MAXIM MAX8507ETE

19-2918; Rev 1; 1/04
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
Features
The MAX8506/MAX8507/MAX8508 integrate a PWM stepdown 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.
♦ 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)
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 battery 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.
♦ Externally Fixed Output from 0.75V to 3.4V
(MAX8508)
♦ 1MHz Fixed-Frequency PWM Switching
♦ 600mA Guaranteed Output Current
♦ Shutdown Mode 0.1µA (typ)
The MAX8506/MAX8507/MAX8508 are offered in 16-pin
4mm x 4mm thin QFN packages (0.8mm max height).
♦ 16-Pin Thin QFN (4mm x 4mm, 0.8mm max Height)
Applications
Ordering Information
WCDMA/NCDMA Cell Phones
PART
TEMP RANGE
PIN-PACKAGE
Wireless PDAs, Palmtops, and Notebook
Computers
MAX8506ETE
-40°C to +85°C
16 Thin QFN
MAX8507ETE
-40°C to +85°C
16 Thin QFN
Wireless Modems
MAX8508ETE
-40°C to +85°C
16 Thin QFN
Pin Configurations appear at end of data sheet.
cdmaOne is a trademark of CDMA Development Group.
Typical Application Circuits (MAX8506/MAX8507)
INPUT
2.6V TO 5.5V
OUTPUT
0.4V TO 3.4V OR VBATT
4.7µH
4.7µF
2.2µF
BATTP
SKIP
MAX8506
MAX8507
LX
BATT
OUT
0.075Ω
SHDN
REF
REF
PWM
0.4Ω
0.22µF
CURRENTLIMIT
CONTROL
1MHz
OSC
REFIN
DAC
0.3Ω
HP
COMP
PGND
RC*
Cf*
CC*
GND
* RC (kΩ) CC (pF)
MAX8506
1500
10
MAX8507
1000
15
Cf (pF)
100
100
Typical Application Circuits continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX8506/MAX8507/MAX8508
General Description
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
ABSOLUTE MAXIMUM RATINGS
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
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.
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
(V BATT = V BATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, V REFIN = 1.932V (MAX8506), V REFIN = 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
Input BATT Voltage
Undervoltage Lockout Threshold
MIN
TYP
MAX
5.5
V
2.35
2.575
V
2.6
VBATT rising
2.150
Undervoltage Lockout Hysteresis
40
SKIP = GND (normal mode)
180
SKIP = BATT, 1MHz switching
1750
Quiescent Current in Dropout
HP = BATT
775
Shutdown Supply Current
SHDN = GND
Quiescent Current
OUT Voltage Accuracy
OUT Input Resistance
µA
5
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
VREFIN = 0.375V, IOUT = 0 to 30mA (MAX8507)
0.760
0.75
250
485
MAX8507
275
535
-1
0.1
MAX8506
1.76
MAX8507
2.00
1.225
10µA < IREF < 100µA
Reference Bypass Capacitor
V
kΩ
+1
µA
V/V
1.25
1.275
V
2.5
8.5
mV
0.1
0.22
0.7275
0.75
0.7725
V
0.03
0.175
µA
VBATT = 3.6V
0.4
0.825
VBATT = 2.6V
0.5
FB Voltage Accuracy
FB = COMP (MAX8508)
FB Input Current
VFB = 1V (MAX8508)
P-Channel On-Resistance
ILX = 180mA
N-Channel On-Resistance
ILX = 180mA
HP/Bypass P-Channel
On-Resistance
IOUT = 180mA, VBATT = 3.6V
2
µA
0.1
0.740
µA
1000
3.40
Reference Voltage
Reference Load Regulation
250
3.375
REFIN Input Current
REFIN to OUT Gain
mV
VREFIN = 1.932V, IOUT = 0 to 600mA (MAX8506)
MAX8506
UNITS
VBATT = 3.6V
0.3
VBATT = 2.6V
0.35
0.075
_______________________________________________________________________________________
µF
0.5
0.110
Ω
Ω
Ω
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
(V BATT = V BATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, V REFIN = 1.932V (MAX8506), V REFIN = 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
P-Channel Current-Limit
Threshold
MIN
TYP
MAX
UNITS
1.00
1.25
1.50
A
N-Channel Current-Limit
Threshold
SKIP = BATT (PWM mode)
-0.6
-0.45
-0.30
SKIP = GND (normal mode)
0.03
0.05
0.07
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
Minimum Duty Cycle
100
%
SKIP = GND (normal mode)
0
SKIP = BATT
12
COMP Clamp Low Voltage
0.8
COMP Clamp High Voltage
2.0
Transconductance
V
85
150
215
MAX8507
75
130
188
MAX8508
%
V
MAX8506
Current-Sense Transresistance
A
µS
150
260
376
0.36
0.48
0.60
V/A
0.8
1
1.2
MHz
OSCILLATOR
Internal Oscillator Frequency
LOGIC INPUTS (SHDN, HP, SKIP)
Logic-Input High Voltage
VBATT = 2.6V to 5.5V
Logic-Input Low Voltage
VBATT = 2.6V to 5.5V
Logic Input Current
1.6
V
0.1
0.4
V
1
µA
THERMAL SHUTDOWN
Thermal-Shutdown Temperature
Thermal-Shutdown Hysteresis
+160
°C
15
°C
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
MAX8506/MAX8507/MAX8508
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, TA = +25°C, unless otherwise noted.) (See the Typical Application Circuits.)
RLOAD = 15Ω
90
EFFICIENCY vs. INPUT VOLTAGE
100
RLOAD = 15Ω
90
MAX8506 toc03
100
MAX8506 toc01
100
EFFICIENCY vs. OUTPUT VOLTAGE
IN PWM MODE
MAX8506 toc02
EFFICIENCY vs. OUTPUT VOLTAGE
IN NORMAL MODE
90
RLOAD = 10Ω
80
RLOAD = 5Ω
70
EFFICIENCY (%)
EFFICIENCY (%)
RLOAD = 10Ω
80
RLOAD = 5Ω
70
60
0.5
1.0
1.5
2.0
2.5
3.0
60
50
50
3.5
0
0.5
1.5
2.0
2.5
3.0
SKIP = GND
RLOAD = 10Ω
2.5
3.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
EFFICIENCY vs. LOAD CURRENT
DROPOUT VOLTAGE vs. LOAD CURRENT
SUPPLY CURRENT vs. SUPPLY VOLTAGE
IN PWM MODE
VIN = 3.6V
HP = BATT
120
80
VOUT = 1.2V;
PWM
70
VOUT = 2.5V;
PWM
60
90
60
30
VOUT = 1.2V;
NORMAL MODE
50
100
1000
VOUT = 1.2V
3
VOUT = 0.4V
2
0
0
500
LOAD CURRENT (mA)
1000
1500
2000
2.0
LOAD CURRENT (mA)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
IN NORMAL MODE
2.5
3.0
3.5
HEAVY-LOAD SWITCHING WAVEFORM
MAX8506 toc07
SKIP = GND
900
800
VLX
2V/div
VOUT = 3.4V
700
600
500
400
VOUT = 1.2V
300
VOUT
AC-COUPLED
20mV/div
VOUT = 0.4V
200
VOUT = 1.2V
LOAD = 10Ω
100
2.0
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
4.0
4.5
SUPPLY VOLTAGE (V)
MAX8506 toc08
1000
SUPPLY CURRENT (µA)
4
1
0
10
5
SUPPLY CURRENT (mA)
90
6
MAX8506 toc05
150
MAX8506 toc04
VOUT = 2.5V;
NORMAL MODE
4
1.0
VOUT = 0.4V
OUTPUT VOLTAGE (V)
100
1
70
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (mV)
0
VOUT = 1.2V
60
SKIP = GND
50
80
MAX8506 toc06
EFFICIENCY (%)
VOUT = 3.4V
EFFICIENCY (%)
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
5.5
1µs/div
_______________________________________________________________________________________
5.0
5.5
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
LIGHT-LOAD SWITCHING WAVEFORM
IN PWM MODE
LIGHT-LOAD SWITCHING WAVEFORM
IN NORMAL MODE
MAX8506 toc09
MAX8506 toc10
VLX
2V/div
VLX
2V/div
VOUT
AC-COUPLED
5mV/div
VOUT
AC-COUPLED
20mV/div
VOUT = 0.4V
LOAD = 10Ω, SKIP = GND
VOUT = 0.4V
LOAD = 10Ω
1µs/div
400µs/div
EXITING AND ENTERING SHUTDOWN
REFIN TRANSIENT RESPONSE
MAX8506 toc11
MAX8506 toc12
REFIN
1V/div
SHDN
2V/div
0
SKIP = GND
VOUT
1V/div
VOUT
1V/div
SKIP = BATT
0
VREFIN = 0.284V TO 1.420V
VOUT = 1.8V, RLOAD = 10Ω
100µs/div
20µs/div
LINE TRANSIENT RESPONSE
HP TRANSIENT RESPONSE
MAX8506 toc14
MAX8506 toc13
HP
1V/div
VIN
200mV/div
0
3.4V
SKIP = GND
VOUT
1V/div
1.8V
SKIP = BATT
VOUT = 1.8V, RLOAD = 10Ω
20µs/div
VOUT
AC-COUPLED
20mV/div
VOUT = 1.2V, RLOAD = 10Ω
20µs/div
_______________________________________________________________________________________
5
MAX8506/MAX8507/MAX8508
Typical Operating Characteristics (continued)
(VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, TA = +25°C, unless otherwise noted.) (See the Typical Application Circuits.)
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
MAX8506/MAX8507/MAX8508
Pin Description
PIN
NAME
FUNCTION
MAX8506
MAX8507
MAX8508
1
1
SHDN
2
2
GND
Ground. Connect to PGND and directly to EP.
3
3
REF
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.
5
5
COMP
Compensation. Connect a compensation network from COMP to GND to stabilize the
regulator. See the Typical Application Circuits.
6
6
HP
7
7
N.C.
8
8
PGND
Shutdown Control Input. Drive low for shutdown mode. Connect to BATT or logic high to
enable the IC.
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.
No Connection. Connect to PGND.
Power Ground. Connect to GND.
9
9
LX
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
12, 14
12, 14
OUT
Regulator Output. Connect both OUT pins directly to the output voltage.
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.
Supply Voltage Input. Connect all BATT pins to BATTP.
16
16
SKIP
—
4
FB
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.
Detailed Description
The MAX8506/MAX8507/MAX8508 PWM step-down DCDC converters with integrated bypass PFET are optimized 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 settling 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-
6
ponent size. Each device includes an internal synchronous rectifier for high efficiency, which eliminates the
need for an external Schottky diode. The normal operating mode uses constant-frequency PWM switching at
medium and heavy loads and automatically pulse skips
at light loads to reduce supply current and extend battery life. A forced-PWM mode switches at a constant
frequency, regardless of load, to provide a well-controlled spectrum in noise-sensitive applications. Battery
life is maximized by the low-dropout (75mΩ) highpower mode and a 0.1µA (typ) logic-controlled shutdown mode.
_______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
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 associated 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 Pchannel 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 datasampling 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. ForcedPWM 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 oscillator cycle, which permits operation at 100% duty cycle.
Near dropout, cycles can be skipped, reducing switching frequency. However, voltage ripple remains small
because the current ripple is still low. As the input voltage 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 current multiplied by the sum of the internal PMOS onresistance (400mΩ typ) and the inductor resistance.
For lower dropout, use the high-power bypass mode
(75mΩ typ).
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-resistance (75Ω typ) 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.
_______________________________________________________________________________________
7
MAX8506/MAX8507/MAX8508
PWM Control
The MAX8506/MAX8507/MAX8508 use a fixed-frequency, current-mode and PWM controller capable of achieving 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 internal 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-compensation ramp are all summed using a PWM comparator.
The comparator modulates the output power by adjusting 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 capacitor. The resulting load regulation is 0.1% at 0 to 600mA.
MAX8506/MAX8507/MAX8508
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
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 currentcomparator 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 operation, 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 reference, control circuitry, internal switching MOSFET, and
synchronous rectifier turn off and the output becomes
high impedance. Input current falls to 0.1µA (typ) during 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 current-sense comparator used across the P-channel switch
controls entry into skip mode. A third current-sense comparator 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, external components, and internal MOSFETs under overload
conditions.
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 adjusted during operation by driving REFIN with an external
DAC. The MAX8506/MAX8507 output responds to fullscale change in voltage and current in less than 30µs.
Using External Divider (MAX8508)
The MAX8508 is intended for two-step V CC control
applications where high efficiency is a priority. Select
an output voltage between 0.75V and 3.4V by connecting FB to a resistive-divider between the output and
GND (see the MAX8508 Typical Application Circuit).
Select feedback resistor R2 in the 5kΩ to 50kΩ range.
R1 is then given by:
V

R1 = R2 ×  OUT − 1
 VFB

where VFB = 0.75V.
Input Capacitor Selection
Capacitor ESR is a major contributor to input ripple in
high-frequency DC-DC converters. Ordinary aluminumelectrolytic capacitors have high ESR and should be
avoided. Low-ESR tantalum or polymer capacitors are
better and provide a compact solution for space-constrained 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:
Applications Information
Setting the Output Voltage
Using a DAC (MAX8506/MAX8507)
The MAX8506/MAX8507 are optimized for highest system 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 battery current (see the Typical Application Circuits). The
use of DC-DC converters such as the MAX8506/
MAX8507 dramatically extends talk time in these applications.
8
I
IRMS = OUT × VOUT × (VIN − VOUT )
VIN
Compensation, Stability, and
Output Capacitor
The MAX8506/MAX8507/MAX8508 are externally compensated by placing a resistor and a capacitor (see the
Typical Application Circuits, RC and CC) in series from
COMP to GND. An additional capacitor (C f) may be
required from COMP to GND if high-ESR output capacitors are used. The CC capacitor integrates the current
from the transimpedance amplifier, averaging output
_______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
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
D312C
4.7
200
0.790
3.6 x 3.6 x 1.2
SUPPLIER
TOKO
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 gm x RC. Increasing this resistor also increases 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 creates 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 compensation zero must be placed to ensure adequate
phase margin (at least 30° at unity gain). With a 4.7µF
output capacitor, the recommended CC and RC for the
MAX8506 are 1500pF and 10kΩ, respectively. This provides adequate phase margin over the entire output
voltage and load range and optimizes the outputvoltage settling time for REFIN dynamic control. See the
Typical Application Circuits for recommended CC and
RC values for the MAX8507 and MAX8508.
Inductor Selection
A 4µH to 6µH inductor is recommended for most applications. 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
Table 2. Component Suppliers
SUPPLIER
Murata
PHONE
WEBSITE
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
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 filter capacitor as close together as possible and keep their
traces short, direct, and wide. The external voltage- feedback 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 coupling. 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.
_______________________________________________________________________________________
9
MAX8506/MAX8507/MAX8508
Table 1. Suggested Inductors
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
MAX8506/MAX8507/MAX8508
Typical Application Circuits (MAX8508) (continued)
INPUT
2.6V TO 5.5V
OUTPUT
0.75V TO 3.4V OR VBATT
4.7µH
4.7µF
2.2µF
BATTP
LX
BATT
OUT
MAX8508
0.075Ω
SKIP
SHDN
REF
0.4Ω
REF
CURRENTLIMIT
CONTROL
PWM
0.22µF
R1
1MHz
OSC
0.3Ω
FB
R2
HP
0.75V
PGND
COMP
GND
RC
5.6kΩ
CC
2700pF
Cf
100pF
BATT
OUT
BATT
SKIP
BATT
OUT
BATT
TOP VIEW
SKIP
Pin Configurations
16
15
14
13
16
15
14
13
SHDN
1
12
OUT
SHDN
1
12
OUT
GND
2
11
BATT
GND
2
11
BATT
10
BATTP
9
LX
4
7
8
5
6
THIN QFN
4mm x 4mm
7
8
N.C.
3
FB
PGND
REF
HP
LX
COMP
6
BATTP
9
N.C.
5
10
MAX8508
PGND
4
HP
3
COMP
REF
REFIN
MAX8506
MAX8507
THIN QFN
4mm x 4mm
Chip Information
TRANSISTOR COUNT: 2020
PROCESS: BiCMOS
10
______________________________________________________________________________________
PWM Step-Down DC-DC Converters with 75mΩ
Bypass FET for WCDMA and cdmaOne Handsets
24L QFN THIN.EPS
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
B
1
2
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
B
2
2
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.
MAX8506/MAX8507/MAX8508
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.)
This datasheet has been download from:
www.datasheetcatalog.com
Datasheets for electronics components.