Prioritizer chooses power input for handhelds

Linear Technology Corp. debuts the LTC4417 PowerPath controller. Designed for 2.5V to 36V systems, the controller chooses the highest priority valid supply among three inputs to power a 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 per cent accurate under-voltage and over-voltage thresholds for 256ms.

The device derives power from multiple, disparate voltage sources common in handheld and high availability electronics. It replaces simple diode-ORs, especially when the preferred power source is not the highest voltage. The controller also protects the load from reversed inputs to −42V.

PowerPath switching is implemented by external back-to-back P-channel MOSFETs protected by integrated 6V gate clamps. Fast switch control blocks reverse and cross-conduction current while preventing output voltage droop. A 28μA operating current, sub-1μA draw from the lower standby supplies, and a shutdown mode make the controller suited 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 prioritisation beyond three supplies.

To minimise start-up inrush current, the first connection is soft-started. Open-drain outputs indicate the supplies that are within their valid voltage window. Under-voltage and over-voltage hysteresis is adjustable with a single resistor.

The LTC4417 PowerPath controller is specified over the full commercial, industrial and automotive temperature ranges and comes in 4mm x 4mm 24-pin QFN and 24-lead narrow SSOP packages. It is priced at Rs.161.38 ($3.05) each for 1,000-piece quantities. It is available today in production quantities.