General Description
The MAX4473 PA power control IC is intended for
closed-loop bias control of GSM power amplifiers. The
device facilitates accurate control of the current deliv-
ered to the power amplifier (PA) through a control volt-
age. The error amplifier senses the voltage drop across
an external current-sense resistor placed between the
supply and the PA. The output of the error amplifier
adjusts the PA gain until the current is proportional to
the power control voltage applied to the MAX4473. This
unique topology is useful in time-division-multiple-
access (TDMA) systems, such as GSM, where accurate
transmit burst shaping and power control is required.
User-selectable current sensing and gain setting resis-
tors maximize flexibility.
The MAX4473 operates from a single 2.7V to 6.5V sup-
ply and typically draws 1.2mA of supply current. The
error amplifier has a common-mode range that extends
from 1V to VCC. The power control input and error
amplifier outputs swing rail-to-rail. A low-power shut-
down mode reduces supply current to less than 1µA
and activates an on-board active pull-down at the error
amplifier output. Fast enable/disable times of 0.9µs
reduce average power consumption without compro-
mising dynamic performance. The MAX4473 is avail-
able in a space-saving 8-pin µMAX®package.
Applications
GSM Cellular Phones
Cordless Phones
Precision Current Control
High-Frequency Servo Loops
Features
♦Optimized for GSM Timing Requirements
♦2.7V to 6.5V Single-Supply Operation
♦1.2mA Supply Current
♦≤1µA Supply Current in Shutdown Mode
♦Guaranteed 1.5µs Enable/Disable Times
♦Active Output Pull-Down in Shutdown Mode
♦Rail-to-Rail Error Amplifier Output
♦Rail-to-Rail Power Control Input
♦Output Drive Capability—500Ω and 300pF Loads
♦1V to VCC Current Sense Input Common-Mode
Voltage Range
♦No Phase-Reversal for Common-Mode Voltage
from 0 to VCC
♦External Current Sensing and Gain Setting
Resistors Maximize Flexibility
♦Available in a Space-Saving 8-Pin µMAX
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
________________________________________________________________
Maxim Integrated Products
1
GND
PC
0.1μF
8
7
R
3R
A3
PA
GC
IN
RFIN
4
3SHDN
BUFFER
56
A2 Q1
A1
12
SR1 SR2
SR3
RG3
OUT
V-TO-I
CONVERTER ERROR
AMPLIFIER
VCC
VCC
VCC
RSENSE
RG1 RG2
ICCPA
MAX4473
4 · RG3 · RSENSE
VPC · RG1
ICCPA =
Typical Operating Circuit
19-1448; Rev 4; 11/08
Pin Configuration appears at end of data sheet.
Ordering Information
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
MAX4473EUA -40°C to +85°C 8 µMAX
MAX4473ESA -40°C to +85°C 8 SO
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = 2.7V to 6.5V, SHDN > 2.4V, MAX4473 test circuit, RG1 = RG2 = 1kΩ±1%, RG3 = 2.5kΩ±1%, RSENSE = 100Ω±1%,
RL= 10kΩ, CL= 300pF, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 6.0V, VPC = 1.0V, TA= +25°C.) (Note 1)
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.
VCC to GND..............................................................................7V
SR1, SR2, SR3, PC, SHDN,
OUT to GND ............................................-0.3V to (VCC + 0.3V)
SR1 to SR3......................................................................0 to VCC
OUT and SR3 Short-Circuit Duration
to VCC or GND ........................................................Continuous
Current into Any Pin..........................................................±50mA
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate 4.10mW/°C above +70°C) ............330mW
8-Pin SO (derate 5.88mW/°C above +70°C).................471mW
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
PARAMETER CONDITIONS MIN TYP MAX UNITS
GENERAL
Supply Voltage 2.7 6.5 V
Supply Current VPC = 0 1.2 2 mA
Shutdown Supply Current SHDN < 0.4V, RL = 10Ω0.03 1 µA
SHDN Input High Voltage 2.4 V
SHDN Input Low Voltage 0.4 V
SHDN Input Current SHDN = 0 to VCC ±0.5 µA
ERROR AMPLIFIER
1V < VSR1, VSR2 < VCC ±0.5 ±2
SR1, SR2 Input Offset Voltage 1V < VSR1, VSR2 < VCC at +25°C ±0.5 ±1 mV
SR1, SR2 Input Offset Voltage
Drift 1V < VSR1, VSR2 < VCC 10 µV/°C
SR1, SR2 Input Common-Mode
Voltage Range Inferred from CMRR test; VSR2 = GND (Note 2) 1 VCC V
SR1, SR2 Input Bias Current 1V < VSR1, VSR2 < VCC, VPC = GND, SR3 = unconnected ±0.04 ±1 µA
SR1, SR2 Input Bias Offset
Current 1V < VSR1, VSR2 < VCC, VPC = GND, SR3 = unconnected ±0.001 ±0.2 µA
SR1, SR2 Shutdown Leakage
Current SHDN < 0.4V, VSR1 = VSR2 = VCC ±0.001 ±0.5 µA
VCC = 2.7V 65 85
Common-Mode Rejection Ratio 1V < VSR1, VSR2 < VCC,
VPC = GND VCC = 6.5V 75 95 dB
Power-Supply Rejection Ratio 2.7V < VCC < 6.5V, VPC = GND 80 90 dB
VCC = 6.5V, 0.3V < VOUT < 6V 80 130
RL = 10kΩ to VCC / 2 V
C C
= 2.7V , 0.3V < V
OU T
< 2.4V 80 125
V
C C
= 6.5V , 0.7V < V
OU T
< 5.5V 80 130
Large-Signal Gain
RL = 500Ω to VCC / 2 V
C C
= 2.7V , 0.7V < V
OU T
< 2.2V 80 120
dB
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 2.7V to 6.5V, SHDN > 2.4V, MAX4473 test circuit, RG1 = RG2 = 1kΩ±1%, RG3 = 2.5kΩ±1%, RSENSE = 100Ω±1%,
RL= 10kΩ, CL= 300pF, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 6.0V, VPC = 1.0V, TA= +25°C.) (Note 1)
Note 1: Limits over temperature are guaranteed by design.
Note 2: No output phase-reversal for input common-mode voltage range from GND to VCC. Common-mode range limited by voltage
drop across Q1 and RG3.
Note 3: Guaranteed by design.
Note 4: Error dependent on tolerance of RG1, RG2, and RG3. Specified with 0.1% tolerance resistors.
PARAMETER CONDITIONS MIN TYP MAX UNITS
RL = 10Ω to VCC / 2 0.15 VCC -
0.15
Output Voltage Swing
RL = 500Ω to VCC / 2 0.5 VCC -
0.5
V
Output Current Limit VOUT = VCC / 2 20 mA
Gain-Bandwidth Product RL = 10Ω, CL = 300pF, fo = 10kHz 2 MHz
Phase Margin RL = 10Ω, CL = 300pF 60 degrees
Slew Rate Measured from 30% to 70% of VOUT,
RL = 10Ω, CL = 300pF 1.8 V/µs
Capacitive-Load Stability No sustained oscillations (Note 3) 0 300 pF
Enable/Disable Time From 50% of SHDN edge to VOUT = 1V, VPC = 2V 0.9 1.5 µs
GAIN CONTROL BUFFER AND V-TO-I CONVERTER
PC Input Bias Current GND < VPC < VCC - 0.15V ±0.04 ±1 µA
SR3 Output Current Limit VPC < 2.55V, SR1 = SR2 = VCC 0.750 4 mA
VPC to VRG1 Ratio Measure voltage across RG1,
0.3V < VPC < 2.55V (Note 4) 0.095 0.1 0.105 V/V
PC Input Bandwidth Bandwidth from VPC to VRG1 2 MHz
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
4 _______________________________________________________________________________________
Typical Operating Characteristics
(See
Test Circuit
, TA= +25°C, unless otherwise noted.)
0.4
0.6
1.0
0.8
1.2
1.4
2.5 3.5 4.03.0 4.5 5.0 5.5 6.0 6.5
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX4473 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
TA = -40°C
TA = +25°C
TA = +85°C
SHDN = VCC
PC = GND
0.0900
0.0925
0.0950
0.0975
0.1000
0.1025
0.1050
0.1075
0.1100
021 3456
VRG1 / VPC RATIO vs. VPC RESPONSE
MAX4473 toc02
VPC (V)
VRG1 / VPC (V/V)
VCC = 6.0V
70 0
-30
10 100 1k 10k 100k 1M 10M
ERROR-AMPLIFIER RESPONSE
-10
0
-20
MAX4473 toc03
FREQUENCY (Hz)
GAIN (dB)
PHASE (degrees)
10
20
30
40
50
60
-180
-144
-126
-162
-108
-90
-72
-54
-36
-18
PHASE GAIN
AVCL = 1000
VCC = 6.5V
VCM = VCC / 2
VPC = 0
100kΩ
ERROR
AMPLIFIER
100Ω
10kΩ
300pF
OUT
500mV/div
SHDN
2V/div
ENABLE/DISABLE TIME
MAX4473 toc04
500ns/div
VCC = 6.5V
VPC = 2V
GND
GND
0
0.10
0.05
0.20
0.15
0.25
0.30
-40 10-15 35 60 85
ERROR-AMPLIFIER
OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX4473 toc05
TEMPERATURE (°C)
VOL (V)
VCC = 6.5V, RL = 10kΩ to VCC / 2
VCC = 2.7V, RL = 10kΩ to VCC / 2
VCC = 6.5V, RL = 500Ω to VCC / 2
VCC = 2.7V, RL = 500Ω to VCC / 2
0.15
0.10
0.05
0
0.25
0.20
0.35
0.30
0.40
0.45
-40 10-15 35 60 85
ERROR-AMPLIFIER
OUTPUT HIGH VOLTAGE vs. TEMPERATURE
MAX4473 toc06
TEMPERATURE (°C)
VCC - VOH (V)
VCC = 2.7V, RL = 10kΩ to VCC / 2
VCC = 6.5V, RL = 500Ω to VCC / 2
VCC = 6.5V, RL = 10kΩ to VCC / 2
VCC = 2.7V, RL = 500Ω to VCC / 2
MAX4473
Detailed Description
The MAX4473 is a voltage-controlled, unidirectional,
high-side current setting amplifier for applications
where accurate control of PA supply current is desired.
This device is intended for wireless TDMA based sys-
tems (GSM, DECT), where tight restrictions over the
PA’s transmit burst and output power require closed-
loop control over the PA’s output power. When used
with a PA, the MAX4473 functions as a voltage-con-
trolled constant current source, accurately setting PA
supply current by varying the gain of the PA. If you
know the output power versus supply current profile for
the PA, you can set the PA’s output power by control-
ling the amount of supply current delivered to the PA.
The MAX4473 is composed of an input buffer (A1), a
voltage-to-current converting amplifier (A2), and a rail-
to-rail output error amplifier (A3) (see
Typical Operating
Circuit
). External gain and sense resistors allow pro-
grammability for a wide range of applications.
In the
Typical Operating Circuit
, PA supply current
flows from the system supply, through the external cur-
rent-sense resistor (RSENSE), to the PA. The rail-to-rail
outputs of the error amplifier, A3, adjust the gain of the
PA until the voltage drop across RSENSE equals the
voltage drop across external gain resistor, RG1. The
voltage drop across RG1 sets the voltage drop across
RSENSE, with a larger voltage drop resulting in more
current delivered to the PA. The voltage drop across
RG1 is set by A1, A2, and the V-to-I FET, Q1. A voltage
applied to the PC input of the input buffer is divided by
four by a resistor-divider network. A2 forces its inverting
input and the source of Q1 to VPC / 4, thus setting a
voltage across RG3. The resulting current through RG3
sets the current through RG1. This unique architecture
allows the supply current to be set independent of sup-
ply voltage. Set PA supply current according to the fol-
lowing equation:
ICCPA = ( VPC ·RG1 ) / ( 4 ·RSENSE ·RG3 )
Shutdown Mode
When SHDN is a logic-level low (SHDN < 0.4V), ampli-
fiers A1, A2, and A3 are off, Q1 is turned off, and the
output of A3 is actively pulled to ground with an N-
channel FET. Supply current is reduced to less than
1µA in shutdown mode. Typical power-up time is 0.9µs
and typical power-down time is 0.3µs, using the
MAX4473 test circuit.
Pin Description
PIN NAME FUNCTION
1 SR1 Inverting Input of Error Amplifier and Drain of V-to-I FET, Q1. Connect to supply side of current-sense
resistor, RSENSE, through gain resistor RG1.
2 SR2 Noninverting Input of Error Amplifier. Connect to load side of current-sense resistor, RSENSE, through
gain resistor RG2. Set RG2 equal to RG1.
3SHDN
Shutdown Input. Drive SHDN low to disable all amplifiers, pull OUT to GND, set the gate-to-source
voltage of the V-to-I FET (Q1) to 0, and reduce supply current to less than 1µA. Drive high or connect
to VCC for normal operation.
4PC
Power Control Input. Apply a voltage to PC to set a DC current through the sense resistor to control
PA bias.
5 GND Ground
6 SR3 Inverting Input to V-to-I Converter and Source of V-to-I FET, Q1. Connect to ground through gain
resistor RG3.
7 OUT Output of Error Amplifier. Connect to gain control pin of power amplifier in bias control applications.
8 VCC +2.7V to +6.5V Voltage Supply Input. Bypass to ground with a 0.1µF capacitor.
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
_______________________________________________________________________________________ 5
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
6 _______________________________________________________________________________________
Applications Information
Gain Resistor Selection
(RG1, RG2, RG3)
For proper operation, do not make the value of external
gain resistors RG1 and RG2 larger than twice the value
of RG3. In most practical applications, choose RG1
smaller than RG3 to limit the voltage drop over RG1
and RSENSE. A large voltage drop over RSENSE sub-
stantially reduces the voltage applied to the PA, thus
reducing PA output power. Set RG2 equal to RG1 to
compensate for the input bias currents of A3.
Recommended values for RG3 are between 1kΩand
10kΩ.
Sense Resistor Selection (RSENSE)
Choose RSENSE based on the following criteria:
•Voltage Loss: A high RSENSE value causes the
power-source voltage to degrade through IR loss.
For minimal voltage loss, use low RSENSE values.
•Accuracy: A high RSENSE value allows lower cur-
rents to be measured more accurately because input
offset voltages become less significant when the
sense voltage is larger. For best performance, select
RSENSE to provide approximately 100mV of sense
voltage for the full-scale current in each application.
•Efficiency and Power Dissipation: At high current
levels, the I2R losses in RSENSE are significant. Take
this into consideration when choosing the resistor
value and its power dissipation (wattage) rating.
Also, the sense resistor’s value may drift if it is
allowed to heat up excessively.
_________________________Test Circuit
2N3904
SR1
GND
RSENSE
SR2
OUT
SR3
PC
SHDN
VCC
VCC
CL
300pF
RL
10kΩ
RG1
1kΩ
1%
RG2
1kΩ
1%
RG3
2.5kΩ
1%
100Ω
0.1%
0.1μF
MAX4473
RE
750Ω
Pin Configuration
SR3
GNDPC
1
2
8
7
VCC
OUTSR2
SR1
μMAX/SO
TOP VIEW
3
4
6
5
MAX4473
SHDN
Chip Information
TRANSISTOR COUNT: 348
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
_______________________________________________________________________________________ 7
8LUMAXD.EPS
α
α
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
MAX4473
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
8 µMAX U8-1 21-0036
8 SO S8-2 21-0041
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
8 _______________________________________________________________________________________
SOICN .EPS
PACKAGE OUTLINE, .150" SOIC
1
1
21-0041 B
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
MAX
0.010
0.069
0.019
0.157
0.010
INCHES
0.150
0.007
E
C
DIM
0.014
0.004
B
A1
MIN
0.053A
0.19
3.80 4.00
0.25
MILLIMETERS
0.10
0.35
1.35
MIN
0.49
0.25
MAX
1.75
0.050
0.016L0.40 1.27
0.3940.386D
D
MINDIM
D
INCHES
MAX
9.80 10.00
MILLIMETERS
MIN MAX
16 AC
0.337 0.344 AB8.758.55 14
0.189 0.197 AA5.004.80 8
N MS012
N
SIDE VIEW
H 0.2440.228 5.80 6.20
e 0.050 BSC 1.27 BSC
C
HE
eBA1
A
D
0∞-8∞
L
1
VARIATIONS:
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
MAX4473
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
4 11/08 Removed QFN package 1–9
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 _____________________
9
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
