LTC1957-2

` Dual Band RF Power Amplifier Control (LTC1957-2)
` Internal Schottky Diode Detector with Improved Dynamic Range vs the LTC1757A
` Wide Input Frequency Range: 850MHz to 2GHz
` Autozero Loop Cancels Offset Errors and Temperature Dependent Offsets
` Wide V<sub>IN</sub> Range: 2.7V to 6V
` Allows Direct Connection to Battery
` RF Output Power Set by External DAC
` Fast Acquire After Transmit Enable
` Internal Frequency Compensation
` Rail-to-Rail Power Control Outputs
` Power Control Signal Overvoltage Protection
` Low Operating Current: 1mA
` Very Low Shutdown Current: <1A
` Available in a 8-Pin MSOP Package (LTC1957-1) and 10-Pin MSOP (LTC1957-2)
` Pin Compatible with the LTC1757A-X
` Improved Start Voltage Accuracy and Range
` Improved PCTL Input Filtering

· Single and Dual Band GSM/GPRS Cellular Telephones
· PCS Devices
· Wireless Data Modems
· U.S. TDMA Cellular Phones

V_IN to GND .................................................. 0.3V to 6.5V
V_PCA, V_PCB Voltage ........................................ 0.3V to 3V
PCTL Voltage ................................... 0.3V to (V_IN + 0.3V)
RF Voltage ............................................. (V_IN 2.2V) to 7V
IV_CC, Continuous ........................................................... 1A
IV_CC, 12.5% Duty Cycle ............................................... 2.5A
SHDN, TXEN, BSEL
Voltage to GND ................................ 0.3V to (V_IN + 0.3V)
I_VPCA/B, 25% Duty Cycle ............................................. 20mA
Operating Temperature Range (Note 2) ... 30°C to 85°C
Storage Temperature Range .................. 65°C to 150°C
Maximum Junction Temperature ............................... 125°C
Lead Temperature (Soldering, 10 sec)...................... 300°C

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 integrated 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 of LTC1957-2 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 temperature by an autozero control loop, allowing accurate low power programming. The shutdown feature disables the part and reduces the supply current to <1A.