Connecting to VBAT

[mstanisz]

Hi,

The nPM1100 Specification states in section 7.2 that:

An application should not be supplied directly from VBAT because it can disturb the battery charging
process and may cause incorrect behavior from the charger. Instead, VOUTB and/or VSYS should be used
to supply an application.

We are required to supply our PPG sensor with an LED supply of 3.3-4.5V.  We would supply the PPG with VSYS, but the 5.2V typical voltage is well past the absolute max of the PPG (5V).  Will we run into trouble by running the PPG LED supply off VBAT directly?

[ketiljo]

You can't connect the load to VBAT as it will upset the battery charger. The problem with VSYS is that it will exceed your maximum supply voltage when USB is connected. The maximum voltage the buck regulator can supply is 3.0 V, so you're in between this. 

The problem by having a sensor with a lower supply voltage level of 3.3 V, powered from a LiPo/Li-ion battery is that the battery voltage can be less than this. No easy solution to this problem, other than using a separate buck/boost regulator