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18 V Prioritizer Provides Back-up Battery Switchover Solution

08 September 2016

Linear Technology Corporation has introduced the LTC4420, a dual-input monolithic power prioritizer for 1.8 V to 18 V systems. The LTC4420 normally powers the load from the higher priority main supply, such as a wall adapter or battery, switching to the back-up supply—typically a battery or large-value capacitor—during primary brownout or power loss conditions.

LTC4420 power prioritizer. Source: Linear Technology Corp.    LTC4420 power prioritizer. Source: Linear Technology Corp.

With up to 18 V operating capability, the LTC4420 accommodates a wide 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 3.6 µA and the back-up supply’s standby current drain to a low 0.32 μA, the LTC4420 extends run time in portable battery-operated systems.

Unlike other solutions, the LTC4420 does not require the back-up supply voltage to be lower than the main supply voltage. When the back-up supply voltage is higher than the main supply voltage, a prioritizer is a better solution than a simple diode-OR, as the prioritizer does not necessarily draw current from the highest voltage supply. Internal 500 mA (min.) current-limited switches multiplex from the primary to the back-up supply when the primary voltage falls below the adjustable switchover threshold. Carefully designed break-before-make fast-switch control blocks reverse and cross conduction currents while minimizing output voltage droop.

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

Specified over the 0° C to 70° C commercial and −40° C to 85° C industrial temperature ranges, the LTC4420 is offered in thermally enhanced 12-pin MSOP and 3 mm x 3 mm DFN packages. Pricing for 1,000 pieces starts at $2.95 each.

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