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TIDUEB2A July 2022 – July 2022

2.2.6 Input and Battery Switchover Mechanics

This design provides an input and battery MUX that prioritizes the input adapter in all cases where the adapter voltage exceeds the UVLO setting of U1. When the UVLO threshold is triggered, the input adapter is disconnected from the system and the batteries are connected to power the system load. This prevents the batteries from discharging while an input adapter is present.

This threshold is set by the resistor divider consisting of R87 and R88. For U1 (input adapter connection) the UVLO thresholds are 1.13 V falling for turn off, and 1.23 V rising for turn on. For U7 (battery connection) the OV pin is connected to the same divider and the thresholds operate inversely. These thresholds are 1.13 V falling for turn on, and 1.23 V rising for turn off. In the schematic this voltage is connected to the net labeled UV/OV_SET. In the current schematic the switchover from input adapter to battery is triggered when VIN reaches 10.56 V and the switchover from battery to input adapter is triggered when VIN reaches 11.5 V.

Equation 3 shows an example of the resistor divider calculation:

B a t t e r y t o I n p u t A d a p t e r T r a n s i t i o n = \frac{1.23 V}{\frac{R 88}{R 87 + R 88}}

I n p u t A d a p t e r t o B a t t e r y T r a n s i t i o n = \frac{1.13 V}{\frac{R 88}{R 87 + R 88}}

R 87 = 5.97 k Ω, R 88 = 715 Ω

B a t t e r y t o I n p u t A d a p t e r T r a n s i t i o n = \frac{1.23 V}{\frac{715 Ω}{5.97 k Ω + 715 Ω}} = 11.5 V

Equation 3.

I n p u t A d a p t e r t o B a t t e r y T r a n s i t i o n = \frac{1.13 V}{\frac{715 Ω}{5.97 k Ω + 715 Ω}} = 10.56 V