General Description
The MAX5090A/B/C easy-to-use, high-efficiency, high-
voltage step-down DC-DC converters operate from an input
voltage up to 76V, and consume only 310µA quiescent
current at no load. This pulse-width-modulated (PWM)
converter operates at a fixed 127kHz switching frequency at
heavy loads, and automatically switches to pulse-skipping
mode to provide low quiescent current and high efficiency
at light loads. The MAX5090 includes internal frequency
compensation simplifying circuit implementation. The
device can also be synchronized with external system clock
frequency in a noise-sensitive application. The MAX5090
uses an internal low on-resistance and a high-voltage DMOS
transistor to obtain high efficiency and reduce overall system
cost. This device includes undervoltage lockout, cycle-
by-cycle current limit, hiccup-mode output short-circuit
protection, and overtemperature shutdown.
The MAX5090 delivers up to 2A output current. External
shutdown is included, featuring 19µA (typ) shutdown
current. The MAX5090A/MAX5090B versions have fixed
output voltages of 3.3V and 5V, respectively, while the
MAX5090C features an adjustable 1.265V to 11V output
voltage.
The MAX5090 is available in a space-saving 16-pin
thin QFN package (5mm x 5mm) and operates over the
automotive temperature range (-40°C to +125°C).
Applications
●Industrial
●Distributed Power
Features
●Wide Input Voltage Range: 6.5V to 76V
●Fixed (3.3V, 5V) and Adjustable (1.265V to 11V)
Output-Voltage Versions
●2A Output Current
●Efficiency Up to 92%
● Internal 0.26Ω High-Side DMOS FET
●310µA Quiescent Current at No Load
●19µA Shutdown Current
●Internal Frequency Compensation
●Fixed 127kHz Switching Frequency
●External Frequency Synchronization
●Thermal Shutdown and Short-Circuit Current Limit
●-40°C to +125°C Automotive Temperature Range
●6-Pin (5mm x 5mm) Thin QFN Package
●Capable of Dissipating 2.67W at +70°C
Ordering Information continued at end of data sheet.
19-3872; Rev 1; 9/14
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PART TEMP
RANGE
PIN-
PACKAGE
OUTPUT
VOLTAGE
(V)
MAX5090AATE+ -40°C to +125°C 16 TQFN-EP* 3.3
MAX5090AATE -40°C to +125°C 16 TQFN-EP* 3.3
MAX5090BATE+ -40°C to +125°C 16 TQFN-EP* 5.0
MAX5090BATE -40°C to +125°C 16 TQFN-EP* 5.0
PGND
BST
LX
VIN
SGND
FB
VOUT
5V/2A
VD
100µH
CBST
0.22µF
3.3µF
ON/OFF COUT
100µF
SS
SYNC
D1
PDS5100H
DRAIN
CSS
0.047µF
CIN
68µF CBYPASS
0.47µF
RIN
10Ω
VIN
7.5V TO 76V
MAX5090B 15
16
14
13
6
5
7
LX
VIN
8
LX
N.C.
ON/OFF
PGND
1 2
DRAIN
4
12
EP
11 9
N.C.
N.C.
FB
SS
SYNC
VD
MA5090
BST SGND
3
10
DRAIN
TQFN
TOP VIEW
MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converters
Typical Operating Circuit Pin Conguration
Ordering Information
EVALUATION KIT AVAILABLE
(Voltages referenced to PGND, unless otherwise specified.)
VIN, DRAIN ............................................................ -0.3V to +80V
SGND, PGND. ...................................................... -0.3V to +0.3V
LX ...............................................................-0.8V to (VIN + 0.3V)
BST ..............................................................-0.3V to (VIN + 10V)
BST to LX ..............................................................-0.3V to +10V
ON/OFF ......................................................-0.3V to (VIN + 0.3V)
VD, SYNC .............................................................-0.3V to +12V
SS .............................................................................. -0.3 to +4V
FB
MAX5090A/MAX5090B .....................................-0.3V to +15V
MAX5090C ................ 1mA (internally clamped to +2V, -0.3V)
VOUT Short-Circuit Duration ......................................Continuous
VD Short-Circuit Duration .......................................... Continuous
Continuous Power Dissipation (TA = +70°C)*
16-Pin TQFN (derate 33.3mW/°C above +70°C) ........2.667W
Operating Junction 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
*As per JEDEC 51 Standard Multilayer Board.
(VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at
TA = +25°C. See the Typical Operating Circuit.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage Range VIN 6.5 76.0 V
Undervoltage Lockout UVLO VIN rising 5.70 6.17 6.45 V
UVLO Hysteresis UVLOHYS 0.5 V
Output Voltage VOUT
MAX5090A VIN = 6.5V to 76V, IOUT = 0 to 2A 3.20 3.3 3.39
VMAX5090B VIN = 7.5V to 76V, IOUT = 0 to 2A 4.85 5.0 5.15
MAX5090B VIN = 7V to 76V, IOUT = 0 to 1A 4.85 5.0 5.15
Output Voltage Range VOUT MAX5090C only 1.265 11.000 V
Feedback Voltage VFB MAX5090C, VIN = 6.5V to 76V 1.191 1.228 1.265 V
Efciency η
MAX5090A VIN = 12V, IOUT = 1A 80
%MAX5090B VIN = 12V, IOUT = 1A 88
MAX5090C VIN = 12V, VOUT = 5V, IOUT = 1A 88
Quiescent Supply Current
(Note 2) IQ
MAX5090A VIN = 6.5V to 28V 310 550
µAMAX5090B VIN = 7V to 28V 310 550
MAX5090C VIN = 6.5V to 28V 310 550
Quiescent Supply Current
(Note 2) IQ
MAX5090A VIN = 6.5V to 40V 310 570
µAMAX5090B VIN = 7V to 40V 310 570
MAX5090C VIN = 6.5V to 40V 310 570
Quiescent Supply Current
(Note 2) IQ
MAX5090A VIN = 6.5V to 76V 310 650
µA
MAX5090B VIN = 7V to 76V 310 650
MAX5090C VIN = 6.5V to 76V 310 650
Shutdown Current ISHDN VON/OFF = 0V, VIN = 14V 19 45 µA
SOFT-START
Default Internal Soft-Start
Period CSS = 0 700 µs
Soft-Start Charge Current ISS 4.5 10 16.0 µA
Soft-Start ReferenceVoltage VSS(REF) 1.23 1.46 1.65 V
MAX5090A/B/C 2A, 76V, High-Efciency MAXPower
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Absolute Maximum Ratings
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.
Electrical Characteristics
(VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at
TA = +25°C. See the Typical Operating Circuit.) (Note 1)
Note 1: All limits at -40°C are guaranteed by design, not production tested.
Note 2: For total current consumption during switching (at no load), also see the Typical Operating Characteristics.
Note 3: Switch current at which the current-limit circuit is activated.
Note 4: Limits are guaranteed by design.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INTERNAL SWITCH/CURRENT LIMIT
Peak Switch Current Limit ILIM (Note 3) 2.4 3.3 5.0 A
Switch Leakage Current IOL VIN = 76V, VON/OFF = 0V, VLX = 0V -10 +10 µA
Switch On-Resistance RDS(ON) ISWITCH = 1A 0.26 0.4 Ω
PFM Threshold IPFM Minimum switch current in any cycle 1 60 300 mA
PFM Threshold IPFM Minimum switch current in any cycle at
TJ ≤ +25°C (Note 4) 14 300 mA
FB Input Bias Current IBMAX5090C, VFB = 1.2V -150 +0.1 +150 nA
ON/OFF CONTROL INPUT
ON/OFF Input-Voltage
Threshold VON/OFF Rising trip point 1.180 1.38 1.546 V
ON/OFF Input-Voltage
Hysteresis VHYST 100 mV
ON/OFF Input Current ION/OFF VON/OFF = 0V to VIN 10 100 nA
OSCILLATOR/SYNCHRONIZATION
Oscillator Frequency f0SC 106 127 150 kHz
Synchronization fSYNC 119 200 kHz
Maximum Duty Cycle DMAX VIN = 6.5V to 76V, VOUT ≤ 11V 80 95 %
SYNC High-Level Voltage 2.0 V
SYNC Low-Level Voltage 0.8 V
SYNC Minimum Pulse Width 350 ns
SYNC Input Leakage -1 +1 µA
INTERNAL VOLTAGE REGULATOR
Regulator Output Voltage VDVIN = 9V to 76V, IOUT = 0 7.0 7.8 8.4 V
Dropout Voltage 6.5V ≤ VIN ≤ 8.5V, IOUT = 15mA 0.5 V
Load Regulation ∆VD/∆IVD 0 to 15mA 10 Ω
PACKAGE THERMAL CHARACTERISTICS
Thermal Resistance
(Junction to Ambient) θJA TQFN package (JEDEC 51) 30 °C/W
THERMAL SHUTDOWN
Thermal-Shutdown Junction
Temperature TSH Temperature rising +175 °C
Thermal-Shutdown
Hysteresis THYST 20 °C
MAX5090A/B/C 2A, 76V, High-Efciency MAXPower
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Electrical Characteristics (continued)
(VIN = 12V, VON/OFF =12V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical
Operating Circuit, if applicable.)
4.85
4.90
4.95
5.00
5.05
5.10
5.15
-50 0-25 25 50 75 100 125 150
VOUT vs. TEMPERATURE
(MAX5090BATE, VOUT = 5V)
MAX5090 toc02
AMBIENT TEMPERATURE (°C)
VOUT (V)
IOUT = 0
IOUT = 2A
3.20
3.26
3.24
3.22
3.30
3.28
3.38
3.36
3.34
3.32
3.40
6.5 16 26 36 46 56 66 76
LINE REGULATION
(MAX5090AATE, VOUT = 3.3V)
MAX5090 toc03
VIN (V)
VOUT (V)
IOUT = 0
IOUT = 2A
4.85
4.95
4.90
5.05
5.00
5.10
5.15
6.5 36 4616 26 56 66 76
LINE REGULATION
(MAX5090BATE, VOUT = 5V)
MAX5090 toc04
VIN (V)
VOUT (V)
IOUT = 0
IOUT = 2A
ILOAD (mA)
V
OUT
(V)
LOAD REGULATION
(MAX5090AATE, VOUT = 3.3V)
3.38
3.40
3.32
3.34
3.36
0.1 1 10 100 1000 10,000
MAX5090 toc05
3.28
3.30
3.22
3.24
3.26
3.20
VIN = 76V
VIN = 24V
VIN = 6.5V
ILOAD (mA)
VOUT (V)
LOAD REGULATION
(MAX5090BATE, VOUT = 5V)
5.15
5.10
5.05
5.00
MAX5090 toc06
4.95
4.90
4.85
0.1 1 10 100 1000
10,000
VIN = 24V
VIN = 76V
VIN = 6.5V
0
30
20
10
40
50
60
70
80
90
100
0 800400 1200 1600 2000
EFFICIENCY vs. LOAD CURRENT
(MAX5090AATE, VOUT = 3.3V)
MAX5090 toc07
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 76V
VIN = 48V
VIN = 24V
VIN = 12V
VIN = 6.5V
3.20
3.24
3.22
3.28
3.26
3.32
3.30
3.34
3.38
3.36
3.40
-50 0 25-25 50 75 100 125 150
VOUT vs. TEMPERATURE
(MAX5090AATE, VOUT = 3.3V)
MAX5090 toc01
AMBIENT TEMPERATURE (°C)
VOUT (V)
IOUT = 0
IOUT = 2A
0
30
20
10
40
50
60
70
80
90
100
0 800400 1200 1600 2000
EFFICIENCY vs. LOAD CURRENT
(MAX5090BATE, VOUT = 5V)
MAX5090 toc08
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 6.5V
VIN = 76V
VIN = 48V
VIN = 24V
VIN = 12V
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-50 0-25 25 50 75 100 125 150
OUTPUT CURRENT LIMIT
vs. TEMPERATURE (MAX5090AATE)
MAX5090 toc09
AMBIENT TEMPERATURE (°C)
OUTPUT CURRENT LIMIT (A)
VOUT = 3.3V
5% DROP IN VOUT
PULSED OUTPUT LOAD
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Typical Operating Characteristics
(VIN = 12V, VON/OFF =12V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical
Operating Circuit, if applicable.)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-50 0-25 25 50 75 100 125 150
OUTPUT CURRENT LIMIT vs. TEMPERATURE
(MAX5090BATE)
MAX5090 toc010
AMBIENT TEMPERATURE (°C)
OUTPUT CURRENT LIMIT (A)
VOUT = 5V
5% DROP IN VOUT
PULSED OUTPUT LOAD
1.0
3.0
2.0
5.0
4.0
6.0
7.0
6.5 36 4616 26 56 66 76
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE
(MAX5090AATE)
MAX5090 toc11
INPUT VOLTAGE (V)
OUTPUT CURRENT LIMIT (A)
VOUT = 3.3V
5% DROP IN VOUT
PULSED OUTPUT LOAD
1.0
3.0
2.0
5.0
4.0
6.0
7.0
6.5 36 4616 26 56 66 76
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE
(MAX5090BATE)
MAX5090 toc12
INPUT VOLTAGE (V)
OUTPUT CURRENT LIMIT (A)
VOUT = 5V
5% DROP IN VOUT
PULSED OUTPUT LOAD
300
350
400
450
500
550
600
-50 0-25 25 50 75 100 125 150
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE
(MAX5090AATE)
MAX5090 toc13
AMBIENT TEMPERATURE (°C)
NO-LOAD SUPPLY CURRENT (µA)
VOUT = 3.3V
300
400
350
500
450
550
600
6.5 36 4616 26 56 66 76
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
(MAX5090AATE)
MAX5090 toc14
INPUT VOLTAGE (V)
NO-LOAD SUPPLY CURRENT
VOUT = 3.3V
10
14
22
18
26
30
-50 0 25-25 50 100 125 150 175
SHUTDOWN CURRENT vs. TEMPERATURE
(MAX5090AATE)
MAX5090 toc15
AMBIENT TEMPERATURE (°C)
SHUTDOWN CURRENT (µA)
VOUT = 3.3V
0
10
5
25
20
15
40
35
30
45
6.5 36 4616 26 56 66 76
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
MAX5090 toc16
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (µA)
VOUT = 3.3V
0
3
6
9
11
13
5 9 107 86 11 11.5 12 12.5 13
OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX5090 toc17
VIN (V)
V
OUT
(V)
IOUT = 0A
IOUT = 1A
IOUT = 2A
MAX5090CATE
VOUT = 11V
VON/OFF = VIN
MAX5090 toc18
LOAD-TRANSIENT RESPONSE
(MAX5090AATE)
VOUT = 3.3V
A: VOUT, 200mV/div, AC-COUPLED
B: IOUT, 1A/div, 1A TO 2A
400µs/div
A
B
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Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF =12V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical
Operating Circuit, if applicable.)
MAX5090 toc19
LOAD-TRANSIENT RESPONSE
(MAX5090AATE)
VOUT = 3.3V
A: VOUT, 200mV/div, AC-COUPLED
B: IOUT, 500mA/div, 0.1A TO 1A
400µs/div
A
B
LX WAVEFORMS
(MAX5090AATE)
MAX5090 toc20
VOUT = 3.3V
A
B
A: SWITCH VOLTAGE (LX PIN), 20mV/div (VIN = 48V)
B: INDUCTOR CURRENT, 2A/div (I0 = 2A)
4µs/div
0
MAX5090 toc21
LX WAVEFORMS
(MAX5090AATE)
VOUT = 3.3V
A: SWITCH VOLTAGE, 20V/div (VIN = 48V)
B: INDUCTOR CURRENT, 200mA/div (I0 = 75mA)
4µs/div
A
B
MAX5090 toc22
LX WAVEFORM
(MAX5090AATE)
VOUT = 3.3V
A: SWITCH VOLTAGE, 20V/div (VIN = 48V)
B: INDUCTOR CURRENT, 200mA/div (IOUT = 0)
4µs/div
A
B
MAX5090 toc23
STARTUP WAVEFORM
(IOUT = 0)
A: VON/OFF, 2V/div
B: VOUT, 1V/div
4ms/div
A
B
CSS = 0.047µF
MAX5090 toc24
STARTUP WAVEFORM
(IOUT = 2A)
A: VON/OFF, 2V/div
B: VOUT, 1V/div
4ms/div
A
B
CSS = 0.047µF
1.0
3.0
2.0
5.0
4.0
6.0
7.0
6.5 36 4616 26 56 66 76
PEAK SWITCH CURRENT
vs. INPUT VOLTAGE
MAX5090 toc25
INPUT VOLTAGE (V)
PEAK SWITCH CURRENT (A)
MAX5090AATE
VOUT = 3.3V
5% DROP IN VOUT
PULSED OUTPUT LOAD
MAX5090 toc26
SYNCHRONIZATION
fSYNC = 119kHz
SYNC
2V/div
LX
10V/div
2µs/div
MAX5090 toc27
fSYNC = 200kHz
SYNCHRONIZATION
1µs/div
SYNC
2V/div
LX
10V/div
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Typical Operating Characteristics (continued)
Detailed Description
The MAX5090 step-down DC-DC converter operates from
a 6.5V to 76V input voltage range. A unique voltage-mode
control scheme with voltage feed-forward and an internal
switching DMOS FET provides high efficiency over a wide
input voltage range. This pulse-width-modulated convert-
er operates at a fixed 127kHz switching frequency or can
be synchronized with an external system clock frequency.
The device also features automatic pulse-skipping mode
to provide high efficiency at light loads. Under no load,
the MAX5090 consumes only 310µA, and in shutdown
mode, consumes only 20µA. The MAX5090 also features
undervoltage-lockout, hiccup-mode output short-circuit
protection and thermal shutdown.
ON/OFF/Undervoltage Lockout (UVLO)
Use the ON/OFF function to program the external UVLO
threshold at the input. Connect a resistive voltage-divider
from VIN to SGND with the center node to ON/OFF, as
shown in Figure 1. Calculate the threshold value by using
the following formula:
UVLO(TH)
R1
V 1 1.38
R2
=+×
Set the external VUVLO(TH) to greater than 6.45V. The
maximum recommended value for R2 is less than 1MΩ.
ON/OFF is a logic input and can be safely driven to the full
VIN range. Connect ON/OFF to VIN for automatic startup.
Drive ON/OFF to ground to shut down the MAX5090.
Shutdown forces the internal power MOSFET off, turns off
all internal circuitry, and reduces the VIN supply current to
20µA (typ). The ON/OFF rising threshold is 1.546V (max).
Before any operation begins, the voltage at ON/OFF must
exceed 1.546V. The ON/OFF input has 100mV hysteresis.
If the external UVLO threshold-setting divider is not used,
an internal undervoltage-lockout feature monitors the
supply voltage at VIN and allows the operation to start
when VIN rises above 6.45V (max). The internal UVLO
rising threshold is set at 6.17V with 0.5V hysteresis.
The VIN and VON/OFF voltages must be above 6.5V and
1.546V, respectively, for proper operation.
PIN NAME FUNCTION
1, 2 LX Source Connection of Internal High-Side Switch
3 BST Boost Capacitor Connection. Connect a 0.22µF ceramic capacitor from BST to LX.
4 VIN Input Voltage. Bypass VIN to SGND with a low-ESR capacitor as close as possible to the device.
5 VD Internal Regulator Output. Bypass VD to PGND with a 3.3µF/10V or greater ceramic capacitor.
6 SYNC Synchronization Input. Connect SYNC to an external clock for synchronization. Connect to SGND to
select the internal 127kHz switching frequency.
7 SS Soft-Start Capacitor Connection. Connect an external capacitor from SS to SGND to adjust the
soft-start time.
8 FB
Output Sense Feedback Connection.
For xed output voltage (MAX5090A/MAX5090B), connect FB to VOUT.
For adjustable output voltage (MAX5090C), use an external resistive voltage-divider to set VOUT.
VFB regulating set point is 1.228V.
9 ON/OFF Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for
normal operation. Connect ON/OFF to VIN with short leads for always-on operation.
10 SGND Signal Ground. SGND must be connected to PGND for proper operation.
11, 15, 16 N.C. No Connection. Not internally connected.
12 PGND Power Ground
13, 14 DRAIN Internal High-Side Switch Drain Connection
— EP Exposed Pad. Solder EP to SGND plane to aid in heat dissipation. Do not use as the only electrical
ground connection.
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Pin Description
MAX5090
REGULATOR
(FOR ANALOG)
ENABLE
LX
BST
VIN
ON/OFF
VREF
REGULATOR
(FOR DRIVER) OSC RAMP
IREF-PFM
IREF-LIM
CPFM
1.38V
CILIM
FB
EAMP
THERMAL
SHUTDOWN
CPWM
VD
PGND
RAMP
CLK
CONTROL
LOGIC
TYPE 3
COMPENSATION
SGND
x1
*RH
DRAIN
SYNC
SS
MIN
SRAMP
MUX
SRMP
SCK
*RL
CLKI RMP
N
HIGH-SIDE
CURRENT SENSE
*RH = 0Ω AND RL = ∞ FOR MAX5090C
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Simplied Functional Diagram
Boost High-Side Gate Drive (BST)
Connect a flying bootstrap capacitor between LX and
BST to provide the gate-drive voltage to the high-side
n-channel DMOS switch. The capacitor is alternately
charged from the internally regulated output-voltage
VD and placed across the high-side DMOS driver. Use
a 0.22µF, 16V ceramic capacitor located as close as
possible to the device.
On startup, an internal low-side switch connects LX to
ground and charges the BST capacitor to (VD - VDIODE).
Once the BST capacitor is charged, the internal low-
side switch is turned off and the BST capacitor voltage
provides the necessary enhancement voltage to turn on
the high-side switch.
Synchronization (SYNC)
SYNC controls the oscillator frequency. Connect SYNC to
SGND to select 127kHz operation. Use the SYNC input
to synchronize to an external clock. SYNC has a guaran-
teed 119kHz to 200kHz frequency range when using an
external clock.
When SYNC is connected to SGND, the internal clock is
used to generate a ramp with the amplitude in proportion
to VIN and the period corresponding to the internal clock
frequency to modulate the duty cycle of the high-side
switch.
If an external clock (SYNC clock) is applied at SYNC
for four cycles, the MAX5090 selects the SYNC clock.
The MAX5090 generates a ramp (SYNC ramp) with
the amplitude in proportion to VIN and the period
corresponding to the SYNC clock frequency. The MAX5090
initially blanks the SYNC ramp for 375µs (typ) to allow the
ramp to reach its target amplitude (proportion to the VIN
supply). After the SYNC blanking time, the SYNC ramps
and the SYNC clock switches to the PWM controller
and replaces the internal ramp and the internal clock,
respectively. If the SYNC clock is removed for three
internal clock cycles, the internal clock and the internal
ramp switch back to the PWM controller.
The minimum pulse-width requirement for the external
clock is 350ns, and if the requirement is not met, the
MAX5090 could ignore the clock as a noisy bounce.
Soft-Start (SS)
The MAX5090 provides the flexibility to externally
program a suitable soft-start time for a given application.
Connect an external capacitor from SS to SGND to use
the external soft-start. Soft-start gradually ramps up the
reference voltage seen by the error amplifier to control
the output’s rate of rise and reduce the input surge current
during startup. For soft-start time longer than 700µs, use
the following equation to calculate the soft-start capacitor
(CSS) required for the soft-start time (tSS):
6
SS
SS
10 10 t
C
1.46
−
××
=
where tSS > 700µs and CSS is in Farads.
The MAX5090 also provides an internal soft-start (700µs,
typ) with a current source to charge an internal capacitor
to rise up to the bandgap reference voltage. The internal
soft-start voltage will eventually be pulled up to 3.4V. The
internal soft-start reference also feeds to the error ampli-
fier. The error amplifier takes the lowest voltage among
SS, the internal soft-start voltage, and the bandgap
reference voltage as the input reference for VOUT.
Soft-start occurs when power is first applied and when
the device exits shutdown. The MAX5090 also goes
through soft-start when coming out of thermal-overload
protection. During a soft-start, if the voltage at SS (VSS)
is charged up to 1.46V in less than 700µs, the MAX5090
takes its default internal soft-start (700µs) to ramp up as
its reference. After the SS and the internal soft-start ramp
up over the bandgap reference, the error amplifier takes
the bandgap reference.
Thermal-Overload Protection
The MAX5090 features integrated thermal-overload
protection. Thermal-overload protection limits power
dissipation in the device, and protects the device from a
thermal overstress. When the die temperature exceeds
+175°C, an internal thermal sensor signals the shut-
down logic, turning off the internal power MOSFET,
resetting the internal soft-start, and allowing the IC
to cool. The thermal sensor turns the internal power
MOSFET back on after the IC’s die temperature cools
down to +155°C, resulting in a pulsed output under
continuous thermal-overload conditions.
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Figure 1. Fixed Output-Voltage Configuration
Figure 2. Adjustable Output-Voltage Configuration
PGND
BST
LX
VIN
SGND
FB
VOUT
3.3V, 2A
R1
VD
0.22µF
100µH
3.3µF
R2
ON/OFF COUT
100µF
SS
SYNC
D1
PDS5100H
DRAIN
0.047µF
CIN
68µF CBYPASS
0.47µF
RIN
10Ω
VIN
6.5V TO 76V
MAX5090A
MAX5090C
PGND
BST
LX
VIN
SGND
FB
VD
SS
SYNC
DRAIN
VOUT
5.25V, 2A
0.22µF
100µH
3.3µF
COUT
100µF
D1
PDS5100H
0.047µF
CIN
68µF
VIN
7.5V TO 76V
CBYPASS
0.47µF
RIN
10Ω
R4
R3
ON/OFF
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Thermal-overload protection is intended to protect the
MAX5090 in the event of a fault condition. For normal
circuit operation, do not exceed the absolute maximum
junction temperature rating of TJ = +150°C.
Setting the Output Voltage
The MAX5090A/MAX5090B have preset output voltages
of 3.3V and 5.0V, respectively. Connect FB to VOUT for
the preset output voltage (Figure 1).
The MAX5090C offers an adjustable output voltage. Set
the output voltage with a resistive divider connected from
the circuit’s output to ground (Figure 2). Connect the
center node of the divider to FB. Choose R4 less than
15kΩ, then calculate R3 as follows:
OUT
(V 1.228)
R3 R4
1.228
−
= ×
The MAX5090 features internal compensation for
optimum closed-loop bandwidth and phase margin.
Because of the internal compensation, the output must
be sensed immediately after the primary LC.
Inductor Selection
The MAX5090 is a fixed-frequency converter with fixed
internal frequency compensation. The internal fixed
compensation assumes a 100µH inductor and 100µF
output capacitor with 50mΩ ESR. It relies on the location
of the double LC pole and the ESR zero frequency for
proper closed-loop bandwidth and the phase margin at the
closed-loop unity-gain frequency. See Table 2 for proper
component values. Usually, the choice of an inductor is
guided by the voltage difference between VIN and VOUT,
the required output current, and the operating frequency
of the circuit. However, use the recommended inductors
in Table 2 to ensure stable operation with optimum band-
width.
Use an inductor with a maximum saturation current rating
greater than or equal to the maximum peak current limit
(5A). Use inductors with low DC resistance for a higher
efficiency converter.
Selecting a Rectier
The MAX5090 requires an external Schottky rectifier as
a freewheeling diode. Connec
t this rectifier close to the
device using short leads and short PCB traces. The recti-
fier diode must fully conduct the inductor current when the
power FET is off to have a full rectifier function. Choose a
rectifier with a contin
uous current rating greater than the
highest expected output current. Use a rectifier with a
voltage rating greater than the maximum expected input
voltage, VIN. Use a low forward-voltage Schottky rectifier
for proper operation and high efficiency. Avoid higher than
necessary reverse-voltage Schottky rectifiers that have
higher forward-voltage drops. Use a Schottky rectifier with
forward-voltage drop (VF) less than 0.55V and 0.45V at +25°C
and +125°C, respectively, and at maximum load current to
avoid forward biasing of the internal parasitic body diode
(LX to ground). See Figure 3 for forward-voltage drop vs.
temperature of the internal body diode of the MAX5090.
Internal parasitic body-diode conduction may cause improper
operation, excessive junction temperature rise, and thermal
shutdown. Use Table 1 to choose the proper rectifier at
different input voltages and output current.
Input Bypass Capacitor
The discontinuous input current waveform of the buck
converter causes large ripple currents in the input capaci-
tor. The switching frequency, peak inductor current, and
the allowable peak-to-peak voltage ripple reflecting back
to the source dictate the capacitance requirement. The
MAX5090 high-switching frequency allows the use of
smaller-value input capacitors.
The input ripple is comprised of ∆VQ (caused by the
capacitor discharge) and ∆VESR (caused by the ESR
of the capacitor). Use low-ESR aluminum electrolytic
capacitors with high-ripple current capability at the input.
Assuming that the contribution from the ESR and capaci-
tor discharge is equal to 90% and 10%, respectively,
Table 1. Diode Selection
VIN (V) DIODE PART
NUMBER MANUFACTURER
6.5 to 36
B340LB Diodes Inc.
RB051L-40 Central Semiconductor
MBRS340T3 ON Semiconductor
6.5 to 56
MBRM560 Diodes Inc.
RB095B-60 Central Semiconductor
MBRD360T4 ON Semiconductor
6.5 to 76 50SQ80 IR
PDS5100H Diodes Inc.
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calculate the input capacitance and the ESR required for
a specified ripple using the following equations:
ESR
IN L
OUT
OUT
IN Q SW
V
ESR I
I2
I D(1 D)
CVf
∆
=∆
+
×−
=∆×
where:
IN OUT OUT
LIN SW
OUT
IN
(V V ) V
IVf L
V
DV
−×
∆= ××
=
IOUT is the maximum output current of the converter and
fSW is the oscillator switching frequency (127kHz). For
example, at VIN = 48V, VOUT = 3.3V, the ESR and input
capacitance are calculated for the input peak-to-peak
ripple of 100mV or less, yielding an ESR and capacitance
value of 40mΩ and 100µF, respectively.
Low-ESR ceramic multilayer chip capacitors are
recommended for size-optimized application. For ceramic
capacitors, assume the contribution from ESR and capac-
itor discharge is equal to 10% and 90%, respectively.
The input capacitor must handle the RMS ripple current
without significant rise in the temperature. The maximum
capacitor RMS current occurs at approximately 50% duty
cycle. Ensure that the ripple specification of the input
capacitor exceeds the worst-case capacitor RMS ripple
current. Use the following equations to calculate the input
capacitor RMS current:
22
CRMS PRMS AVGin
I II= −
where:
22
PK DC
PRMS PK DC I I
OUT OUT
AVGin IN
L
PK OUT
L
DC OUT
OUT
IN
D
I (I I )
3
V I
IV
I
II
2
I
II 2
V
DV
+×
=+×
×
=×η
∆
= +
∆
= −
=
IPRMS is the input switch RMS current, IAVGin is the input
average current, and h is the converter efficiency.
The ESR of the aluminum electrolytic capacitor increases
significantly at cold temperatures. Use a 1µF or greater value
ceramic capacitor in parallel with the aluminum electrolytic
input capacitor, especially for input voltages below 8V.
Output Filter Capacitor
The output capacitor (COUT) forms double pole with
the inductor and a zero with its ESR. The MAX5090’s
internal fixed compensation is designed for a 100µF
capacitor, and the ESR must be from 20mΩ to 100mΩ. The
use of an aluminum or tantalum electrolytic capacitor is
recommended. See Table 2 to choose an output capacitor
for stable operation.
The output ripple is comprised of ∆VOQ (caused by the
capacitor discharge), and ∆VOESR (caused by the ESR
of the capacitor). Use low-ESR tantalum or aluminum
electrolytic capacitors at the output. Use the following
equations to calculate the contribution of output capaci-
tance and its ESR on the peak-to-peak output rip voltage:
OESR L
L
OQ
OUT SW
V I ESR
I
V8C f
∆ =∆×
∆
∆≈
××
The MAX5090 has a programmable soft-start time (t
SS
).
The output rise time is directly proportional to the output
capacitor, output voltage, and the load. The output rise time
also depends on the inductor value and the current-limit
threshold. It is important to keep the output rise time at
startup the same as the soft-start time (t
SS
) to avoid output
Figure 3. Forward-Voltage Drop vs. Temperature of the Internal
Body Diode of MAX5090
0
100
200
300
400
500
600
700
800
-40 10025 125 150
TEMPERATURE (°C)
VF_D1 (mV)
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overshoot. Large output capacitors take longer than the
programmed soft-start time (t
SS
) and cause error-amplifier
saturation. This results in output overshoot. Use greater
than 2ms soft-start time for a 100µF output capacitor.
In a dynamic-load application, the allowable deviation of
the output voltage during the fast transient load dictates
the output capacitance value and the ESR. The output
capacitors supply 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 converter. The resistive drop across the capaci-
tor ESR and capacitor discharge cause a voltage droop
during a step-load. Use a combination of low-ESR
tantalum and ceramic capacitors for better transient
load and ripple/noise performance. Use the following
equations to calculate the deviation of output voltage due
to the ESR and capacitance value of the out capacitor:
OESR STEP OUT
STEP RESPONSE
OQ
OUT
V I ESR
It
VC
∆=×
×
∆=
where ISTEP is the load step and tRESPONSE is the
response time of the controller. Controller response time
is approximately one-third of the reciprocal of the closed-
loop unity-gain bandwidth, 20kHz typically.
Board Layout Guidelines
1) Minimize ground noise by connecting the anode of the
Schottky rectifier, the input bypass capacitor ground
lead, and the output filter capacitor ground lead to a
large PGND plane.
2) Minimize lead lengths to reduce stray capacitance,
trace resistance, and radiated noise. In particular,
place the Schottky rectifier diode right next to the
device. Also, place the BST and VD bypass capacitors
very close to the device.
3) Connect the exposed pad of the IC to the SGND plane.
Do not make a direct connection between the exposed
pad plane and SGND (pin 7) under the IC. Connect
the exposed pad and pin 7 to the SGND plane sepa-
rately. Connect the ground connection of the feedback
resistive divider, ON/OFF threshold resistive divider,
and the soft-start capacitor to the SGND plane.
Connect the SGND plane and PGND plane at one
point near the input bypass capacitor at VIN.
4) Use large SGND plane as a heatsink for the MAX5090.
Use large PGND and LX planes as heatsinks for the
rectifier diode and the inductor.
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Table 2. Typical External Components Selection (Circuit of Figure 4)
Figure 4. Fixed Output Voltage
VIN (V) VOUT (V) IOUT (A) EXTERNAL COMPONENTS
6.5 to 76 3.3 2
MAX5090AATE
CIN = 2 x 68µF/100V EEVFK2A680Q, Panasonic
CBYPASS = 0.47µF/100V, GRM21BR72A474KA, Murata
COUT = 220µF/6.3V 6SVP220MX, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1%, 0603
D1 = PDS5100H, Diodes Inc.
L1 = 47µH, DO5022P-473
7.5 to 76 5 2
MAX5090BATE
CIN = 2 x 68µF/100V EEVFK2A680Q, Panasonic
CBYPASS = 0.47µF/100V, GRM21BR72A474KA, Murata
COUT = 100µF/6.3V 6SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1%, 0603
D1 = PDS5100H, Diodes Inc.
L1 = 47µH, DO5022P-473
PGND
BST
LX
VIN
VIN
SGND
FB
VOUT
R1
VD
L1
CBST
3.3µF
R2
COUT
SS
SYNC
D1
DRAIN
CSS
CIN
CBYPASS
RIN
MAX5090B
ON/OFF
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Application Circuit
Table 2. Typical External Components Selection (Circuit of Figure 4) (continued)
Table 3. Component Suppliers
SUPPLIER WEBSITE
AVX www.avxcorp.com
Coilcraft www.coilcraft.com
Diodes Incorporated www.diodes.com
Panasonic www.panasonic.com
Sanyo www.sanyo.com
TDK www.component.tdk.com
Vishay www.vishay.com
VIN (V) VOUT (V) IOUT (A) EXTERNAL COMPONENTS
6.5 to 40 3.3 2
MAX5090AATE
CIN = 330µF/50V EEVFK1H331Q, Panasonic
CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata
COUT = 100µF/6.3V 6SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1%, 0603
D1 = B360, Diodes Inc.
L1 = 100µH, DO5022P-104
7.5 to 40 5 2
MAX5090BATE
CIN = 330µF/50V EEVFK1H331Q, Panasonic
CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata
COUT = 100µF/6.3V 6SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1%, 0603
D1 = B360, Diodes Inc
L1 = 100µH, DO5022P-104
15 to 40 11 2
MAX5090CATE (VOUT programmed to 11V)
CIN = 330μF/50V EEVFK1H331Q, Panasonic
CBYPASS = 0.47μF/50V, GRM21BR71H474KA, Murata
COUT = 100μF/16V 16SVP100M, Sanyo
CBST = 0.22μF/16V, GRM188R71C224K, Murata
R1 = 910kΩ
R2 = 100kΩ
R3 = 88.2kΩ, ±1% (0603)
R4 = 10kΩ, ±1% (0603)
RIN = 10Ω, ±1% (0603)
D1 = B360, Diodes Inc.
L1 = 100μH, DO5022P-104
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Figure 5. Load-Temperature Monitoring with ON/OFF (Requires Accurate VIN)
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PART TEMP
RANGE
PIN-
PACKAGE
OUTPUT
VOLTAGE
(V)
MAX5090CATE+ -40°C to +125°C 16 TQFN-EP* Adj
MAX5090CATE -40°C to +125°C 16 TQFN-EP* Adj
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
16 TQFN T1655+3 21-0140 —
PGND
BST
LX
VIN
SGND
FB
VOUT
5V, 2A
Rt Ct
VD
CBST
100µH
3.3µF
COUT
100µF
SS
SYNC
D1
B360
DRAIN
*LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENT AS POSSIBLE.
CSS
CIN
68µF CBYPASS
RIN
VIN
12V
MAX5090B
PTC
ON/OFF
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
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Chip Information
PROCESS: BCD
TRANSISTOR COUNT: 7893
Ordering Information (continued)
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 3/06 Initial release —
1 9/14 No /V OPNs; Removed automotive reference from Applications section 1
Revision History
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX5090A/B/C 2A, 76V, High-Efciency MAXPower
Step-Down DC-DC Converters
© 2014 Maxim Integrated Products, Inc.
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