LTC1757A-2_15 Datasheet, PDF (1/16 Pages) Linear Technology – Single/Dual Band RF Power Controllers

LTC1757A-1/LTC1757A-2
Single/Dual Band
RF Power Controllers
FEATURES
DESCRIPTIO
s _{Dual Band RF Power Amplifier Control (LTC1757A-2)}
s _{Improved Internal Schottky Diode Detector}
s _{Wide Input Frequency Range: 850MHz to 2GHz}
s _{Autozero Cancels Initial Offsets and Temperature}
Dependent Offset Errors
s _{Wide VIN Range of 2.7V to 6V 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 _{RF PA Supply Current Limiting}
s _{Battery Overvoltage Protection}
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 (LTC1757A-1)}
and 10-Pin MSOP (LTC1757A-2)
U
APPLICATIO S
s _{Single/Dual Band GSM Cellular Telephones}
s _{PCS Devices}
s _{Wireless Data Modems}
s _{TDMA Cellular Telephones}
, LTC and LT are registered trademarks of Linear Technology Corporation.
The LTC^®1757A-2 is a dual band RF power controller for
RF power amplifiers operating in the 850MHz to 2GHz
range. The LTC1757A is pin compatible with the LTC1757
but has improved RF detection 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 integrated in one small 10-pin
MSOP package, thereby minimizing PCB area.
The LTC1757A-1 is a single output RF power controller
that is identical in performance to the LTC1757A-2 except
that one output (V_PCA) is provided. The LTC1757A-1 can
be used to drive a single RF channel 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 voltage and 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.
TYPICAL APPLICATIO
LTC1757A-2 Dual Band Cellular Telephone Transmitter
68Ω
V_IN ^33pF
LTC1757A-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
1757A TA01
1