LTC1757A

The LTC1757A-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 temperature by an autozero control loop, allowing accurate low power programming. The shutdown feature disables the part and reduces the supply current to <1µA.

Applications

• Single/Dual Band GSM Cellular Telephones
• PCS Devices
• Wireless Data Modems
• TDMA Cellular Telephones