Power supply IC generates low-noise bipolar (+/-) power rails

September 01, 2015 // By Graham Prophet
LTC3265 is a high voltage, highly integrated, low noise dual output power supply IC which takes a single positive input supply (VIN_P) and generates low noise bipolar rails up to ±2•VIN_P without any inductors. High voltage boost and inverting charge pumps deliver low noise dual outputs with post-regulating ±50 mA LDOs

The device includes a boost doubling charge pump, an inverting charge pump and two low dropout (LDO) regulators. The boost charge pump has a 4.5V to 16V input range and powers the positive LDO post regulator from its output, VOUT+. The inverting charge pump has a wider input range (4.5V to 32V) which may be connected to either the boost input or output. The negative LDO post regulator is powered from the output of the inverting charge pump, VOUT-. The LTC3265 is suited for a variety of applications that require low noise bipolar supplies from a high voltage input, such as industrial/instrumentation low noise bias generators, portable medical equipment and automotive infotainment systems.

The positive and negative LDO regulators can source up to 50 mA of output current each with 100 µVRMS output noise, and their output voltages can be independently adjusted from ±1.2V to ±32V using external resistor dividers to generate symmetric or asymmetric output supply rails. The internal charge pumps of the LTC3265 function in either low quiescent current Burst Mode operation for highest efficiency, or constant frequency mode for lowest noise. In Burst Mode operation, the LTC3265 draws 135 µA of quiescent current with both LDO regulators on at no load. In constant frequency mode the part operates at a fixed 500 kHz, or at a programmed value between 50 kHz and 500 kHz using an external resistor. Other IC features include low external parts count, stability with ceramic capacitors, soft-start circuitry to prevent excessive current flow during start-up, plus short-circuit and thermal protection.

The LTC3265 is available in a low profile (0.75 mm) 3 x 5 mm 18-lead DFN package and a 20-lead TSSOP package, both with a backside thermal pad. The E- and I-grade operating junction temperature range is -40°C to 125°C regardless of package. The H grade operates from -40°C to 150°C, while the MP grade operates from -55°C to 150°C. Pricing starts at