General Description
The MAX8506/MAX8507/MAX8508 integrate a PWM step-
down DC-DC regulator and a 75mΩ(typ) bypass FET to
power the PA in WCDMA and cdmaOne™ cell phones.
The supply voltage range is from 2.6V to 5.5V, and the
guaranteed output current is 600mA. One megahertz
PWM switching allows for small external components.
The MAX8506 and MAX8507 are dynamically controlled
to provide varying output voltages from 0.4V to 3.4V. The
MAX8508 is externally programmed for fixed 0.75V to
3.4V output. Digital logic enables a high-power (HP)
bypass mode that connects the output directly to the bat-
tery for all versions. The MAX8506/MAX8507/MAX8508
are designed so the output settles in less than 30µs for a
full-scale change in output voltage and load current.
The MAX8506/MAX8507/MAX8508 are offered in 16-pin
4mm x 4mm thin QFN packages (0.8mm max height).
Applications
WCDMA/NCDMA Cell Phones
Wireless PDAs, Palmtops, and Notebook
Computers
Wireless Modems
Features
♦Integrated 75mΩ(typ) Bypass FET
♦38mV Dropout at 600mA Load
♦Up to 94% Efficiency
♦Dynamically Adjustable Output from 0.4V to 3.4V
(MAX8506, MAX8507)
♦Externally Fixed Output from 0.75V to 3.4V
(MAX8508)
♦1MHz Fixed-Frequency PWM Switching
♦600mA Guaranteed Output Current
♦Shutdown Mode 0.1µA (typ)
♦16-Pin Thin QFN (4mm x 4mm, 0.8mm max Height)
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2918; Rev 1; 1/04
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
PART TEMP RANGE PIN-PACKAGE
MAX8506ETE -40°C to +85°C 16 Thin QFN
MAX8507ETE -40°C to +85°C 16 Thin QFN
MAX8508ETE -40°C to +85°C 16 Thin QFN
cdmaOne is a trademark of CDMA Development Group. Pin Configurations appear at end of data sheet.
Typical Application Circuits continued at end of data sheet.
CURRENT-
LIMIT
CONTROL
PWM
DAC
BATTP LX OUT
COMP PGND GND
REFIN
1MHz
OSC
REF
HP
INPUT
2.6V TO 5.5V 4.7µH
OUTPUT
0.4V TO 3.4V OR VBATT
4.7µF
0.3Ω
0.4Ω
0.075Ω
BATT
REF
2.2µF
0.22µF
SKIP
SHDN
RC*
CC*
MAX8506
MAX8507
*
10
15
RC (kΩ)
1500
1000
CC (pF)
100
100
Cf (pF)
MAX8506
MAX8507
Cf*
Typical Application Circuits (MAX8506/MAX8507)
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
2_______________________________________________________________________________________
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.
BATTP, BATT, OUT, SHDN, SKIP, HP, REFIN,
FB to GND ...........................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
BATT to BATTP......................................................-0.3V to +0.3V
OUT, COMP, REF to GND.......................-0.3V to (VBATT + 0.3V)
LX Current (Note 1) ...............................................................1.6A
OUT Current (Note 1)............................................................3.2A
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA= +70°C)
16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1.349W
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, VREFIN = 1.932V (MAX8506), VREFIN = 1.70V (MAX8507),
CREF = 0.22µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
Input BATT Voltage 2.6 5.5 V
VBATT rising
2.150 2.35 2.575
V
40 mV
SKIP = GND (normal mode)
180 250
Quiescent Current SKIP = BATT, 1MHz switching
1750
µA
Quiescent Current in Dropout HP = BATT
775 1000
µA
Shutdown Supply Current SHDN = GND 0.1 5 µA
VREFIN = 1.932V, IOUT = 0 to 600mA (MAX8506)
3.375 3.40 3.425
VREFIN = 0.426V, IOUT = 0 to 30mA (MAX8506)
0.740 0.75 0.760
VREFIN = 1.700V, IOUT = 0 to 600mA (MAX8507)
3.375 3.40 3.425
OUT Voltage Accuracy
VREFIN = 0.375V, IOUT = 0 to 30mA (MAX8507)
0.740 0.75 0.760
V
MAX8506
250 485
OUT Input Resistance MAX8507
275 535
kΩ
REFIN Input Current -1 0.1 +1 µA
MAX8506
1.76
REFIN to OUT Gain MAX8507
2.00
V/V
Reference Voltage
1.225 1.25 1.275
V
Reference Load Regulation 10µA < IREF < 100µA 2.5 8.5 mV
Reference Bypass Capacitor 0.1
0.22
µF
FB Voltage Accuracy FB = COMP (MAX8508)
0.7275 0.75 0.7725
V
FB Input Current VFB = 1V (MAX8508)
0.03 0.175
µA
VBATT = 3.6V 0.4
0.825
P-Channel On-Resistance ILX = 180mA VBATT = 2.6V 0.5 Ω
VBATT = 3.6V 0.3 0.5
N-Channel On-Resistance ILX = 180mA VBATT = 2.6V
0.35
Ω
HP/Bypass P-Channel
On-Resistance IOUT = 180mA, VBATT = 3.6V
0.075 0.110
Ω
Note 1: LX has internal clamp diodes to PGND and BATT. Applications that forward bias these diodes should take care not to exceed
the IC’s package power-dissipation limits.
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
_______________________________________________________________________________________ 3
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
P-Channel Current-Limit
Threshold
1.00 1.25 1.50
A
SKIP = BATT (PWM mode)
-0.6 -0.45 -0.30
N-Channel Current-Limit
Threshold SKIP = GND (normal mode)
0.03 0.05 0.07
A
P-Channel Pulse-Skipping
Current Threshold SKIP = GND (normal mode)
0.050 0.125 0.170
A
HP/Bypass P-Channel
Current-Limit Threshold VOUT = 3.1V 0.8 1.5 2.5 A
LX Leakage Current -2
0.01
+2 µA
OUT Leakage Current -2
0.01
+2 µA
Maximum Duty Cycle
100
%
SKIP = GND (normal mode) 0
Minimum Duty Cycle SKIP = BATT 12 %
COMP Clamp Low Voltage 0.8 V
COMP Clamp High Voltage 2.0 V
MAX8506 85
150 215
MAX8507 75
130 188
Transconductance
MAX8508
150 260 376
µS
Current-Sense Transresistance
0.36 0.48 0.60
V/A
OSCILLATOR
Internal Oscillator Frequency 0.8 1 1.2
MHz
LOGIC INPUTS (SHDN, HP, SKIP)
Logic-Input High Voltage VBATT = 2.6V to 5.5V 1.6 V
Logic-Input Low Voltage VBATT = 2.6V to 5.5V 0.4 V
Logic Input Current 0.1 1 µA
THERMAL SHUTDOWN
Thermal-Shutdown Temperature
+160
°C
Thermal-Shutdown Hysteresis 15 °C
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, VREFIN = 1.932V (MAX8506), VREFIN = 1.70V (MAX8507),
CREF = 0.22µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
4_______________________________________________________________________________________
Typical Operating Characteristics
(VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, TA= +25°C, unless otherwise noted.) (See the Typical Application Circuits.)
EFFICIENCY vs. OUTPUT VOLTAGE
IN NORMAL MODE
MAX8506 toc01
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
3.02.52.01.51.00.5
60
70
80
90
100
50
0 3.5
RLOAD = 15Ω
RLOAD = 10Ω
RLOAD = 5Ω
SKIP = GND
EFFICIENCY vs. OUTPUT VOLTAGE
IN PWM MODE
MAX8506 toc02
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
3.02.52.01.51.00.5
60
70
80
90
100
50
0 3.5
RLOAD = 15Ω
RLOAD = 10Ω
RLOAD = 5Ω
EFFICIENCY vs. INPUT VOLTAGE
5.04.54.03.53.02.5 5.5
MAX8506 toc03
INPUT VOLTAGE (V)
EFFICIENCY (%)
60
70
80
90
100
50
VOUT = 0.4V
VOUT = 1.2V
VOUT = 3.4V
SKIP = GND
RLOAD = 10Ω
LOAD CURRENT (mA)
100101 1000
EFFICIENCY vs. LOAD CURRENT
MAX8506 toc04
EFFICIENCY (%)
60
70
80
90
100
50
VOUT = 2.5V;
NORMAL MODE
VOUT = 2.5V;
PWM
VOUT = 1.2V;
NORMAL MODE
VOUT = 1.2V;
PWM
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX8506 toc05
LOAD CURRENT (mA)
OUTPUT VOLTAGE (mV)
15001000500
30
60
90
120
150
0
0 2000
VIN = 3.6V
HP = BATT
SUPPLY CURRENT vs. SUPPLY VOLTAGE
IN PWM MODE
MAX8506 toc06
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.04.54.03.53.02.5
1
2
3
4
5
6
0
2.0 5.5
VOUT = 1.2V
VOUT = 0.4V
200
300
400
500
600
700
800
900
1000
100
SUPPLY CURRENT vs. SUPPLY VOLTAGE
IN NORMAL MODE
MAX8506 toc07
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
5.04.54.03.53.02.52.0 5.5
VOUT = 1.2V
VOUT = 3.4V
VOUT = 0.4V
SKIP = GND
HEAVY-LOAD SWITCHING WAVEFORM
MAX8506 toc08
1µs/div
VLX
2V/div
VOUT
AC-COUPLED
20mV/div
VOUT = 1.2V
LOAD = 10Ω
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
_______________________________________________________________________________________ 5
MAX8506 toc09
400µs/div
VLX
2V/div
VOUT
AC-COUPLED
5mV/div
LIGHT-LOAD SWITCHING WAVEFORM
IN PWM MODE
VOUT = 0.4V
LOAD = 10Ω
LIGHT-LOAD SWITCHING WAVEFORM
IN NORMAL MODE
MAX8506 toc10
1µs/div
VLX
2V/div
VOUT
AC-COUPLED
20mV/div
VOUT = 0.4V
LOAD = 10Ω, SKIP = GND
EXITING AND ENTERING SHUTDOWN
MAX8506 toc11
100µs/div
VOUT
1V/div
SHDN
2V/div
VOUT = 1.8V, RLOAD = 10Ω
REFIN TRANSIENT RESPONSE
MAX8506 toc12
20µs/div
VOUT
1V/div
0
0
REFIN
1V/div
SKIP = GND
SKIP = BATT
VREFIN = 0.284V TO 1.420V
HP TRANSIENT RESPONSE
MAX8506 toc13
20µs/div
VOUT
1V/div
1.8V
0
HP
1V/div
SKIP = GND
SKIP = BATT
VOUT = 1.8V, RLOAD = 10Ω
LINE TRANSIENT RESPONSE
MAX8506 toc14
20µs/div
VIN
200mV/div
3.4V
VOUT
AC-COUPLED
20mV/div
VOUT = 1.2V, RLOAD = 10Ω
Typical Operating Characteristics (continued)
(VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, TA= +25°C, unless otherwise noted.) (See the Typical Application Circuits.)
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
6_______________________________________________________________________________________
Detailed Description
The MAX8506/MAX8507/MAX8508 PWM step-down DC-
DC converters with integrated bypass PFET are opti-
mized for low-voltage, battery-powered applications
where high efficiency and small size are priorities. An
analog control signal dynamically adjusts the MAX8506/
MAX8507s’ output voltage from 0.4V to 3.4V with a set-
tling time of 30µs. The MAX8508 uses external feedback
resistors to set the output voltage from 0.75V to 3.4V.
The MAX8506/MAX8507/MAX8508 operate at a high
1MHz switching frequency that reduces external com-
ponent size. Each device includes an internal synchro-
nous rectifier for high efficiency, which eliminates the
need for an external Schottky diode. The normal operat-
ing mode uses constant-frequency PWM switching at
medium and heavy loads and automatically pulse skips
at light loads to reduce supply current and extend bat-
tery life. A forced-PWM mode switches at a constant
frequency, regardless of load, to provide a well-con-
trolled spectrum in noise-sensitive applications. Battery
life is maximized by the low-dropout (75mΩ) high-
power mode and a 0.1µA (typ) logic-controlled shut-
down mode.
Pin Description
PIN
MAX8506
MAX8507
MAX8508
NAME
FUNCTION
11SHDN Shutdown Control Input. Drive low for shutdown mode. Connect to BATT or logic high to
enable the IC.
22GND Ground. Connect to PGND and directly to EP.
33REF Reference Output. Output of the internal 1.25V reference. Bypass to GND with a 0.22µF
capacitor.
4—REFIN External Reference Input. Connect to the output of a digital-to-analog converter for
dynamic adjustment of the output voltage.
55
COMP
Compensation. Connect a compensation network from COMP to GND to stabilize the
regulator. See the Typical Application Circuits.
66HP
High-Power Bypass Control Input. Drive low for OUT to regulate to the voltage set by
REFIN (MAX8506/MAX8507) or the external resistors on FB (MAX8508). Drive HP high for
OUT to be connected to BATT by an internal bypass PFET.
77N.C. No Connection. Connect to PGND.
88PGND Power Ground. Connect to GND.
99LX
Inductor Connection to the Drains of the Internal Power MOSFETs. LX is high impedance
in shutdown mode.
10 10
BATTP
Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass BATTP to PGND with a
low-ESR 2.2µF capacitor. Connect BATTP to BATT.
11, 13, 15
11, 13, 15
BATT Supply Voltage Input. Connect all BATT pins to BATTP.
12, 14 12, 14 OUT Regulator Output. Connect both OUT pins directly to the output voltage.
16 16 SKIP Skip Control Input. Connect to GND or drive low to enable pulse skipping under light
loads. Connect SKIP to BATT or logic high for forced-PWM mode.
—4FB
Output Feedback Sense Input. To set the output voltage, connect FB to the center of an
external resistive voltage-divider between OUT and GND. FB voltage regulates to 0.75V
when HP is low.
——EP Exposed Pad. Connect directly to GND underneath the IC.
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
_______________________________________________________________________________________ 7
PWM Control
The MAX8506/MAX8507/MAX8508 use a fixed-frequen-
cy, current-mode and PWM controller capable of achiev-
ing 100% duty cycle. Current-mode feedback provides
cycle-by-cycle current limiting and superior load and line
response, as well as overcurrent protection for the inter-
nal MOSFET and rectifier. A comparator at the P-channel
MOSFET switch detects overcurrent at 1.25A.
During PWM operation, the MAX8506/MAX8507/
MAX8508 regulate the output voltage by switching at a
constant frequency and then modulating the duty cycle
with PWM control. The error-amp output, the main
switch current-sense signal, and the slope-compensa-
tion ramp are all summed using a PWM comparator.
The comparator modulates the output power by adjust-
ing the peak inductor current during the first half of
each cycle based on the output-error voltage. The
MAX8506/MAX8507/MAX8508 have relatively low AC
loop gain coupled with a high-gain integrator to enable
the use of a small and low-valued output filter capaci-
tor. The resulting load regulation is 0.1% at 0 to 600mA.
Normal-Mode Operation
Connecting SKIP to GND enables normal operation. This
allows automatic PWM control at medium and heavy
loads and skip mode at light loads to improve efficiency
and reduce quiescent current to 180µA. Operating in
normal mode allows the MAX8506/MAX8507/MAX8508
to pulse skip when the peak inductor current drops
below 90mA. During skip operation, the MAX8506/
MAX8507/MAX8508 switch only as needed to service
the load, reducing the switching frequency and associat-
ed losses in the internal switch and synchronous rectifier.
There are three steady-state operating conditions for
the MAX8506/MAX8507/MAX8508 in normal mode:
1) The device performs in continuous conduction for
heavy loads in a manner identical to forced-PWM
mode. 2) The inductor current becomes discontinuous
at medium loads, requiring the synchronous rectifier to
be turned off before the end of a cycle as the inductor
current reaches zero. 3) The device enters into skip
mode when the converter output voltage exceeds its
regulation limit before the inductor current reaches its
skip threshold level.
During skip mode, a switching cycle initiates when the
output voltage has dropped out of regulation. The P-
channel MOSFET switch turns on and conducts current
to the output-filter capacitor and load until the inductor
current reaches the pulse-skipping current threshold.
Then the main switch turns off and the magnetic field in
the inductor collapses while current flows through the
synchronous rectifier to the output filter capacitor and
the load. The synchronous rectifier is turned off when
the inductor current reaches zero. The MAX8506/
MAX8507/MAX8508 wait until the skip comparator
senses a low output voltage again.
Forced-PWM Operation
Connect SKIP to BATT for forced-PWM operation.
Forced-PWM operation is desirable in sensitive RF and
data-acquisition applications to ensure that switching
harmonics do not interfere with sensitive IF and data-
sampling frequencies. A minimum load is not required
during forced-PWM operation since the synchronous
rectifier passes reverse-inductor current as needed to
allow constant-frequency operation with no load. Forced-
PWM operation uses higher supply current with no load
(1.75mA typ) compared to skip mode (180µA typ).
100% Duty-Cycle Operation and Dropout
The maximum on-time can exceed one internal oscilla-
tor cycle, which permits operation at 100% duty cycle.
Near dropout, cycles can be skipped, reducing switch-
ing frequency. However, voltage ripple remains small
because the current ripple is still low. As the input volt-
age drops even further, the duty cycle increases until
the internal P-channel MOSFET stays on continuously.
Dropout voltage at 100% duty cycle is the output cur-
rent multiplied by the sum of the internal PMOS on-
resistance (400mΩtyp) and the inductor resistance.
For lower dropout, use the high-power bypass mode
(75mΩtyp).
High-Power Bypass Mode
A high-power bypass mode is available for use when a
PA transmits at high power. This mode connects OUT
to BATT through the bypass PFET. Additionally, the
PWM buck converter is forced into 100% duty cycle to
further reduce dropout. The dropout in the bypass
PFET equals the load current multiplied by the on-resis-
tance (75Ωtyp) in parallel with the buck converter and
inductor dropout resistance.
Undervoltage Lockout (UVLO)
The MAX8506/MAX8507/MAX8508 do not operate with
battery voltages below the UVLO threshold of 2.35V
(typ). The output remains off until the supply voltage
exceeds the UVLO threshold. This guarantees the
integrity of the output voltage regulation.
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
8_______________________________________________________________________________________
Synchronous Rectification
An N-channel synchronous rectifier operates during the
second half of each switching cycle (off-time). When
the inductor current falls below the N-channel current-
comparator threshold or when the PWM reaches the
end of the oscillator period, the synchronous rectifier
turns off. This prevents reverse current from the output
to the input in pulse-skipping mode. During PWM oper-
ation, the NEGLIM threshold adjusts to permit reverse
current during light loads. This allows regulation with a
constant switching frequency and eliminates minimum
load requirements for fixed-frequency operation.
Shutdown Mode
Drive SHDN to GND to place the MAX8506/MAX8507/
MAX8508 in shutdown mode. In shutdown, the refer-
ence, control circuitry, internal switching MOSFET, and
synchronous rectifier turn off and the output becomes
high impedance. Input current falls to 0.1µA (typ) dur-
ing shutdown mode. Drive SHDN high to enable the IC.
Current-Sense Comparators
The MAX8506/MAX8507/MAX8508 use several internal
current-sense comparators. In PWM operation, the PWM
comparator terminates the cycle-by-cycle on-time and
provides improved load and line response. A second cur-
rent-sense comparator used across the P-channel switch
controls entry into skip mode. A third current-sense com-
parator monitors current through the internal N-channel
MOSFET to prevent excessive reverse currents and
determine when to turn off the synchronous rectifier. A
fourth comparator used at the P-channel MOSFET
detects overcurrent. A fifth comparator used at the
bypass P-channel MOSFET detects overcurrent in the
HP mode or at dropout. This protects the system, exter-
nal components, and internal MOSFETs under overload
conditions.
Applications Information
Setting the Output Voltage
Using a DAC (MAX8506/MAX8507)
The MAX8506/MAX8507 are optimized for highest sys-
tem efficiency when applying power to a linear PA in
CDMA handsets. When transmitting at less than full
power, the supply voltage to the PA is lowered in many
steps from 3.4V to as low as 0.4V to greatly reduce bat-
tery current (see the Typical Application Circuits). The
use of DC-DC converters such as the MAX8506/
MAX8507 dramatically extends talk time in these appli-
cations.
The MAX8506/MAX8507s’ output voltage is dynamically
adjustable from 0.4V to 3.4V by the use of the REFIN
input. The gain from VREFIN to VOUT is internally set to
1.76 (MAX8506) or 2.00 (MAX8507). VOUT can be adjust-
ed during operation by driving REFIN with an external
DAC. The MAX8506/MAX8507 output responds to full-
scale change in voltage and current in less than 30µs.
Using External Divider (MAX8508)
The MAX8508 is intended for two-step VCC control
applications where high efficiency is a priority. Select
an output voltage between 0.75V and 3.4V by connect-
ing FB to a resistive-divider between the output and
GND (see the MAX8508 Typical Application Circuit).
Select feedback resistor R2 in the 5kΩto 50kΩrange.
R1 is then given by:
where VFB = 0.75V.
Input Capacitor Selection
Capacitor ESR is a major contributor to input ripple in
high-frequency DC-DC converters. Ordinary aluminum-
electrolytic capacitors have high ESR and should be
avoided. Low-ESR tantalum or polymer capacitors are
better and provide a compact solution for space-con-
strained surface-mount designs. Ceramic capacitors
have the lowest overall ESR.
The input filter capacitor reduces peak currents and
noise at the input voltage source. Connect a low-ESR
bulk capacitor (2.2µF to 10µF) to the input. Select this
bulk capacitor to meet the input ripple requirements
and voltage rating rather than capacitance value. Use
the following equation to calculate the maximum RMS
input current:
Compensation, Stability, and
Output Capacitor
The MAX8506/MAX8507/MAX8508 are externally com-
pensated by placing a resistor and a capacitor (see the
Typical Application Circuits, RCand CC) in series from
COMP to GND. An additional capacitor (Cf) may be
required from COMP to GND if high-ESR output capaci-
tors are used. The CCcapacitor integrates the current
from the transimpedance amplifier, averaging output
II
VVVV
RMS OUT
IN OUT IN OUT
=× ×−()
RR V
V
OUT
FB
12 1=× −
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
_______________________________________________________________________________________ 9
capacitor ripple. This sets the device speed for transient
response and allows the use of small ceramic output
capacitors because the phase-shifted capacitor ripple
does not disturb the current-regulation loop. The resistor
sets the proportional gain of the output error voltage by
a factor of gmx RC. Increasing this resistor also increas-
es the sensitivity of the control loop to output ripple.
The resistor and capacitor set a compensation zero that
defines the system’s transient response. The load cre-
ates a dynamic pole, shifting in frequency with changes
in load. As the load decreases, the pole frequency
shifts to the left. System stability requires that the com-
pensation zero must be placed to ensure adequate
phase margin (at least 30° at unity gain). With a 4.7µF
output capacitor, the recommended CCand RCfor the
MAX8506 are 1500pF and 10kΩ, respectively. This pro-
vides adequate phase margin over the entire output
voltage and load range and optimizes the output-
voltage settling time for REFIN dynamic control. See the
Typical Application Circuits for recommended CCand
RCvalues for the MAX8507 and MAX8508.
Inductor Selection
A 4µH to 6µH inductor is recommended for most appli-
cations. For best efficiency, the inductor’s DC resistance
should be <400mΩ. Saturation current (ISAT) should be
greater than the maximum DC load at the PA’s supply
plus half the inductor current ripple. Two-step VCC
applications typically require very small inductors with
ISAT in the 200mA to 300mA region. See Tables 1 and 2
for recommended inductors and suppliers.
PC Board Layout and Routing
High switching frequencies and large peak currents
make PC board layout a very important part of design.
Good design minimizes EMI, noise on the feedback
paths, and voltage gradients in the ground plane, all of
which can result in instability or regulation errors.
Connect the inductor, input filter capacitor, and output fil-
ter capacitor as close together as possible and keep their
traces short, direct, and wide. The external voltage- feed-
back network should be very close to the FB pin, within
0.2in (5mm). Keep noisy traces, such as those from the
LX pin, away from the voltage-feedback network. Position
the bypass capacitors as close as possible to their
respective supply and ground pins to minimize noise cou-
pling. For optimum performance, place input and output
capacitors as close to the device as possible. Connect
GND directly under the IC to the exposed paddle. Refer
to the MAX8506 evaluation kit for an example PC board
layout and routing scheme.
SUPPLIER PHONE WEBSITE
Murata 770-436-1300
www.murata.com
Sumida 847-956-0666
www.sumida.com
Taiyo Yuden 408-573-4150
www.t-yuden.com
TOKO 847-297-0070
www.tokoam.com
Table 2. Component Suppliers
Table 1. Suggested Inductors
SUPPLIER PART
NUMBER
INDUCTANCE
(µH) ESR (mΩ)SATURATION
CURRENT (A)
DIMENSIONS (mm)
Murata LQH32C-53 4.7 150 0.650 2.5 x 3.2 x 1.7
Sumida CDRH2D11 4.7 135 0.500 3.2 x 3.2 x 1.2
Taiyo Yuden LBLQ2016 4.7 250 0.210 1.6 x 2.0 x 1.6
TOKO D312C 4.7 200 0.790 3.6 x 3.6 x 1.2
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
10 ______________________________________________________________________________________
16 15 14 13
BATT
OUT
BATT
9
10
11
12
LX
BATTP
BATT
OUT
4
3
2
1
FB
REF
GND
5678
COMP
HP
N.C.
PGND
SHDN
SKIP
THIN QFN
4mm x 4mm
16 15 14 13
BATT
OUT
BATT
9
10
11
12
LX
BATTP
BATT
OUT
4
3
2
1
REFIN
REF
GND
5678
COMP
HP
N.C.
PGND
SHDN
SKIP
THIN QFN
4mm x 4mm
TOP VIEW
MAX8508
MAX8506
MAX8507
Pin Configurations
CURRENT-
LIMIT
CONTROL
PWM
BATTP LX
OUT
FB
COMP PGND GND
1MHz
OSC
REF
HP
INPUT
2.6V TO 5.5V 4.7µH
OUTPUT
0.75V TO 3.4V OR VBATT
4.7µF
0.3Ω
0.4Ω
0.075Ω
BATT
REF
2.2µF
0.22µF
SKIP
SHDN
RC
5.6kΩ
CC
2700pF
Cf
100pF
MAX8508
0.75V
R1
R2
Typical Application Circuits (MAX8508) (continued)
Chip Information
TRANSISTOR COUNT: 2020
PROCESS: BiCMOS
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75m
ΩΩ
Bypass FET for WCDMA and cdmaOne Handsets
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11
©2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
C1
2
21-0139
PACKAGE OUTLINE
12, 16, 20, 24L THIN QFN, 4x4x0.8mm
C
2
2
21-0139
PACKAGE OUTLINE
12, 16, 20, 24L THIN QFN, 4x4x0.8mm