LTC1340

The LTC 1340 is a varactor diode driver designed to generate5V varactor drive from a single 3V or higher voltage supply.It includes a low noise amplifier with an internal gain of 2.3and a self-contained charge pump to generate output volt-ages above the input supply. The amplifier input stageincludes a built-in offset voltage that allows the output voltageto swing to ground without requiring OV on the input. Thisfeature maintains the phase detector within its linear range ofoperation. The LTC1340 requires only three external surfacemount capacitors to implement a complete varactor drivermodule.

The LTC1340 features output referred noise of 15µVRMS,minimizing frequency deviation in PLL frequency synthe-sizer systems. Supply current is 400µA typically with a 3Vsupply, and drops to 1µA in shutdown, maximizing operatinglife in battery-powered systems. Amplifier bandwidth is user-adjustable from 10kHz up to 500kHz and the output typicallysinks or sources 20µA, allowing fast output signal changeswith a typical varactor load. The amplifier input features rail-to-rail input common mode range, allowing itto interface with the output of virtually any phase detectorcircuit.

The LTC1340 is available in MS8 and SO-8 packages.