STNS01PUR LDO spike during 5V connect

[AKrej.1]

I am seeing pretty poor performance from the LDO on the STNS01PUR when 5V is attached to the charging chip. When 5V is applied there is an initial moderate spike in the LDO output, followed by a much bigger and prolonged spike after several ms. The relative size of the spike seems to increase with both a more discharged battery or a higher load on the LDO. It seems like the transitions from battery to external supply is not being handled smoothly.

I've attached scope traces under moderate conditions (500mAh battery @ 3.8V, ~40mA load) that still show an almost 500 mV spike for ~1ms. 5V is being supplied by a laptop USB port.

The yellow trace is the LDO output and the blue trace is the 5V input.

 

[FLIBR.1]

Hello

The STNS01 is designed to have a very low quiescent current during the operation in Battery mode, so the LDO, being a low quiescent current, has a slow dynamic response versus line(input variation) variation. This creates the problem you are facing.

However , there is an application workaround that reduces a lot this spike.

In the below picture, you can see an RC network (in blue) consisting of a 10uF cap and 1 Ohm resitor connected between IN and SYS. This should recuce a lot the issue.

 

I hope this helps.