Engineering 101

Dual output power supply generates without inductors

Announced by Linear Technology, the LTC3256, a highly integrated, high voltage low noise dual output power supply, which takes a single positive input and generates 5 and 3.3V step-down supplies with high efficiency and no inductors. The device features a wide 5.5-38V input voltage range and includes independently enabled dual outputs: a 5V 100mA supply, and a 250mA 3.3V 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 12VIN and maximum load on both outputs, power dissipation is decreased by over 2W 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 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 12 to 5V and 3.3V conversion.

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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 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 LTC3256 also has additional safety features including overcurrent fault protection, overtemperature protection and tolerance of 38V input transients.

Datasheets available:

Linear Technology LTC3256 datasheet

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