Triple-supply controller simplifies power system design, protects against reversed inputs

December 11, 2012 // By Paul Buckley
Linear Technology Corporation has introduced a triple-supply prioritized PowerPath controller for 2.5 V to 36 V systems.

The LTC4417 controller selects the highest priority valid supply among three inputs to power the load. Priority is defined by pin assignment, while a supply is considered valid after it has been inside a voltage window set by 1.5% accurate undervoltage and overvoltage thresholds for 256 ms. The LTC4417 greatly simplifies designs, deriving power from multiple, disparate voltage sources common in handheld and high availability electronics. In such systems, a prioritizer is a better solution than a simple diode-OR, especially when the preferred power source is not the highest voltage. The LTC4417 controller also protects the load from reversed inputs to −42 V.

PowerPath switching is implemented by external back-to-back P-channel MOSFETs protected by integrated 6 V gate clamps. Carefully designed fast switch control blocks reverse and cross-conduction current while preventing output voltage droop. A low 28 µA operating current, sub-1 µA draw from the lower standby supplies, and a shutdown mode make the controller ideal for battery backup systems. The LTC4417’s wide operating range accommodates a wide range of power sources such as wall adapters, USB, Firewire, supercapacitors, and batteries such as lead-acid, Li-Ion and stacked NiCd. Built-in cascading support extends the LTC4417 prioritization beyond three supplies. To minimize start-up inrush current, the first connection is soft-started. Open-drain outputs indicate the supplies that are within their valid voltage window. Undervoltage and overvoltage hysteresis is adjustable with a single resistor.

Specified over the full commercial, industrial and automotive temperature ranges, the LTC4417 is offered in 24-pin QFN (4 mm x 4 mm) and 24-lead narrow SSOP packages. Pricing begins at $3.05 each for 1,000-piece quantities and the device is available today in production quantities.

More information about the PowerPath controllers at
www.linear.com/powerpath_controllers