Prioritizer provides low standby current backup battery switchover

The LTC4420, from Linear Technology, is a dual input monolithic power prioritizer for low current systems from 1.8 to 18V. It is said to provide backup switchover for keeping critical circuitry alive during brownout and power loss conditions.

The LTC4420 powers the load from the higher priority main supply such as a wall adapter or battery, switching to the backup supply – typically a battery or large-value capacitor – when needed.

The LTC4420 accommodates a range of power sources such as wall adapters, USB ports, supercapacitors, and stacked batteries with Li-Ion, alkaline or NiMH cells. By reducing device operating current to 3.6µA and the backup supply’s standby current drain to a low 0.32μA, the LTC4420 extends run time in portable battery-operated systems.

Unlike diode-OR products, little current is drawn from the inactive supply even if its voltage is greater than the active supply and the LTC4420 does not require the backup supply voltage to be lower than the main supply voltage.

Internal 500mA current-limited switches multiplex from the primary to the backup supply when the primary voltage falls below the adjustable switchover threshold. Switch control blocks reverse and cross conduction currents while minimising output voltage droop.

To reduce quiescent current, the backup supply’s resistive divider is connected to a strobed ground with a duty cycle that is adjustable down to 0.0015%, and an optional under voltage disconnect prevents discharged batteries. A freshness seal mode further lowers standby current to 0.12µA, minimising battery discharge during product storage and shipment. Reversed-battery voltages up to −15V are blocked from propagating to the load.

For temperature ranging from 0 to 70°C and −40 to 85°C, the LTC4420 is offered in thermally enhanced 12-pin MSOP and 3 x 3mm DFN packages.

Key features:

  • Connects highest priority valid supply to output
  • Internal dual 2Ω, 500mA (Min) current-limited switches
  • Low 3.6μA operating current
  • Low 0.32μA backup supply current
  • ±1.5% accurate adjustable switchover threshold
  • Blocks reverse and cross conduction currents
  • Reverse-battery protection to –15V
  • V2 freshness seal/ship mode
  • Overcurrent and thermal protection

Peggy Lee