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Prioritizer chooses power input for handhelds

Posted: 19 Dec 2012     Print Version  Bookmark and Share

Keywords:controller  power  prioritizer 

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.

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