Step-Down Supply Dissipates Low Power, Needs No Inductors

The LTC3256 from Linear Technology Corporation is a highly integrated, high-voltage, low-noise, dual-output power supply, which takes a single positive input and generates 5 V and 3.3 V step-down supplies with high efficiency and no inductors.

The device features a 5.5 V to 38 V input voltage range and includes independently enabled dual outputs: a 5 V 100 mA supply, and a 250 mA 3.3 V low-dropout (LDO) regulator, for a total of 350 mA available output current. This combination of regulators offers much lower power dissipation than a dual-LDO solution. For example, at 12 V VIN and maximum load on both outputs, power dissipation is decreased by over 2 W with the LTC3256, thus reducing significant heat and input current.
The LTC3256 is engineered for diagnostic coverage in ISO26262 systems and incorporates numerous safety and system-monitoring features. The device is suited for applications requiring low noise, low power rails from a high-voltage input such as automotive ECU/CAN transceiver supplies, industrial and telecom housekeeping supplies, and general-purpose, low-power 12 V to 5 V and 3.3 V conversion.
The LTC3256 maximizes 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 minimize conducted and radiated EMI. The device offers low quiescent current of only 20 μA with both outputs regulating (no load) and 0.5 μA in shutdown. The integrated watchdog timer, independent power-good outputs, and reset input ensure reliable system operation and enable fault monitoring. A buffered 1.1 V reference output enables system self-testing diagnostics for safety-critical applications.
The LTC3256 also has additional safety features, including over-current fault protection, over-temperature protection and tolerance of 38 V input transients.


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