The LTC4420 provides undervoltage monitoring and optional disconnect of the V2 backup supply in addition to the LTC4419 functionality. Disconnecting V2 on undervoltage is important in preventing deep discharge and potential damage to rechargeable batteries. To reduce V2 divider current, a strobed ground is provided with a low duty cycle between 0.0015% to 0.1%. The scope shot shows the output switching initially from V1 to V2 when V1 falls below the adjustable switchover threshold. Subsequently, the output is also disconnected from V2 when V2 falls below its undervoltage threshold. The LTC4420 has only one auxiliary comparator, which is used in this circuit to provide an early fail warning on V1.