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MAX4473EUA+-MAX4473EUA+T
Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications
General DescriptionThe 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.
ApplicationsGSM Cellular Phones
Cordless Phones
Precision Current Control
High-Frequency Servo Loops
FeaturesOptimized for GSM Timing Requirements2.7V to 6.5V Single-Supply Operation1.2mA Supply Current≤1µA Supply Current in Shutdown ModeGuaranteed 1.5µs Enable/Disable TimesActive Output Pull-Down in Shutdown ModeRail-to-Rail Error Amplifier OutputRail-to-Rail Power Control InputOutput Drive Capability—500Ωand 300pF Loads1V to VCCCurrent Sense Input Common-Mode
Voltage RangeNo Phase-Reversal for Common-Mode Voltage
from 0 to VCCExternal Current Sensing and Gain Setting
Resistors Maximize FlexibilityAvailable in a Space-Saving 8-Pin µMAX
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM ApplicationsGND
0.1μF
RFINSHDN
BUFFER6Q1
SR1SR2
SR3
RG3
OUT
V-TO-I
CONVERTERERROR
AMPLIFIER
VCC
VCC
VCC
RSENSE
RG1RG2
ICCPA
MAX4473
4 · RG3 · RSENSE
VPC · RG1ICCPA =
Typical Operating Circuit19-1448; Rev 4; 11/08
Pin Configuration appears at end of data sheet.
Ordering Information
PARTTEMP RANGEPIN-PACKAGEMAX4473EUA-40°C to +85°C8 µMAX
MAX4473ESA-40°C to +85°C8 SO
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
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%,= 10kΩ, CL= 300pF, TA= TMINto 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.
VCCto 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 VCCor 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
PARAMETERCONDITIONSMINTYPMAXUNITS
GENERALSupply Voltage2.76.5V
Supply CurrentVPC = 01.22mA
Shutdown Supply CurrentSHDN < 0.4V, RL = 10Ω0.031µA
SHDN Input High Voltage2.4V
SHDN Input Low Voltage0.4V
SHDN Input CurrentSHDN = 0 to VCC±0.5µA
ERROR AMPLIFIER1V < VSR1, VSR2 < VCC±0.5±2SR1, SR2 Input Offset Voltage1V < VSR1, VSR2 < VCC at +25°C±0.5±1mV
SR1, SR2 Input Offset Voltage
Drift1V < VSR1, VSR2 < VCC10µV/°C
SR1, SR2 Input Common-Mode
Voltage RangeInferred from CMRR test; VSR2 = GND (Note 2)1VCCV
SR1, SR2 Input Bias Current1V < VSR1, VSR2 < VCC, VPC = GND, SR3 = unconnected±0.04±1µA
SR1, SR2 Input Bias Offset
Current1V < VSR1, VSR2 < VCC, VPC = GND, SR3 = unconnected±0.001±0.2µA
SR1, SR2 Shutdown Leakage
CurrentSHDN < 0.4V, VSR1 = VSR2 = VCC±0.001±0.5µA
VCC = 2.7V6585Common-Mode Rejection Ratio1V < VSR1, VSR2 < VCC,
VPC = GNDVCC = 6.5V7595dB
Power-Supply Rejection Ratio2.7V < VCC < 6.5V, VPC = GND8090dB
VCC = 6.5V, 0.3V < VOUT < 6V80130RL = 10kΩ to VCC / 2V C C = 2.7V , 0.3V < V OU T < 2.4V 80125C C = 6.5V , 0.7V < V OU T < 5.5V 80130Large-Signal Gain
RL = 500Ω to VCC / 2V C C = 2.7V , 0.7V < V OU T < 2.2V 80120
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
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%,= 10kΩ, CL= 300pF, TA= TMINto 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.
PARAMETERCONDITIONSMINTYPMAXUNITSRL = 10Ω to VCC / 20.15VCC -
Output Voltage Swing
RL = 500Ω to VCC / 20.5VCC -
Output Current LimitVOUT = VCC / 220mA
Gain-Bandwidth ProductRL = 10Ω, CL = 300pF, fo = 10kHz2MHz
Phase MarginRL = 10Ω, CL = 300pF60degrees
Slew RateMeasured from 30% to 70% of VOUT,
RL = 10Ω, CL = 300pF1.8V/µs
Capacitive-Load StabilityNo sustained oscillations (Note 3)0300pF
Enable/Disable TimeFrom 50% of SHDN edge to VOUT = 1V, VPC = 2V0.91.5µs
GAIN CONTROL BUFFER AND V-TO-I CONVERTERPC Input Bias CurrentGND < VPC < VCC - 0.15V±0.04±1µA
SR3 Output Current LimitVPC < 2.55V, SR1 = SR2 = VCC0.7504mA
VPC to VRG1 RatioMeasure voltage across RG1,
0.3V < VPC < 2.55V (Note 4)0.0950.10.105V/V
PC Input BandwidthBandwidth from VPC to VRG12MHz
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
Typical Operating Characteristics(See Test Circuit, TA= +25°C, unless otherwise noted.)
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
VRG1 / VPC RATIO vs. VPC RESPONSE
MAX4473 toc02
VPC (V)
RG1
/ V
(V/V)
VCC = 6.0V0
-301001k10k100k1M10M
ERROR-AMPLIFIER RESPONSEMAX4473 toc03
FREQUENCY (Hz)
GAIN (dB)
PHASE (degrees)10
PHASEGAIN
AVCL = 1000
VCC = 6.5V
VCM = VCC / 2
VPC = 0
100kΩ
ERROR
AMPLIFIER
100Ω
10kΩ
300pFOUT
500mV/div
SHDN
2V/div
ENABLE/DISABLE TIMEMAX4473 toc04
500ns/div
VCC = 6.5V
VPC = 2V
GND
GND
ERROR-AMPLIFIER
OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX4473 toc05
TEMPERATURE (°C)
(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
ERROR-AMPLIFIER
OUTPUT HIGH VOLTAGE vs. TEMPERATURE
MAX4473 toc06
TEMPERATURE (°C)
CC
(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 DescriptionThe 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 RSENSEequals 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 ModeWhen SHDNis 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
PINNAMEFUNCTIONSR1Inverting 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.SR2Noninverting Input of Error Amplifier. Connect to load side of current-sense resistor, RSENSE, through
gain resistor RG2. Set RG2 equal to RG1.SHDN
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.
4PCPower Control Input. Apply a voltage to PC to set a DC current through the sense resistor to control
PA bias.GNDGroundSR3Inverting Input to V-to-I Converter and Source of V-to-I FET, Q1. Connect to ground through gain
resistor RG3.OUTOutput of Error Amplifier. Connect to gain control pin of power amplifier in bias control applications.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
MAX4473
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
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 RSENSEsub-
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 RSENSEbased on the following criteria:
Voltage Loss:A high RSENSEvalue causes the
power-source voltage to degrade through IR loss.
For minimal voltage loss, use low RSENSEvalues.
Accuracy:A high RSENSEvalue 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
RSENSEto 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 RSENSEare 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 Circuit2N3904
SR1
GND
RSENSE
SR2
OUT
SR3
SHDN
VCC
VCC
300pFRL
10kΩ
RG1
1kΩ
RG2
1kΩ
RG3
2.5kΩ
100Ω
0.1%0.1μF
MAX4473
750Ω
Pin ConfigurationSR3
GNDPC
VCC
OUTSR2
SR1
μMAX/SO
TOP VIEW
MAX4473
SHDN
Chip InformationTRANSISTOR COUNT: 348
