SLVAET3 October 2021 TPS8802
The smoke and CO system connects VBST to VCC to allow battery voltages down to 2.0 V. Here the MCU LDO is set to 1.8 V, a low voltage that can be powered without the boost converter being enabled. The boost converter can be enabled to 2.7 V, 3.8 V, or 4.7 V to supply the IR LED through PLDO with a low-leakage (0.1 µA) Schottky diode. The blue LED is supplied by the LED LDO to support the higher blue LED forward voltage. The CO amplifier is continuously enabled to track the slowly-varying CO concentration signal.