High voltage step-down charge pump offers lower power dissipation

Linear Technology has announced the LTC3256, a highly integrated, high voltage low noise dual output power supply, which takes a single positive input and generates 5V and 3.3V step-down supplies with high efficiency and no inductors. The device features a wide 5.5V to 38V input voltage range and includes independently enabled dual outputs: a 5V 100mA supply, and a 250mA 3.3V low-dropout (LDO) regulator, for a total of 350mA available output current. This combination of regulators offers much lower power dissipation than a dual-LDO solution. For example at 12V VIN and maximum load on both outputs, power dissipation is decreased by over 2W with the device, thus reducing significant heat and input current. The device is engineered for diagnostic coverage in ISO26262 systems and incorporates numerous safety and system monitoring features. The device is well-suited for a variety of applications requiring low noise, low power rails from a high voltage input such as automotive ECU/CAN transceiver supplies, industrial/telecom housekeeping supplies, and general-purpose low-power 12V to 5V and 3.3V conversion. It maximises efficiency by running the charge pump in 2:1 mode, over as wide an operating range as possible, and automatically switches to 1:1 mode as needed, consistent with VIN and load conditions. Controlled input current and soft switching minimise conducted and radiated EMI. The device offers low quiescent current of only 20µA with both outputs regulating (no load) and 0.5µA in shutdown. The integrated watchdog timer, independent power good outputs and reset input ensure reliable system operation and enable fault monitoring. A buffered 1.1V reference output enables system self-testing diagnostics for safety critical applications. The device also has additional safety features including overcurrent fault protection, overtemperature protection and tolerance of 38V input transients.