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19-1448; Rev 0; 3/99
Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin MAX
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 delivered to the power amplifier (PA) via a control voltage. 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-multipleaccess (TDMA) systems, such as GSM, where accurate transmit burst shaping and power control is required. User-selectable current sensing and gain setting resistors maximize flexibility. The MAX4473 operates from a single +2.7V to +6.5V supply 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(R). A low-power shutdown mode reduces supply current to less than 1A and activates an on-board active pull-down at the error amplifier output. Fast enable/disable times of 0.9s reduce average power consumption without compromising dynamic performance. The MAX4473 is available in a space-saving 8-pin MAX package.
Features
o Optimized for GSM Timing Requirements o +2.7V to +6.5V Single-Supply Operation o 1.2mA Supply Current o 1A Supply Current in Shutdown Mode o Guaranteed 1.5s Enable/Disable Times o Active Output Pull-Down in Shutdown Mode o Rail-to-Rail Error Amplifier Output o Rail-to-Rail Power Control Input o Output Drive Capability--500 and 300pF Loads o +1V to VCC Current Sense Input Common-Mode Voltage Range o No Phase-Reversal for Common-Mode Voltage from 0 to VCC o External Current Sensing and Gain Setting Resistors Maximize Flexibility o Available in a Space-Saving 8-pin MAX
MAX4473
Ordering Information
PART MAX4473EUA MAX4473ESA TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 8 MAX 8 SO
Applications
GSM Cellular Phones Cordless Phones Precision Current Control High-Frequency Servo Loops
VCC 0.1F RG1 8 VCC A1 BUFFER 3R V-TO-I CONVERTER A2 Q1 1 SR1 2 SR2 RSENSE
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
RG2
4 PC
A3 ERROR AMPLIFIER
OUT
7 GC IN VCC PA
ICCPA
R 3 SHDN GND 5
MAX4473
SR3 6 RG3 RFIN ICCPA = VPC * RG1 4 * RG3 * RSENSE
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
________________________________________________________________ Maxim Integrated Products 1
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Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin MAX MAX4473
ABSOLUTE MAXIMUM RATINGS
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 = +70C) MAX (derate 4.10mW/C above +70C) .....................330mW SO (derate 5.88mW/C above +70C) ..........................471mW Operating Temperature Range ...........................-40C to +85C Junction Temperature. .....................................................+150C Storage Temperature Range. ............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
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
(VCC = +2.7V to +6.5V, SHDN > +2.4V, MAX4473 test circuit, RG1 = RG2 = 1k 1%, RG3 = 2.5k 1%, RSENSE = 100 1%, RL = 10k, CL = 300pF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +6.0V, VPC = +1.0V, TA = +25C.) (Note 1) PARAMETER GENERAL Supply Voltage Supply Current Shutdown Supply Current SHDN Input High Voltage SHDN Input Low Voltage SHDN Input Current ERROR AMPLIFIER SR1, SR2 Input Offset Voltage SR1, SR2 Input Offset Voltage Drift SR1, SR2 Input Common-Mode Voltage Range SR1, SR2 Input Bias Current SR1, SR2 Input Bias Offset Current SR1, SR2 Shutdown Leakage Current Common-Mode Rejection Ratio Power-Supply Rejection Ratio 1V < VSR1, VSR2 < VCC 1V < VSR1, VSR2 < VCC Inferred from CMRR test; VPC = GND (Note 2) 1V < VSR1, VSR2 < VCC, VPC = GND, SR3 = unconnected 1V < VSR1, VSR2 < VCC, VPC = GND, SR3 = unconnected SHDN < 0.4V, VSR1 = VSR2 = VCC VCC = 2.7V 1V < VSR1, VSR2 < VCC, VPC = GND VCC = 6.5V 2.7V < VCC < 6.5V, VPC = GND VCC = 6.5V, 0.3V < VOUT < 6V RL = 10k to VCC / 2 VCC = 2.7V, 0.3V < VOUT < 2.4V VCC = 6.5V, 0.7V < VOUT < 5.5V RL = 500 to VCC / 2 VCC = 2.7V, 0.7V < VOUT < 2.2V RL = 10k to VCC / 2 RL = 500 to VCC / 2 VOUT = VCC / 2 RL = 10k, CL = 300pF, fo = 10kHz RL = 10k, CL = 300pF Measured from 30% to 70% of VOUT, RL = 10k, CL = 300pF 65 75 80 80 80 80 80 0.15 0.5 1 0.04 0.001 0.001 85 95 90 130 125 130 120 VCC - 0.15 VCC - 0.5 20 2 60 1.8 0.5 10 VCC 1 0.2 0.5 2 mV V/C V A A A dB dB SHDN = 0 to VCC VPC = 0 SHDN < 0.4V, RL = 10k 2.4 0.4 0.5 2.7 1.2 0.03 6.5 2 1 V mA A V V A CONDITIONS MIN TYP MAX UNITS
Large Signal-Gain
dB
Output Voltage Swing Output Current Limit Gain-Bandwidth Product Phase Margin Slew Rate 2
V mA
MHz
degrees
V/s
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Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin MAX
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.7V to +6.5V, SHDN > +2.4V, MAX4473 test circuit, RG1 = RG2 = 1k 1%, RG3 = 2.5k 1%, RSENSE = 100 1%, RL = 10k, CL = 300pF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +6.0V, VPC = +1.0V, TA = +25C.) (Note 1) PARAMETER Capacitive Load Stability Enable/Disable Time PC Input Bias Current SR3 Output Current Limit VPC to VRG1 Ratio PC Input Bandwidth CONDITIONS No sustained oscillations (Note 3) From 50% of SHDN edge to VOUT = 1V, VPC = 2V GND < VPC < VCC - 0.15V VPC = 2.55V, SR1 = SR2 = VCC Measure voltage across RG1, 0.3V < VPC < 2.55V (Note 4) Bandwidth from VPC to VRG1 0.750 0.095 MIN 0 0.9 0.04 4 0.1 2 0.105 TYP MAX 300 1.5 1 UNITS pF s A mA V/V MHz
MAX4473
GAIN CONTROL BUFFER AND V-TO-I CONVERTER
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.
Typical Operating Characteristics
(See Test Circuit, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX4473 toc01
VRG1 / VPC RATIO vs. VPC RESPONSE
VCC = 6.0V 0.1075 0.1050 VRG1 / VPC (V/V) GAIN (dB)
MAX4473 toc02
ERROR-AMPLIFIER RESPONSE
70 60 50 40 30 20 10 0 -10 -20 -30
100k 100 10k 300pF ERROR AMPLIFIER
1.4 TA = -40C 1.2 SUPPLY CURRENT (mA) TA = +25C TA = +85C
0.1100
1.0
0.1025 0.1000 0.0975 0.0950
PHASE
-90 -108 -126 -144 -162 1k 10k 100k 1M -180 10M
0.8
0.6
SHDN = VCC PC = GND 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
0.0925 0.0900 0 1 2 3 VPC (V) 4 5 6
0.4
10
100
SUPPLY VOLTAGE (V)
FREQUENCY
ENABLE/DISABLE TIME
MAX4473 toc04
ERROR-AMPLIFIER OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX4473 toc05
ERROR-AMPLIFIER OUTPUT HIGH VOLTAGE vs. TEMPERATURE
0.40 0.35 VCC - VOH (V) VCC = 6.5V, RL = 500 to VCC / 2
MAX4473 toc06
0.30 0.25 0.20 VOL (V) 0.15 0.10
VCC = 6.5V, RL = 500 to VCC / 2
0.45
SHDN 2V/div VCC = 6.5V VPC = 2V
GND
0.30 0.25 0.20 0.15 VCC = 6.5V, RL = 10k to VCC / 2 VCC = 2.7V, RL = 10k to VCC / 2 -15 10 35 60 85 VCC = 2.7V, RL = 500 to VCC / 2
VCC = 2.7V, RL = 500 to VCC / 2
OUT 500mV/div 500ns/div
GND
0.05 0 -40
VCC = 2.7V, RL = 10k to VCC / 2 VCC = 6.5V, RL = 10k to VCC / 2 -15 10 35 60 85
0.10 0.05 0 -40
TEMPERATURE (C)
TEMPERATURE (C)
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PHASE (degrees)
0 AVCL = 1000 -18 VCC = 6.5V VCM = VCC / 2 -36 VPC = 0 -54 GAIN -72
MAX4473 toc03
3
Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin MAX MAX4473
Pin Description
PIN NAME SR1 SR2 SHDN PC GND SR3 OUT VCC FUNCTION 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. Noninverting Input of Error Amplifier. Connect to load side of current-sense resistor, RSENSE, through gain resistor RG2. Set RG2 equal to RG1. 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 1A. Drive high or connect to VCC for normal operation. Power Control Input. Apply a voltage to PC to set a DC current through the sense resistor to control PA bias. Ground Inverting Input of V-to-I Converter and Source of V-to-I FET, Q1. Connect to ground through gain resistor RG3. Output of Error Amplifier. Connect to gain control pin of power amplifier in bias control applications. +2.7V to +6.5V Voltage Supply Input. Bypass to ground with a 0.1F capacitor.
1
2
3 4 5 6 7 8
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 systems (GSM, DECT), where tight restrictions over the PA's transmit burst and output power require closedloop control over the PA's output power. When used with a PA, the MAX4473 functions as a voltage-controlled 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 controlling 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 railto-rail output error amplifier (A3) (see Typical Operating Circuit). External gain and sense resistors allow programmability for a wide range of applications. In the Typical Operating Circuit, PA supply current flows from the system supply, through the external current 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 supply voltage. Set PA supply current according to the following equation: ICCPA = ( VPC * RG1 ) / ( 4 * RSENSE * RG3 )
Shutdown Mode
When SHDN is a logic-level low (SHDN < 0.4V), amplifiers A1, A2, and A3 are off, Q1 is turned off, and the output of A3 is actively pulled to ground with an Nchannel FET. Supply current is reduced to less than 1A in shutdown mode. Typical power-up time is 0.9s and typical power-down time is 0.3s, using the MAX4473 test circuit.
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 substantially 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 1k and 10k.
4
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Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin MAX
Sense Resistor Selection (RSENSE) Choose RSENSE based on the following criteria: * Voltage Loss: A high R SENSE 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 currents 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.
MAX4473
_________________________Test Circuit
RSENSE VCC 0.1F RG1 1k 1% VCC SR1 100 0.1% RG2 1k 1% SR2 SR1 1 SR2 2 PC SHDN GND
Pin Configuration
TOP VIEW
8 7
VCC OUT SR3 GND
MAX4473
MAX4473
OUT RL 10k RG3 2.5k 1% CL 300pF RE 750 2N3904 SHDN 3 6 5 PC 4
SR3
MAX/SO
Chip Information
TRANSISTOR COUNT: 348
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5
Low-Cost, Low-Voltage, PA Power Control Amplifier for GSM Applications in 8-Pin MAX MAX4473
Package Information
8LUMAXD.EPS
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.
6 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SOICN.EPS

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