PowerPath prioritizer eases power-system design with multiple disparate input sources

Linear Technology has introduced the LTC4417, a triple-supply prioritized PowerPath controller for 2.5 to 36 V systems. The controller selects the highest priority valid supply among three inputs to power the load. The controller defines priority by pin assignment and considers supplies valid that have been inside a voltage window set by 1.5% accurate under-voltage and over-voltage 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 option 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 ?42V. The company implements its PowerPath switching by means of 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-1μA draw from the lower standby supplies, and a shutdown mode make the controller highly attractive for battery backup systems. The LTC4417's wide operating range accommodates a broad 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. Under-voltage and over-voltage hysteresis is adjustable with a single resistor. Specified over the full commercial, industrial, and automotive temperature ranges, the LTC4417 is available in 24-pin QFN (4 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. Evaluation circuit boards are also available. Summary of Features: LTC4417

• Connects highest priority valid supply to output
• 256 ms long, 1.5% precise over-voltage and under-voltage validation
• Wide operating voltage range: 2.5 to 36 V
• ?42 V protection against reversed battery
• Blocks reverse and cross conduction
• Fast switchover minimizes output-voltage droop
• Low 28 μA operating current
• < 1 μA current draw from supplies less than V_OUT
• Adjustable over-voltage and under-voltage hysteresis
• Cascadable for additional input supplies
• Available in 24-lead narrow SSOP and QFN packages