19-1448; Rev 4; 11/08
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
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 V
CC
. 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.
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 V
CC
Current Sense Input Common-Mode
Voltage Range
♦
No Phase-Reversal for Common-Mode Voltage
from 0 to V
CC
♦
External Current Sensing and Gain Setting
Resistors Maximize Flexibility
♦
Available in a Space-Saving 8-Pin
µMAX
MAX4473
Ordering Information
PART
MAX4473EUA
MAX4473ESA
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 µMAX
8 SO
Applications
GSM Cellular Phones
Cordless Phones
Precision Current Control
High-Frequency Servo Loops
µMAX is a registered trademark of Maxim Integrated Products, Inc.
V
CC
0.1μF
RG1
8
V
CC
A1
BUFFER
3R
V-TO-I
CONVERTER
A2
Q1
1
SR1
2
SR2
A3
R
SENSE
RG2
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
4 PC
OUT
7
GC
IN V
CC
PA
I
CCPA
ERROR
AMPLIFIER
R
3 SHDN
GND
5
MAX4473
SR3
6
RG3
RFIN
I
CCPA
=
V
PC
·
RG1
4
·
RG3
·
R
SENSE
________________________________________________________________
Maxim Integrated Products
1
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.
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
MAX4473
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND..............................................................................7V
SR1, SR2, SR3, PC,
SHDN,
OUT to GND ............................................-0.3V to (V
CC
+ 0.3V)
SR1 to SR3......................................................................0 to V
CC
OUT and SR3 Short-Circuit Duration
to V
CC
or GND ........................................................Continuous
Current into Any Pin..........................................................±50mA
Continuous Power Dissipation (T
A
= +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
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
CC
= 2.7V to 6.5V,
SHDN
> 2.4V, MAX4473 test circuit, RG1 = RG2 = 1kΩ ±1%, RG3 = 2.5kΩ ±1%, R
SENSE
= 100Ω ±1%,
R
L
= 10kΩ, C
L
= 300pF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at V
CC
= 6.0V, V
PC
= 1.0V, T
A
= +25°C.) (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
SHDN
= 0 to V
CC
1V < V
SR1
, V
SR2
< V
CC
1V < V
SR1
, V
SR2
< V
CC
at +25°C
1V < V
SR1
, V
SR2
< V
CC
Inferred from CMRR test; V
SR2
= GND (Note 2)
1V < V
SR1
, V
SR2
< V
CC
, V
PC
= GND, SR3 = unconnected
1V < V
SR1
, V
SR2
< V
CC
, V
PC
= GND, SR3 = unconnected
SHDN
< 0.4V, V
SR1
= V
SR2
= V
CC
1V < V
SR1
, V
SR2
< V
CC
, V
CC
= 2.7V
V
PC
= GND
V
CC
= 6.5V
2.7V < V
CC
< 6.5V, V
PC
= GND
R
L
= 10kΩ to V
CC
/ 2
Large-Signal Gain
R
L
= 500Ω to V
CC
/ 2
V
CC
= 6.5V, 0.3V < V
OUT
< 6V
V
CC
= 2.7V, 0.3V < V
OUT
< 2.4V
V
CC
= 6.5V, 0.7V < V
OUT
< 5.5V
V
CC
= 2.7V, 0.7V < V
OUT
< 2.2V
65
75
80
80
80
80
80
1
±0.04
±0.001
±0.001
85
95
90
130
125
130
120
dB
±0.5
±0.5
10
V
CC
±1
±0.2
±0.5
V
PC
= 0
SHDN
< 0.4V, R
L
= 10Ω
2.4
0.4
±0.5
±2
±1
2.7
1.2
0.03
6.5
2
1
V
mA
µA
V
V
µA
CONDITIONS
MIN
TYP
MAX
UNITS
mV
µV/°C
V
µA
µA
µA
dB
dB
2
_______________________________________________________________________________________
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
MAX4473
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 2.7V to 6.5V,
SHDN
> 2.4V, MAX4473 test circuit, RG1 = RG2 = 1kΩ ±1%, RG3 = 2.5kΩ ±1%, R
SENSE
= 100Ω ±1%,
R
L
= 10kΩ, C
L
= 300pF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at V
CC
= 6.0V, V
PC
= 1.0V, T
A
= +25°C.) (Note 1)
PARAMETER
R
L
= 10Ω to V
CC
/ 2
Output Voltage Swing
R
L
= 500Ω to V
CC
/ 2
Output Current Limit
Gain-Bandwidth Product
Phase Margin
Slew Rate
Capacitive-Load Stability
Enable/Disable Time
PC Input Bias Current
SR3 Output Current Limit
V
PC
to VRG1 Ratio
PC Input Bandwidth
V
OUT
= V
CC
/ 2
R
L
= 10Ω, C
L
= 300pF, f
o
= 10kHz
R
L
= 10Ω, C
L
= 300pF
Measured from 30% to 70% of V
OUT
,
R
L
= 10Ω, C
L
= 300pF
No sustained oscillations (Note 3)
From 50% of
SHDN
edge to V
OUT
= 1V, V
PC
= 2V
GND < V
PC
< V
CC
- 0.15V
V
PC
< 2.55V, SR1 = SR2 = V
CC
Measure voltage across RG1,
0.3V < V
PC
< 2.55V (Note 4)
Bandwidth from V
PC
to V
RG1
0.750
0.095
0
0.9
±0.04
4
0.1
2
0.105
0.5
20
2
60
1.8
300
1.5
±1
V
CC
-
0.5
mA
MHz
degrees
V/µs
pF
µs
µA
mA
V/V
MHz
CONDITIONS
MIN
0.15
TYP
MAX
V
CC
-
0.15
V
UNITS
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 V
CC
. 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.
_______________________________________________________________________________________
3
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
MAX4473
Typical Operating Characteristics
(See
Test Circuit,
T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX4473 toc01
V
RG1
/ V
PC
RATIO vs. V
PC
RESPONSE
V
CC
= 6.0V
0.1075
0.1050
V
RG1
/ V
PC
(V/V)
MAX4473 toc02
1.4
T
A
= -40°C
1.2
SUPPLY CURRENT (mA)
T
A
= +25°C
T
A
= +85°C
0.1100
1.0
0.1025
0.1000
0.0975
0.0950
0.8
0.6
SHDN = V
CC
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
V
PC
(V)
4
5
6
0.4
SUPPLY VOLTAGE (V)
ERROR-AMPLIFIER RESPONSE
70
60
50
40
GAIN (dB)
30
20
10
0
-10
-20
-30
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
100kΩ
100Ω
10kΩ
300pF
MAX4473 toc03
ENABLE/DISABLE TIME
MAX4473 toc04
PHASE
-90
ERROR
AMPLIFIER
-108
-126
-144
-162
-180
10M
PHASE (degrees)
A
VCL
= 1000
-18
V
CC
= 6.5V
V
CM
= V
CC
/ 2
-36
V
PC
= 0
-54
GAIN
-72
0
SHDN
2V/div
V
CC
= 6.5V
V
PC
= 2V
GND
OUT
500mV/div
500ns/div
GND
ERROR-AMPLIFIER
OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX4473 toc05
ERROR-AMPLIFIER
OUTPUT HIGH VOLTAGE vs. TEMPERATURE
0.40
0.35
V
CC
- V
OH
(V)
V
CC
= 6.5V, R
L
= 500Ω to V
CC
/ 2
MAX4473 toc06
0.30
0.25
0.20
V
OL
(V)
0.15
0.10
0.05
V
CC
= 6.5V, R
L
= 500Ω to V
CC
/ 2
0.45
0.30
0.25
0.20
0.15
V
CC
= 6.5V, R
L
= 10kΩ to V
CC
/ 2
V
CC
= 2.7V, R
L
= 10kΩ to V
CC
/ 2
-15
10
35
60
85
V
CC
= 2.7V, R
L
= 500Ω to V
CC
/ 2
V
CC
= 2.7V, R
L
= 500Ω to V
CC
/ 2
V
CC
= 2.7V, R
L
= 10kΩ to V
CC
/ 2
V
CC
= 6.5V, R
L
= 10kΩ to V
CC
/ 2
-15
10
35
60
85
0.10
0.05
0
-40
0
-40
TEMPERATURE (°C)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Low-Cost, Low-Voltage, PA Power Control
Amplifier for GSM Applications
Pin Description
PIN
1
2
NAME
SR1
SR2
FUNCTION
Inverting Input of Error Amplifier and Drain of V-to-I FET, Q1. Connect to supply side of current-sense
resistor, R
SENSE
, through gain resistor RG1.
Noninverting Input of Error Amplifier. Connect to load side of current-sense resistor, R
SENSE
, 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 1µA. Drive high or connect
to V
CC
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 to 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 0.1µF capacitor.
MAX4473
3
SHDN
4
5
6
7
8
PC
GND
SR3
OUT
VCC
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 (R
SENSE
), to the PA. The rail-to-rail
outputs of the error amplifier, A3, adjust the gain of the
PA until the voltage drop across R
SENSE
equals the
voltage drop across external gain resistor, RG1. The
voltage drop across RG1 sets the voltage drop across
R
SENSE
, 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 V
PC
/ 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:
I
CCPA
= ( V
PC
·
RG1 ) / ( 4
·
R
SENSE
·
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.
_______________________________________________________________________________________
5
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