Increasing TPS63001 Under Voltage lockout from 1.8V to 2.5V for use with LiFePO4 cell
Accordong the datasheet the quiescent current of VINA is just 40uA typical. You may even need 2 diodes to get enough voltage drop with that low current.

Another solution might be using a PNP transistor, which cuts off the supply to VINA when the battery voltage becomes too low.







simulate this circuit &ndash; Schematic created using CircuitLab