LTC1957-1_15 Datasheet, PDF (1/16 Pages) Linear Technology – Single/Dual Band RF Power Controllers with 40dB Dynamic Range

LTC1957-1/LTC1957-2
Single/Dual Band RF Power
Controllers with 40dB Dynamic Range
FEATURES
DESCRIPTIO
s _{Dual Band RF Power Amplifier Control (LTC1957-2)}
s _{Internal Schottky Diode Detector with Improved}
Dynamic Range vs the LTC1757A
s _{Wide Input Frequency Range: 850MHz to 2GHz}
s _{Autozero Loop Cancels Offset Errors and}
Temperature Dependent Offsets
s _{Wide VIN Range: 2.7V to 6V}
s _{Allows Direct Connection to Battery}
s _{RF Output Power Set by External DAC}
s _{Fast Acquire After Transmit Enable}
s _{Internal Frequency Compensation}
s _{Rail-to-Rail Power Control Outputs}
s _{Power Control Signal Overvoltage Protection}
s _{Low Operating Current: 1mA}
s _{Very Low Shutdown Current: < 1µA}
s _{Available in a 8-Pin MSOP Package (LTC1957-1)}
and 10-Pin MSOP (LTC1957-2)
s _{Pin Compatible with the LTC1757A-X}
s _{Improved Start Voltage Accuracy and Range}
s _{Improved PCTL Input Filtering}
U
APPLICATIO S
s _{Single and Dual Band GSM/GPRS Cellular Telephones}
s _{PCS Devices}
s _{Wireless Data Modems}
s _{U.S. TDMA Cellular Phones}
The LTC^®1957-2 is a dual band RF power controller for
power amplifiers operating in the 850MHz to 2GHz range.
The input voltage range is optimized for operation from
a single lithium-ion cell or 3× NiMH. Several functions
required for RF power control and protection are inte-
grated in one small 10-pin MSOP package, thereby
minimizing PCB area.
The LTC1957-1 is a single output RF power controller
that is identical in performance to the LTC1957-2 except
that one output (V_PCA) is provided. The LTC1957-1 can
be used to drive a single RF or dual channel module with
integral multiplexer. This part is available in an 8-pin
MSOP package.
RF power is controlled by driving the RF amplifier power
control pins and sensing the resultant RF output power
via a directional coupler. The RF sense voltage is peak
detected using an on-chip Schottky diode. This detected
voltage is compared to the DAC voltage at the PCTL pin
to control the output power. The RF power amplifier is
protected against high supply current and high power
control pin voltages.
Internal and external offsets are cancelled over tempera-
ture by an autozero control loop, allowing accurate low
power programming. The shutdown feature disables the
part and reduces the supply current to < 1µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
LTC1957-2 Dual Band Cellular Telephone Transmitter
68Ω
V_IN ^33pF
LTC1957-2
1
10
V_IN
V_CC
Li-Ion
2
RF
9
V_PCA
3
8
SHDN
SHDN
V_PCB
4
7
BSEL
BSEL
TXEN
TXEN
5
GND
6
PCTL
900MHz
RF PA
DIRECTIONAL
COUPLER
DIPLEXER
50Ω
DAC
1.8GHz /1.9GHz
RF PA
1957 TA01
1