mA)
100500
1
2
3
4
0
-50 150
fSW = 1.85MHz
fSW = 300kHz
V+ = IN_HIGH = ON/OFF
EN1 = EN2 = SGND
IN_HIGH SHUTDOWN CURRENT
vs. TEMPERATURE
MAX5098A toc27
TEMPERATURE (°C)
IN_HIGH SHUTDOWN CURRENT (μA)
100500
4
8
12
16
20
0
-50 150
IN_HIGH = 8V
IN_HIGH = 14V
IN_HIGH = 16V
ON/OFF = SGND
IN_HIGH STANDBY CURRENT
vs. TEMPERATURE
MAX5098A toc28
TEMPERATURE (°C)
IN_HIGH STANDBY CURRENT (μA)
100500
85
95
105
115
125
135
145
75
-50 150
IN_HIGH = 8V
IN_HIGH = 14V
IN_HIGH = 16V
ON/OFF = IN_HIGH
EN1 = EN2 = SGND
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
10 ______________________________________________________________________________________
Typical Operating Characteristics (continued)
(See the
Typical Application Circuit
, unless otherwise noted. V+ = VIN_HIGH = 14V, unless otherwise noted. V+ = VIN_HIGH means
that N1 is shorted externally.)
IN_HIGH CLAMP VOLTAGE
vs. CLAMP CURRENT
MAX5098A toc29
CLAMP CURRENT (mA)
IN_HIGH CLAMP VOLTAGE (V)
40302010
20.0
20.1
20.2
20.3
19.9
050
TA = +25°C
TA = +135°C
TA = +125°C
TA = +85°C
TA = -40°C
V+ TO IN_HIGH CLAMP VOLTAGE
vs. GATE SINK CURRENT
MAX5098A toc30
GATE SINK CURRENT (mA)
V+ TO IN_HIGH CLAMP VOLTAGE (V)
8642
1
2
3
4
5
0
010
TA = +25°C
TA = +135°C
TA = +125°C
TA = +85°C
TA = -40°C
(VGATE - V) vs. VIN_HIGH
MAX5098A toc31
VIN_HIGH (V)
(VGATE - V) (V)
15.512.08.5
2
4
6
8
10
0
5.0 19.0
TA = +25°C
TA = +135°C
TA = +125°C
TA = +85°C
TA = -40°C
ON/OFF = IN_HIGH
SYSTEM TURN-ON FROM BATTERY
MAX5098A toc32
10ms/div
VL
10V/div
V+
10V/div
GATE
10V/div
IN_HIGH
10V/div
VIN
10V/div
0V
0V
0V
0V
0V
SYSTEM TURN-OFF FROM BATTERY
MAX5098A toc33
10ms/div
VL
10V/div
V+
10V/div
GATE
10V/div
IN_HIGH
10V/div
VIN
10V/div
0V
0V
0V
0V
0V
SYSTEM LOAD-DUMP
MAX5098A toc34
100ms/div
VOUT1
AC-COUPLED
100mV/div
V+
10V/div
GATE
10V/div
IN_HIGH
10V/div
0V
0V
0V
0V
0V
VIN
50V/div
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 11
Pin Description
PIN NAME FUNCTION
1, 32 SOURCE2 Converter 2 Internal MOSFET Source Connection. For buck converter operation, connect SOURCE2 to the
switched side of the inductor. For boost operation, connect SOURCE2 to PGND_ (Figure 6).
2, 3 DRAIN2
Converter 2 Internal MOSFET Drain Connection. For buck converter operation, use the MOSFET as a high-
side switch and connect DRAIN2 to the DC-DC converters supply input rail. For boost converter operation,
use the MOSFET as a low-side switch and connect DRAIN2 to the inductor and diode junction (Figure 6).
4 PGOOD2
Converter 2 Open-Drain Power-Good Output. PGOOD2 goes low when converter 2’s output falls below
92.5% of its set regulation voltage. Use PGOOD2 and EN1 to sequence the converters. Converter 2 starts
first.
5 EN2 Converter 2 Active-High Enable Input. Connect to VL for always-on operation.
6 FB2
Converter 2 Feedback Input. Connect FB2 to a resistive divider between converter 2’s output and SGND to
adjust the output voltage. To set the output voltage below 0.8V, connect FB2 to a resistive voltage-divider
from BYPASS to regulator 2’s output (Figure 3). See the Setting the Output Voltage section.
7 COMP2 Converter 2 Internal Transconductance Amplifier Output. See the Compensation section.
8 OSC
Oscillator Frequency Set Input. Connect a resistor from OSC to SGND (ROSC) to set the switching frequency
(see the Setting the Switching Frequency section). Set ROSC for an oscillator frequency equal to the SYNC
input frequency when using external synchronization. ROSC is still required when an external clock is
connected to the SYNC input. See the Synchronization (SYNC)/Clock Output (CKO) section.
9 SYNC
External Clock Synchronization Input. Connect SYNC to a 400kHz to 4400kHz clock to synchronize the
switching frequency with the system clock. Each converter frequency is 1/2 of the frequency applied to
SYNC (FSEL_1 = VL). For FSEL_1 = SGND, the switching frequency of converter 1 becomes 1/4 of the
SYNC frequency. Connect SYNC to SGND when not used.
10 GATE
Gate Drive Output. Connect to the gate of the external n-channel load-dump protection MOSFET. GATE =
IN_HIGH + 9V (typ) with IN_HIGH = 12V. GATE pulls to IN_HIGH by an internal n-channel MOSFET when V+
raises 2V above IN_HIGH. Leave gate unconnected if the load-dump protection is not used (MOSFET not
installed).
11 ON/OFF
n-Channel Switch Enable Input. Drive ON/OFF high for normal operation. Drive ON/OFF low to turn off the
external n-channel load-dump protection MOSFET and reduce the supply current to 7µA (typ). When
ON/OFF is driven low, both DC-DC converters are disabled and the PGOOD_ outputs are driven low.
Connect to V+ if the external load-dump protection is not used (MOSFET not installed).
12 IN_HIGH
Startup Input. IN_HIGH is protected by internally clamping to 21V (max). Connect a resistor (4kΩ max) from
IN_HIGH to the drain of the protection switch. Bypass IN_HIGH with a 4.7µF electrolytic or 1µF minimum
ceramic capacitor. Connect to V+ if the external load-dump protection is not used (MOSFET not installed).
13 V+ Input Supply Voltage. V+ can range from 5.2V to 19V. Connect V+, IN_HIGH, and VL together for 4.5V to
5.5V input operation. Bypass V+ to SGND with a 1µF minimum ceramic capacitor.
14 VL
Internal Regulator Output. The VL regulator is used to supply the drive current at input VDRV. When driving
VDRV, use an RC lowpass filter to decouple switching noise from VDRV to the VL regulator (see the Typical
Application Circuit). Bypass VL to SGND with a 4.7µF minimum ceramic capacitor.
15 SGND Signal Ground. Connect SGND to exposed pad and to the board signal ground plane. Connect the board
signal ground and power ground planes together at a single point.
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
12 ______________________________________________________________________________________
Pin Description (continued)
PIN NAME FUNCTION
16 BYPASS Reference Output Bypass Connection. Bypass to SGND with a 0.22µF or greater ceramic capacitor.
17 FSEL_1
Converter 1 Frequency Select Input. Connect FSEL_1 to VL for normal operation. Connect FSEL_1 to SGND
to reduce converter 1’s switching frequency to 1/2 of converter 2’s switching frequency (converter 1
switching frequency is 1/4 the CKO frequency). Do not leave FSEL_1 unconnected.
18 COMP1 Converter 1 Internal Transconductance Amplifier Output. See the Compensation section.
19 FB1
Converter 1 Feedback Input. Connect FB1 to a resistive divider between converter 1’s output and SGND to
adjust the output voltage. To set the output voltage below 0.8V, connect FB1 to a resistive voltage-divider
from BYPASS to regulator 1’s output (Figure 3). See the Setting the Output Voltage section.
20 EN1 Converter 1 Active-High Enable Input. Connect to VL for an always-on operation.
21 PGOOD1
Converter 1 Open-Drain Power-Good Output. PGOOD1 output goes low when converter 1’s output falls
below 92.5% of its set regulation voltage. Use PGOOD1 and EN2 to sequence the converters. Converter 1
starts first.
22, 23 DRAIN1
Converter 1 Internal MOSFET Drain Connection. For buck converter operation, use the MOSFET as a high-
side switch and connect DRAIN1 to the DC-DC converters supply input rail. For boost converter operation,
use the MOSFET as a low-side switch and connect DRAIN1 to the inductor and diode junction (Figure 6).
24, 25 SOURCE1 Converter 1 Internal MOSFET Source Connection. For buck operation, connect SOURCE1 to the switched
side of the inductor. For boost operation, connect SOURCE1 to PGND_ (Figure 6).
26 BST1/VDD1
Converter 1 Bootstrap Flying-Capacitor Connection. For buck converter operation, connect BST1/VDD1 to a
0.1µF ceramic capacitor and diode according to the Typical Application Circuit. For boost converter
operation, driver bypass capacitor connection. Connect to VDRV and bypass with a 0.1µF ceramic
capacitor to PGND_ (Figure 6).
27 VDRV
Low-Side Driver Supply Input. Connect VDRV to VL through an RC filter to bypass switching noise to the
internal VL regulator. For buck converter operation, connect anode terminals of external bootstrap diodes to
VDRV. For boost converter operation, connect VDRV to BST1/VDD1 and BST2/VDD2. Bypass with a
minimum 2.2µF ceramic capacitor to PGND_ (see the Typical Application Circuit). Do not connect to an
external supply.
28 CKO
Clock Output. CKO is an output with twice the frequency of each converter (FSEL_1 = VL) and 90° out-of-
phase with respect to converter 1. Connect CKO to the SYNC input of another MAX5098A for a four-phase
converter.
29, 30 PGND1,
PGND2 Power Ground. Connect both PGND1 and PGND2 together and to the board power ground plane.
31 BST2/VDD2
Converter 2 Bootstrap Flying-Capacitor Connection. For buck converter operation, connect BST2/VDD2 to a
0.1µF ceramic capacitor and diode according to the Typical Application Circuit. For boost converter
operation, driver bypass capacitor connection. Connect to VDRV and bypass with a 0.1µF ceramic
capacitor from BST2/VDD2 to PGND_ (Figure 6).
—EP
Exposed Pad. Connect EP to SGND. For enhanced thermal dissipation, connect EP to a copper area as
large as possible. Do not use EP as the sole ground connection.
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 13
Functional Diagram
CONVERTER 1
COMP1
PGOOD1
SOURCE1
DRAIN1
V+
BYPASS
FSEL_1
EN1
SYNC
OSC
VDRV
CKO
EN2
DRAIN2
PGOOD2
CONVERTER 2
VL
CKO2
LDO
Q
S
R
0.2V 0.74V
0.8V
TRANSCONDUCTANCE
ERROR AMPLIFIER
fSW/4
FREQUENCY
CONTROL
PWM
COMPARATOR
CKO1
MAXIMUM DUTY-CYCLE
CONTROL
FB1
VL
VL
BST1/VDD1
IN_HIGH
ON/OFF
0.9V
PGND_
CURRENT
LIMIT
OSCILLATOR
MAIN
OSCILLATOR
GATE
OVERVOLTAGE
OVERVOLTAGE
STARTUP CIRCUIT/
PROTECTION CIRCUIT/
CHARGE PUMP
20V SHUNT
REGULATOR
1.8V
SGND
Q
BST2/VDD2
SOURCE2
FB2
PGND_
COMP2
CHARGE
PUMP
DIGITAL
SOFT-START
FREQUENCY
DIVIDER
MAX5098A
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
14 ______________________________________________________________________________________
Detailed Description
PWM Controller
The MAX5098A dual DC-DC converter uses a pulse-
width-modulation (PWM) voltage-mode control scheme.
On each converter the device includes one integrated
n-channel MOSFET switch and requires an external
low-forward-drop Schottky diode for output rectifica-
tion. The controller generates the clock signal by divid-
ing down the internal oscillator (fCKO) or the SYNC
input when driven by an external clock, therefore each
controller’s switching frequency equals half the oscilla-
tor frequency (fSW = fCKO/2) or half of the SYNC input
frequency (fSW = fSYNC/2). An internal transconduc-
tance error amplifier produces an integrated error volt-
age at COMP_, providing high DC accuracy. The
voltage at COMP_ sets the duty cycle using a PWM
comparator and a ramp generator. At each rising edge
of the clock, converter 1’s MOSFET switch turns on and
remains on until either the appropriate or maximum
duty cycle is reached, or the maximum current limit for
the switch is reached. Converter 2 operates 180° out-
of-phase, so its MOSFET switch turns on at each falling
edge of the clock.
In the case of buck operation (see the
Typical
Application Circuit
), the internal MOSFET is used in
high-side configuration. During each MOSFET’s on-
time, the associated inductor current ramps up. During
the second half of the switching cycle, the high-side
MOSFET turns off and forward biases the Schottky rec-
tifier. During this time, the SOURCE_ voltage is
clamped to a diode drop (VD) below ground. A low for-
ward voltage drop (0.4V) Schottky diode must be used
to ensure the SOURCE_ voltage does not go below
-0.6V abs max. The inductor releases the stored energy
as its current ramps down, and provides current to the
output. The bootstrap capacitor is also recharged when
the SOURCE_ voltage goes low during the high-side
MOSFET off-time. The maximum duty-cycle limit
ensures proper bootstrap charging at startup or low
input voltages. The circuit goes in discontinuous con-
duction mode operation at light load, when the inductor
current completely discharges before the next cycle
commences. Under overload conditions, when the
inductor current exceeds the peak current limit of the
respective switch, the high-side MOSFET turns off
quickly and waits until the next clock cycle.
In the case of boost operation, the MOSFET is a low-
side switch (Figure 6). During each on-time, the induc-
tor current ramps up. During the second half of the
switching cycle, the low-side switch turns off and for-
ward biases the Schottky diode. During this time, the
DRAIN_ voltage is clamped to a diode drop (VD) above
VOUT_ and the inductor provides energy to the output
as well as replenishes the output capacitor charge.
Load-Dump Protection
Most automotive applications are powered by a multi-
cell, 12V lead-acid battery with a voltage from 9V to
16V (depending on load current, charging status, tem-
perature, battery age, etc.). The battery voltage is dis-
tributed throughout the automobile and is locally
regulated down to voltages required by the different
system modules. Load dump occurs when the alterna-
tor is charging the battery and the battery becomes
disconnected. Power in the alternator inductance flows
into the distributed power system and elevates the volt-
age seen at each module. The voltage spikes have rise
times typically greater than 5ms and decays within sev-
eral hundred milliseconds but can extend out to 1s or
more depending on the characteristics of the charging
system. These transients are capable of destroying
sensitive electronic equipment on the first fault event.
During load dump, the MAX5098A provides the ability
to clamp the input-voltage rail of the internal DC-DC
converters to a safe level, while preventing power dis-
continuity at the DC-DC converters’ outputs.
The load-dump protection circuit utilizes an internal
charge pump to drive the gate of an external n-channel
MOSFET. This series protection MOSFET absorbs the
load-dump overvoltage transient and operates in satu-
ration over the normal battery range to minimize power
dissipation. During load dump, the gate voltage of the
protection MOSFET is regulated to prevent the source
terminal from exceeding 19V.
The DC-DC converters are powered from the source
terminal of the load-dump protection MOSFET, so that
their input voltage is limited during load-dump and can
operate normally.
ON/OFF
The MAX5098A provides an input (ON/OFF) to turn on
and off the external load-dump protection MOSFET.
Drive ON/OFF high for normal operation. Drive ON/OFF
low to turn off the external n-channel load-dump protec-
tion MOSFET and reduce the supply current to 7µA (typ).
When ON/OFF is driven low, the converter also turns off,
and the PGOOD_ outputs are driven low. V+ will be self
discharged through the converters output currents and
the IC supply current.
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 15
Internal Oscillator/Out-of-Phase Operation
The internal oscillator generates the 180° out-of-phase
clock signal required by each regulator. The switching
frequency of each converter (fSW) is programmable
from 200kHz to 2.2MHz using a single 1% resistor at
ROSC. See the
Setting the Switching Frequency
section.
With dual synchronized out-of-phase operation, the
MAX5098A’s internal MOSFETs turn on 180° out-of-
phase. The instantaneous input current peaks of both
regulators do not overlap, resulting in reduced RMS rip-
ple current and input-voltage ripple. This reduces the
required input capacitor ripple current rating, allows for
fewer or less expensive capacitors, and reduces
shielding requirements for EMI.
Synchronization (SYNC)/
Clock Output (CKO)
The main oscillator can be synchronized to the system
clock by applying an external clock (fSYNC) at SYNC.
The fSYNC frequency must be twice the required oper-
ating frequency of an individual converter. Use a TTL
logic signal for the external clock with at least 100ns
pulse width. ROSC is still required when using external
synchronization. Program the internal oscillator fre-
quency to have fSW = 1/2 fSYNC. The device is properly
synchronized if the SYNC frequency, fSYNC, varies
within ±20%.
Two MAX5098As can be connected in the master-slave
configuration for four ripple-phase operation (Figure 1).
The MAX5098A provides a clock output (CKO) that is
45° phase-shifted with respect to the internal switch
turn-on edge. Feed the CKO of the master to the SYNC
input of the slave. The effective input ripple switching
frequency is four times the individual converter’s switch-
ing frequency. When driving the master converter using
an external clock at SYNC, set the fSYNC clock duty
cycle to 50% for effective 90° phase-shifted interleaved
operation. When a SYNC is applied (and FSEL_1 = 0),
converter 1 duty cycle is limited to 75% (max).
Input Voltage (V+)/
Internal Linear Regulator (VL)
All internal control circuitry operates from an internally
regulated nominal voltage of 5.2V (VL). At higher input
voltages (V+) of 5.2V to 19V, VLis regulated to 5.2V. At
5.2V or below, the internal linear regulator operates in
dropout mode, where VLfollows V+. Depending on the
load on VL, the dropout voltage can be high enough to
reduce VLbelow the undervoltage lockout (UVLO)
threshold. Do not use VLto power external circuitry.
For input voltages less than 5.5V, connect V+ and VL
together. The load on VLis proportional to the switching
frequency of converter 1 and converter 2. See the VL
Output Voltage vs. Converter Switching Frequency
graph in the
Typical Operating Characteristics
. For
input voltage ranges higher than 5.5V, disconnect VL
from V+.
Bypass V+ to SGND with a 1µF or greater ceramic
capacitor placed close to the MAX5098A. Bypass VL
with a 4.7µF ceramic capacitor to SGND.
Undervoltage Lockout/
Soft-Start/Soft-Stop
The MAX5098A includes an undervoltage lockout with
hysteresis and a power-on-reset circuit for converter
turn-on and monotonic rise of the output voltage. The
falling UVLO threshold is internally set to 4.1V (typ) with
180mV hysteresis. Hysteresis at UVLO eliminates “chat-
tering” during startup. When VLdrops below UVLO, the
internal MOSFET switches are turned off.
The MAX5098A digital soft-start reduces input inrush
currents and glitches at the input during turn-on. When
UVLO is cleared and EN_ is high, digital soft-start slow-
ly ramps up the internal reference voltage in 64 steps.
The total soft-start period is 4096 internal oscillator
switching cycles.
Driving EN_ low initiates digital soft-stop that slowly
ramps down the internal reference voltage in 64 steps.
The total soft-stop period is equal to the soft-start period.
To calculate the soft-start/soft-stop period, use the fol-
lowing equation:
where fCKO is the internal oscillator and fCKO is twice
each converters’ switching frequency (FSEL_1 = VL)
Enable (EN1, EN2)
The MAX5098A dual converter provides separate
enable inputs, EN1 and EN2, to individually control or
sequence the output voltages. These active-high enable
inputs are TTL compatible. Driving EN_ high initiates
soft-start of the converter, and PGOOD_ goes logic-high
when the converter output voltage reaches the
VTPGOOD_ threshold. Driving EN_ low initiates a soft-
stop of the converter, and immediately forces PGOOD_
low. Use EN1, EN2, and PGOOD1 for sequencing (see
Figure 2). Connect PGOOD1 to EN2 to make sure con-
verter 1’s output is within regulation before converter 2
starts. Add an RC network from VLto EN1 and EN2 to
delay the individual converter. Sequencing reduces
input inrush current and possible chattering. Connect
EN_ to VLfor always-on operation.
tmsf kHz
SS CKO
() ()
=4096
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
16 ______________________________________________________________________________________
SYNCSYNC
SLAVEMASTER
V+
OUTPUT4 OUTPUT3
DRAIN2
SOURCE2
DRAIN1
SOURCE1
CKO
CLKIN
V+
OUTPUT2 OUTPUT1
CIN
VIN
DRAIN2
SOURCE2
DRAIN1
SOURCE1
SYNC
SOURCE1
(MASTER)
CKO
(MASTER)
SOURCE2
(MASTER)
SOURCE1
(SLAVE)
SOURCE2
(SLAVE)
CKO
(SLAVE)
CIN (RIPPLE)
SYNCPHASE
CKOPHASE
DUTY CYCLE = 50%
Figure 1. Synchronized Controllers
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 17
PGOOD_
Converter 1 and converter 2 include a power-good flag,
PGOOD1 and PGOOD2, respectively. Since PGOOD_
is an open-drain output and can sink 3mA while provid-
ing the TTL logic-low signal, pull PGOOD_ to a logic
voltage to provide a logic-level output. PGOOD1 goes
low when converter 1’s feedback FB1 drops to 92.5%
(VTPGOOD_) of its nominal set point. The same is true for
converter 2. Connect PGOOD_ to SGND or leave
unconnected if not used.
Current Limit
The internal MOSFET switch current of each converter is
monitored during its on-time. When the peak switch cur-
rent crosses the current-limit threshold of 3.45A (typ) and
2.1A (typ) for converter 1 and converter 2, respectively,
the on-cycle is terminated immediately and the inductor
is allowed to discharge. The MOSFET is turned on at the
next clock pulse, initiating a new switching cycle.
In deep overload or short-circuit conditions when the
VFB_ voltage drops below 0.2V, the switching frequen-
cy is reduced to 1/4 x fSW to provide sufficient time for
the inductor to discharge. During overload conditions, if
the voltage across the inductor is not high enough to
allow for the inductor current to properly discharge,
current runaway may occur. Current runaway can
destroy the device in spite of internal thermal-overload
protection. Reducing the switching frequency during
overload conditions allows more time for inductor dis-
charge and prevents current runaway.
Output Overvoltage Protection
The MAX5098A outputs are protected from output volt-
age overshoots due to input transients and shorting the
output to a high voltage. When the output voltage rises
above the overvoltage threshold, 110% (typ) nominal
FB_, the overvoltage condition is triggered. When the
overvoltage condition is triggered on either channel,
both converters are immediately turned off, 20Ωpull-
down switches from SOURCE_ to PGND_ are turned on
to help the output-voltage discharge, and the gate of
the load-dump protection external MOSFET is pulled
low. The device restarts as soon as both converter out-
puts discharge, bringing both FB_ input voltages below
12.5V of their nominal set points.
Thermal-Overload Protection
During continuous short circuit or overload at the out-
put, the power dissipation in the IC can exceed its limit.
The MAX5098A provides thermal shutdown protection
with temperature hysteresis. Internal thermal shutdown
is provided to avoid irreversible damage to the device.
When the die temperature exceeds +165°C (typ), an
on-chip thermal sensor shuts down the device, forcing
the internal switches to turn off, allowing the IC to cool.
The thermal sensor turns the part on again with soft-
start after the junction temperature cools by +20°C.
During thermal shutdown, both regulators shut down,
PGOOD_ goes low, and soft-start resets. The internal
20V zener clamp from IN_HIGH to SGND is not turned
off during thermal shutdown because clamping action
must be always active.
FB1FB2
EN1EN2 VL
R1R2
C1C2
VL
VLV+
MAX5098A
OUTPUT2 OUTPUT1
DRAIN2
SOURCE2
DRAIN1
SOURCE1
VIN
VL
FB1FB2
EN1EN2
SEQUENCING—OUTPUT 2 DELAYED WITH RESPECT TO OUTPUT 1. R1/C1 AND R2/C2 ARE SIZED FOR REQUIRED SEQUENCING.
VL
VL
VLV+
MAX5098A
OUTPUT2 OUTPUT1
DRAIN2
SOURCE2
DRAIN1
SOURCE1
PGOOD1
VIN
VL
Figure 2. Power-Supply Sequencing Configurations
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
18 ______________________________________________________________________________________
Applications Information
Setting the Switching Frequency
The controller generates the clock signal by dividing
down the internal oscillator fOSC or the SYNC input sig-
nal when driven by an external oscillator. The switching
frequency equals half the internal oscillator frequency
(fSW = fOSC/2). The internal oscillator frequency is set
by a resistor (ROSC) connected from OSC to SGND. To
find ROSC for each converter switching frequency fSW,
use the formulas:
A rising clock edge on SYNC is interpreted as a syn-
chronization input. If the SYNC signal is lost, the inter-
nal oscillator takes control of the switching rate,
returning the switching frequency to that set by ROSC.
When an external synchronization signal is used, ROSC
must be selected such that fSW = 1/2 fSYNC. When
fSYNC clock signal is applied, fCKO equals fSYNC wave-
form, phase shifted by 180°. If the MAX5098A is run-
ning without external synchronization, fCKO equals the
internal oscillator frequency fOSC.
Buck Converter
Effective Input Voltage Range
Although the MAX5098A converter can operate from
input supplies ranging from 5.2V to 19V, the input volt-
age range can be effectively limited by the MAX5098A
duty-cycle limitations for a given output voltage. The
maximum input voltage is limited by the minimum on-
time (tON(MIN)):
where tON(MIN) is 100ns. The minimum input voltage is
limited by the maximum duty cycle (DMAX = 0.82):
where VDROP1 is the total parasitic voltage drops in the
inductor discharge path, which includes the forward
voltage drop (VD) of the rectifier, the series resistance
of the inductor, and the PCB resistance. VDROP2 is the
total resistance in the charging path that includes the
on-resistance of the high-side switch, the series resis-
tance of the inductor, and the PCB resistance.
Setting the Output Voltage
For 0.8V or greater output voltages, connect a voltage-
divider from OUT_ to FB_ to SGND (Figure 3). Select RB
(FB_ to SGND resistor) to between 1kΩand 20kΩ.
Calculate RA(OUT_ to FB_ resistor) with the following
equation:
where VFB_ = 0.8V (see the
Electrical Characteristics
table) and VOUT_ can range from VFB_ to 28V (boost
operation).
For output voltages below 0.8V, set the MAX5098A out-
put voltage by connecting a voltage-divider from OUT_
to FB_ to BYPASS (Figure 3). Select RC(FB_ to BYPASS
resistor) in the 50kΩrange. Calculate RAwith the fol-
lowing equation:
where VFB_ = 0.8V, VBYPASS = 2V (see the
Electrical
Characteristics
table), and VOUT_ can range from 0V to
VFB_.
RRVV
VV
AC
FB OUT
BYPASS FB
=⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
−
−
__
_
RRV
V
AB
OUT
FB
=⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
−
_
_
1
VVV
DVV
IN MIN OUT DROP
MAX DROP DROP()
=+
⎡
⎣
⎢⎤
⎦
⎥+−
121
VV
tf
IN MAX OUT
ON MIN SW
() ()
≤×
Rk
f MHz
f MHz
Rk
f MHz
f MHz
OSC
SW
SW
OSC
SW
SW
Ω
Ω
()
=
()
≥
()
()
=
()
<
()
10 721 125
12 184 125
0 920
0 973
..
..
.
.
RA
VOUT_
VOUT_
SOURCE_
FB_
VOUT_ ≥ 0.8V
RB
MAX5098A
RC
FB_
SOURCE_
BYPASS
VOUT_ < 0.8V
RA
MAX5098A
Figure 3. Adjustable Output Voltage
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 19
Inductor Selection
Three key inductor parameters must be specified for
operation with the MAX5098A: inductance value (L),
peak inductor current (IL), and inductor saturation cur-
rent (ISAT). The minimum required inductance is a func-
tion of operating frequency, input-to-output voltage
differential and the peak-to-peak inductor current (ΔIL).
A good compromise is to choose ΔILequal to 30% of
the full load current. To calculate the inductance, use
the following equation:
where VIN and VOUT are typical values (so that efficien-
cy is optimum for typical conditions). The switching fre-
quency is set by ROSC (see the
Setting the Switching
Frequency
section). The peak-to-peak inductor current,
which reflects the peak-to-peak output ripple, is worse
at the maximum input voltage. See the
Output
Capacitor
section to verify that the worst-case output
ripple is acceptable. The inductor saturation current is
also important to avoid runaway current during output
overload and continuous short circuit. Select the ISAT to
be higher than the maximum peak current limits of 4.3A
and 2.6A for converter 1 and converter 2.
Input Capacitor
The discontinuous input current waveform of the buck
converter causes large ripple currents at the input. The
switching frequency, peak inductor current, and the
allowable peak-to-peak voltage ripple dictate the input
capacitance requirement. Note that the two converters
of the MAX5098A run 180° out-of-phase, thereby effec-
tively doubling the switching frequency at the input.
The input ripple waveform would be unsymmetrical due
to the difference in load current and duty cycle
between converter 1 and converter 2. The worst-case
mismatch is when one converter is at full load while the
other converter is at no load or in shutdown. The input
ripple is comprised of ΔVQ(caused by the capacitor
discharge) and ΔVESR (caused by the ESR of the
capacitor). Use ceramic capacitors with high ripple-
current capability at the input, connected between
DRAIN_ and PGND_. Assume the contribution from the
ESR and capacitor discharge equal to 50%. Calculate
the input capacitance and ESR required for a specified
ripple using the following equations:
where
and
where
where IOUT is the maximum output current from either
converter 1 or converter 2, and D is the duty cycle for
that converter. The frequency of each individual con-
verter is fSW. For example, at VIN = 12V, VOUT = 3.3V at
IOUT = 2A, and with L = 3.3µH, the ESR and input
capacitance are calculated for a peak-to-peak input rip-
ple of 100mV or less, yielding an ESR and capacitance
value of 20mΩand 6.8µF for 1.25MHz frequency. At low
input voltages, also add one electrolytic bulk capacitor
of at least 100µF on the converters’ input voltage rail.
This capacitor acts as an energy reservoir to avoid pos-
sible undershoot below the undervoltage lockout thresh-
old during power-on and transient loading.
Output Capacitor
The allowable output ripple voltage and the maximum
deviation of the output voltage during step load cur-
rents determines the output capacitance and its ESR.
The output ripple is comprised of ΔVQ(caused by the
capacitor discharge) and ΔVESR (caused by the ESR of
the capacitor). Use low-ESR ceramic or aluminum elec-
trolytic capacitors at the output. For aluminum elec-
trolytic capacitors, the entire output ripple is
contributed by ΔVESR. Use the ESROUT equation to cal-
culate the ESR requirement and choose the capacitor
accordingly. If using ceramic capacitors, assume the
contribution to the output ripple voltage from the ESR
and the capacitor discharge are equal. Calculate the
output capacitance and ESR required for a specified
ripple using the following equations:
ESR V
I
CI
Vf
OUT ESR
L
OUT L
QSW
=
=××
Δ
Δ
Δ
Δ8
DV
V
OUT
IN
=
CIDD
Vf
IN OUT
QSW
=×
()
×
−1
Δ
ΔIVV V
Vf L
LIN OUT OUT
IN SW
=
()
×
××
−
ESR V
II
IN ESR
OUT L
=
+
Δ
Δ
2
LVVV
Vf I
OUT IN OUT
IN SW L
=
()
××
−
Δ
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
20 ______________________________________________________________________________________
where
ΔILis the peak-to-peak inductor current as calculated
above and fSW is the individual converter’s switching
frequency.
The allowable deviation of the output voltage during
fast transient loads also determines the output capaci-
tance and its ESR. The output capacitor supplies the
step load current until the controller responds with a
greater duty cycle. The response time (tRESPONSE)
depends on the closed-loop bandwidth of the convert-
er. The high switching frequency of the MAX5098A
allows for higher closed-loop bandwidth, reducing
tRESPONSE and the output capacitance requirement.
The resistive drop across the output capacitor ESR and
the capacitor discharge causes a voltage droop during
a step load. Use a combination of low-ESR tantalum or
polymer and ceramic capacitors for better transient
load and ripple/noise performance. Keep the maximum
output voltage deviation within the tolerable limits of the
electronics being powered. When using a ceramic
capacitor, assume 80% and 20% contribution from the
output capacitance discharge and the ESR drop,
respectively. Use the following equations to calculate
the required ESR and capacitance value:
where ISTEP is the load step and tRESPONSE is the
response time of the controller. Controller response
time depends on the control-loop bandwidth.
Boost Converter
The MAX5098A can be configured for step-up conver-
sion since the internal MOSFET can be used as a low-
side switch. Use the following equations to calculate
the values for the inductor (LMIN), input capacitor (CIN),
and output capacitor (COUT) when using the converter
in boost operation.
Inductor
Choose the minimum inductor value so the converter
remains in continuous mode operation at minimum out-
put current (IOMIN).
where
The VDis the forward voltage drop of the external
Schottky diode, D is the duty cycle, and VDS is the volt-
age drop across the internal MOSFET switch. Select
the inductor with low DC resistance and with a satura-
tion current (ISAT) rating higher than the peak switch
current limit of 4.3A (ICL1) and 2.6A (ICL2) of converter
1 and converter 2, respectively.
Input Capacitor
The input current for the boost converter is continuous
and the RMS ripple current at the input is low. Calculate
the capacitor value and ESR of the input capacitor
using the following equations.
where
where VDS is the voltage drop across the internal
MOSFET switch. ΔILis the peak-to-peak inductor ripple
current as calculated above. ΔVQis the portion of input
ripple due to the capacitor discharge and ΔVESR is the
contribution due to ESR of the capacitor.
Output Capacitor
For the boost converter, the output capacitor supplies
the load current when the main switch is ON. The
required output capacitance is high, especially at high-
er duty cycles. Also, the output capacitor ESR needs to
be low enough to minimize the voltage drop due to the
ESR while supporting the load current. Use the follow-
ing equation to calculate the output capacitor for a
specified output ripple tolerance.
where IPK is the peak inductor current as defined in the
Power Dissipation
section for the boost converter, IOis
the load current, ΔVQis the portion of the ripple due to
ESR V
I
CID
Vf
ESR
PK
OUT O MAX
QSW
=
=×
×
Δ
Δ
ΔIVV D
Lf
LIN DS
SW
=
()
×
×
−
CI
fV
ESR V
I
IN L
SW Q
ESR
L
=××
=
Δ
Δ
Δ
Δ
8
DVVV
VVV
OD IN
ODDS
=+
+
−
−
LVD
fVI
MIN IN
SW O OMIN
=×
×××
2
2
ESR V
I
CIt
V
OUT ESR
STEP
OUT STEP RESPONSE
Q
=
=×
Δ
Δ
ΔΔΔVVV
O RIPPLE ESR Q_≅+
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 21
the capacitor discharge, and ΔVESR is the contribution
due to the ESR of the capacitor. DMAX is the maximum
duty cycle at minimum input voltage.
Power Dissipation
The MAX5098A includes two internal power MOSFET
switches. The DC loss is a function of the RMS current in
the switch while the switching loss is a function of switch-
ing frequency and instantaneous switch voltage and cur-
rent. Use the following equations to calculate the RMS
current, DC loss, and switching loss of each converter.
The MAX5098A is available in a thermally enhanced
package and can dissipate up to 2.7W at +70°C ambient
temperature. The total power dissipation in the package
must be limited so that the operating junction tempera-
ture does not exceed its absolute maximum rating of
+150°C at maximum ambient temperature.
For the buck converter:
where
See the
Electrical Characteristics
table for the
RON(MAX) maximum value.
For the boost converter:
where VDS is the drop across the internal MOSFET and
η is the efficiency. See the
Electrical Characteristics
table for the RON(MAX) value.
where tRand tFare rise and fall times of the internal
MOSFET. tFcan be measured in the actual application.
The supply current in the MAX5098A is dependent on
the switching frequency. See the
Typical Operating
Characteristics
to find the supply current of the
MAX5098A at a given operating frequency. The power
dissipation (PS) in the device due to supply current
(ISUPPLY) is calculated using following equation.
PS = VINMAX x ISUPPLY
The total power dissipation PTin the device is:
PT = PDC1 + PDC2 + PSW1 + PSW2 + PS
where PDC1 and PDC2 are DC losses in converter 1 and
converter 2, respectively. PSW1 and PSW2 are switching
losses in converter 1 and converter 2, respectively.
Calculate the temperature rise of the die using the fol-
lowing equation:
TJ = TCx (PT x θJC)
where θJC is the junction-to-case thermal impedance of
the package equal to +1.7°C/W. Solder the exposed
pad of the package to a large copper area to minimize
the case-to-ambient thermal impedance. Measure the
temperature of the copper area near the device at a
worst-case condition of power dissipation and use
+1.7°C/W as θJC thermal impedance.
Compensation
The MAX5098A provides an internal transconductance
amplifier with its inverting input and its output available
for external frequency compensation. The flexibility of
external compensation for each converter offers wide
selection of output filtering components, especially the
output capacitor. For cost-sensitive applications, use
aluminum electrolytic capacitors; for component size-
sensitive applications, use low-ESR tantalum, polymer,
or ceramic capacitors at the output. The high switching
frequency of MAX5098A allows use of ceramic capaci-
tors at the output.
Choose all the passive power components that meet
the output ripple, component size, and component cost
requirements. Choose the small-signal components for
the error amplifier to achieve the desired closed-loop
PVI tt f
SW OIN R F SW
=×× +
()
×
4
IIIII
D
IVI
V
IVV D
Lf
II I
II I
PI R
RMS DC PK DC PK MAX
IN OO
IN
LIN DS
SW
DC IN L
PK IN L
DC RMS DS ON MAX
=++×
()
()
×
=×
×
=
()
×
×
=
=+
=×
−
−
22
2
3
2
2
η
Δ
Δ
Δ
()( )
III
II I
PVI tt f
DC O L
PK O L
SW IN O R F SW
=
=+
=×× +
()
×
−Δ
Δ
2
2
4
IIIII
D
PI R
RMS DC PK DC PK MAX
DC RMS DS ON MAX
=++×
()
⎛
⎝⎞
⎠×
=×
22
2
3
()
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
22 ______________________________________________________________________________________
bandwidth and phase margin. Use a simple pole-zero
pair (Type II) compensation if the output capacitor ESR
zero frequency is below the unity-gain crossover fre-
quency (fC). Type III compensation is necessary when
the ESR zero frequency is higher than fCor when com-
pensating for a continuous mode boost converter that
has a right-half-plane zero.
Use procedure 1 to calculate the compensation net-
work components when fZERO,ESR < fC.
Buck Converter Compensation
Procedure 1 (See Figure 4)
1) Calculate the fZERO,ESR and LC double-pole fre-
quencies:
2) Select the unity-gain crossover frequency:
If the fZERO,ESR is lower than fCand close to fLC, use a
Type II compensation network where RFCFprovides a
midband zero fMID,ZERO, and RFCCF provides a high-
frequency pole.
3) Calculate modulator gain GMat the crossover fre-
quency.
where VOSC is a peak-to-peak ramp amplitude equal to
1V.
The transconductance error amplifier gain is:
GE/A = gMx RF
The total loop gain at fCshould be equal to 1:
GM x GE/A = 1
or
4) Place a zero at or below the LC double pole:
5) Place a high-frequency pole at fP= 0.5 x fSW.
Procedure 2 (See Figure 5)
If the output capacitor used is a low-ESR ceramic type,
the ESR frequency is usually far away from the targeted
unity crossover frequency (fC). In this case, Type III
compensation is recommended. Type III compensation
provides two-pole zero pairs. The locations of the zero
and poles should be such that the phase margin peaks
around fC. It is also important to place the two zeros at
or below the double pole to avoid the conditional stabil-
ity issue.
1) Select a crossover frequency:
2) Calculate the LC double-pole frequency, fLC:
f
LC
LC
OUT OUT
=××
1
2π
ff
CSW
≤20
CC
fRC
CF F
SW F F
=×××
()
−205 1π.
CRf
FFLC
=××
1
2π
RV ESR f L V
V g ESR
FOSC C OUT OUT
IN M
=+××
()
×
×××
2
08
π
.
GV
V
ESR
ESR f L V
MIN
OSC C OUT OUT
=×
+××
()
×
2
08
π
.
ff
CSW
≤20
fESR C
f
LC
ZERO ESR OUT
LC
OUT OUT
,=××
=×
1
2
1
2
π
π
R1
FB_
RF
COMP_
VOUT
VREF
CCF
CF
R2
-
+
gM
Figure 4. Type II Compensation Network
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 23
3) Place a zero
where
and RF≥10kΩ.
4) Calculate CIfor a target unity crossover frequency, fC.
5) Place a pole
or 5 x fC, whichever
is lower,
6) Place a second zero, fZ2, at 0.2 x fCor at fLC,
whichever is lower.
7) Place a second pole at 1/2 the switching frequency.
Boost Converter Compensation
The boost converter compensation gets complicated
due to the presence of a right-half-plane zero
fZERO,RHP. The right-half-plane zero causes a drop in
phase while adding positive (+1) slope to the gain
curve. It is important to drop the gain significantly below
unity before the RHP frequency. Use the following pro-
cedure to calculate the compensation components:
1) Calculate the LC double-pole frequency, fLC, and
the right-half-plane-zero frequency.
where
DV
V
RV
I
IN
OUT
MIN OUT
OUT MAX
=
=
−
()
1
()
f
DR
L
ZERO RHP
MIN
OUT
,=
()
×
−
()
1
2
2
π
fD
LC
LC
OUT OUT
=××
−1
2π
CC
fRC
CF F
SW F F
=×× ××
()
−205 1π.
RfC
R
ZI
I
11
22
=××
−
π
RfC
IPI
=××
1
21
π
CfL C V
VR
IC OUT OUT OSC
IN F
=×× × ×
×
2π
CfR
FLC F
=×××
1
2075π.
fRC
at f
ZFF LC1
1
2075=×× ×
π ..
R1 RF
COMP_
VOUT
VREF
R2
RI
CI
CF
CCF
-
+
gM
FB_
Figure 5. Type III Compensation Network
PGND_
DRAIN_
MAX5098A
VL
VDRV
V+
VOUT_
BST_/VDD_
COUT
SGND
PGND_
DRAIN_
SOURCE_
SOURCE_
FB_
Figure 6. Boost Application
fRC
at f
PII ZERO ESR1
1
2
=××π ,
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
24 ______________________________________________________________________________________
Target the unity-gain crossover frequency for:
2) Place a zero
where RF≥10kΩ.
3) Calculate CIfor a target crossover frequency, fC:
where ωC= 2πx fC:
4) Place a pole
5) Place the second zero
where
6) Place the second pole
the switching frequency.
Load-Dump Protection MOSFET
Select the external MOSFET with an adequate voltage
rating, VDSS, to withstand the maximum expected load-
dump input voltage. The on-resistance of the MOSFET,
RDS(ON), should be low enough to maintain a minimal
voltage drop at full load, limiting the power dissipation
of the MOSFET.
During regular operation, the power dissipated by the
MOSFET is:
PNORMAL = ILOAD2x RDS(ON)
where ILOAD is equal to the sum of both converters’
input currents.
The MOSFET operates in a saturation region during
load dump, with both high voltage and current applied.
Choose a suitable power MOSFET that can safely oper-
ate in the saturation region. Verify its capability to sup-
port the downstream DC-DC converters input current
during the load-dump event by checking its safe oper-
ating area (SOA) characteristics. Since the transient
peak power dissipation on the MOSFET can be very
high during the load-dump event, also refer to the ther-
mal impedance graph given in the data sheet of the
power MOSFET to make sure its transient power dissi-
pation is kept within the recommended limits.
Improving Noise Immunity
In applications where the MAX5098A is subject to noisy
environments, adjust the controller’s compensation to
improve the system’s noise immunity. In particular, high-
frequency noise coupled into the feedback loop causes
jittery duty cycles. One solution is to lower the crossover
frequency (see the
Compensation
section).
CC
fRC
CF F
SW F F
=×× ××
()
−205 1π.
fRC at
PFCF
2
1
212=××π /
RfC
R
LC I I
11
2
=××
−
π
fRC
at f
ZILC2
1
21
=××π .
RfC
IZERO RHP I
=××
1
2π,
fRC
at f
PII ZERO RHP1
1
2
=××π .
,
C
VDLC
RV
I
OSC C OUT OUT
CFIN
=
()
+
⎡
⎣
⎢⎤
⎦
⎥
−122
ω
ω
CfR
FLC F
=×××
1
2075π.
fRC
at f
ZFF LC1
1
2075=×× ×
π . .
ff
CZERO RHP
≤,
5
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 25
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching
losses and clean, stable operation. This is especially
true for dual converters where one channel can affect
the other. Refer to the MAX5099 Evaluation Kit data
sheet for a specific layout example. Use a multilayer
board whenever possible for better noise immunity.
Follow these guidelines for good PCB layout:
1) For SGND, use a large copper plane under the IC
and solder it to the exposed paddle. To effectively
use this copper area as a heat exchanger between
the PCB and ambient, expose this copper area on
the top and bottom side of the PCB. Do not make a
direct connection from the exposed pad copper
plane to SGND underneath the IC.
2) Isolate the power components and high-current
path from the sensitive analog circuitry.
3) Keep the high-current paths short, especially at the
ground terminals. This practice is essential for sta-
ble, jitter-free operation.
4) Connect SGND and PGND_ together at a single
point. Do not connect them together anywhere else
(refer to the MAX5099 Evaluation Kit data sheet for
more information).
5) Keep the power traces and load connections short.
This practice is essential for high efficiency. Use
thick copper PCBs (2oz vs. 1oz) to enhance full-
load efficiency.
6) Ensure that the feedback connection to COUT is
short and direct.
7) Route high-speed switching nodes (BST_/VDD_,
SOURCE_) away from the sensitive analog areas
(BYPASS, COMP_, and FB_). Use the internal PCB
layer for SGND as an EMI shield to keep radiated
noise away from the IC, feedback dividers, and
analog bypass capacitors.
Layout Procedure
1) Place the power components first, with ground ter-
minals adjacent (inductor, CIN_, and COUT_). Make
all these connections on the top layer with wide,
copper-filled areas (2oz copper recommended).
2) Group the gate-drive components (bootstrap
diodes and capacitors, and VLbypass capacitor)
together near the controller IC.
3) Make the DC-DC controller ground connections as
follows:
a) Create a small, signal ground plane underneath
the IC.
b) Connect this plane to SGND and use this plane
for the ground connection for the reference
(BYPASS), enable, compensation components,
feedback dividers, and OSC resistor.
c) Connect SGND and PGND_ together (this is the
only connection between SGND and PGND_).
Refer to the MAX5099 Evaluation Kit data sheet
for more information.
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
26 ______________________________________________________________________________________
BST2/VDD2
SOURCE2
SOURCE2
PGND1
FB2
COMP2
PGOOD2
EN2
SYNC
31
1
32
29
6
7
4
5
9
C6
D1
26
25
24
28
D2
C7
L1
C20
C9 R9
C8
R6
R22
R7
R8
R12 C11
C12 C13
19
18
21
VOUT1
PGND
SGND 20
17
CLOCK OUT
VL
VIN
VDRV
BST1/VDD1
SOURCE1
SOURCE1
CKO
FB1
COMP1
PGOOD1
EN1
FSEL_1
IN_HIGH
ON/OFF
GATE
V+
DRAIN1
DRAIN1
DRAIN2
DRAIN2
OSC
BYPASS
SGND
VDRV
V
L
12 22 23 2 3
11 10 13
C1
C19 C4 C15
816 15 1427
PGND2
30
VIN = 4.5V
TO 5.5V
MAX5098A
VIN
PGND
C14
D4
D5 C5
L2
C21
C17
R18 C16
R15
R23
R16
R17
VOUT2
PGND
SGND
VDRV
Figure 7. 4.5V to 5.5V Operation
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
______________________________________________________________________________________ 27
BST2/VDD2
SOURCE2
SOURCE2
PGND1
FB2
COMP2
PGOOD2
EN2
SYNC
31
1
32
29
6
7
4
5
9
C6
0.1μF
D1
26
25
24
28
D2
C7
22μF
C2
4.7μF
35V
L1
4.7μH
C20
33pF
C9
2700pF R9
12.7Ω
C8
270pF
R6
52.3kΩ
1%
R22
10kΩ
1% R7
10kΩ
1%
R8
976Ω
1%
R12
6.49Ω
C11
0.22μF
C12
2.2μF
C13
4.7μF
19
18
21
VOUT1
PGND
SGND 20
17
CLOCK OUT
VL
VDRV
BST1/VDD1
SOURCE1
SOURCE1
CKO
FB1
COMP1
PGOOD1
EN1
FSEL_1
IN_HIGH
ON/OFF
GATE
V+
DRAIN1
DRAIN1
DRAIN2
DRAIN2
OSC
BYPASS
SGND
VDRV
V
L
N1
R1
3.9kΩ
12 22 23 2 3
11 10 13
C1
22μF
100V
C3
150μF
25V
C19
1μF
25V
C4
10μF
25V
C15
10μF
25V
816
VDRV
15 1427
PGND2
30
VIN = 5.2V
TO 19V
VOUT1 =
5V AT 2A
R21
1Ω
MAX5098A
VIN
PGND
C14
0.1μF
D4
D5 C5
22μF
L2
4.7μH
C21
56pF
C17
2700pF
R18
7.15ΩC16
270pF
R15
37.4kΩ
1%
R23
10kΩ
1%
R16
12.1kΩ
1%
R17
976Ω
1%
VOUT2
PGND
SGND
VDRV
VOUT2 = 3.3V
AT 1A
Typical Application Circuit
MAX5098A
Dual, 2.2MHz, Automotive Buck or Boost
Converter with 80V Load-Dump Protection
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
28
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
MAX5098A
TQFN
(5mm x 5mm)
TOP VIEW
29
30
+
28
27
*EP
*EP = EXPOSED PAD.
12
11
13
DRAIN2
PGOOD2
EN2
FB2
COMP2
14
SOURCE2
DRAIN1
PGOOD1
EN1
SOURCE1
FB1
COMP1
12
CKO
4567
2324 22 20 19 18
PGND1
PGND2
VL
V+
IN_HIGH
ON/OFF
DRAIN2 DRAIN1
3
21
31 10
BST2/VDD2 GATE
32 9
SOURCE2 SYNC
VDRV
26 15 SGND
BST1/VDD1
25 16 BYPASS
OSC FSEL_1
8
17
SOURCE1
Pin Configuration Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information, go to
www.maxim-ic.com/packages.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
32 TQFN T3255+4 21-0140
