Soft Power Switch (SPX-17870) turns on and off while charging (should stay on)

SPARK-X
1

Hi, I am trying to use the [SPX-17870 soft power switch in a Raspberry Pi project and I have a question about charging the battery through the cut-off portion of the switch circuit. I am experiencing unexpected behavior when I plug in the charger to wall power. The switch ends up oscillating between off and on if the power was plugged in and the device is off. This disrupts the charging to the battery. I think the intended behavior is for the charger to remain on the entire duration until the battery is detected to be full.

Halfway down the [README in the hardware repo of this product, there is a claim that says:

The Soft Power Switch supports battery charging. If the target device has onboard LiPo charging, current can be passed back through the cut-off circuit and charge the battery.

From this statement, I made several inferences. Originally, I placed the power switch between the charger and the Raspberry pi, but this statement implies that the soft power switch can go between the battery and the charger. Like so:

mCyOjis.png723×446 67.1 KB
https://i.imgur.com/mCyOjis.png

In this setup, I am using a single 18650 cell lithium polymer battery hooked into J10. On J2, is a [sparkfun battery babysitter that leads to a buck/boost converter and finally into a Raspberry Pi 3A+. Sense/ctrl of J3 is hooked up to GPIO6 of the raspberry pi and that pin is configured with the gpio-poweroff overlay (it is a hi-z INPUT when the device is on and pulled down to ground as an OUTPUT when the device is halted). Fast off is unconnected and GND is hooked up to a ground on the RPI.

If I have the device turned off and I plug in a USB charger into the babysitter, I notice that the device will charge for a second, then shutoff, and then turn back on and repeat. This does not happen if I disconnect the Sense/ctrl pin, but I can’t do that permanently because I need it to operate the switch.

So my final question is, am I using this product as intended and/or misunderstanding what features it is capable of?](SparkFun Battery Babysitter - LiPo Battery Manager - PRT-13777 - SparkFun Electronics)](GitHub - sparkfunX/Soft_Power_Switch)](Soft Power Switch - SPX-17870 - SparkFun Electronics)

2

Bump. Is there anyone who can help me with this? Thanks

3

I’ve come to the conclusion that the power switch circuit simply is not designed to support charging through the body diode of the top mosfet and this is something that should be taken off of the advertisement of the product. I’ve moved the switch to be between the battery and before the charging port so I can avoid this situation.

Is there no staff handling things here? Not even a “we’re looking into it” or “we don’t know sorry”?? I’m very disappointed in the sparkfun experience. Not many of the products work as you would expect, there’s very little documentation, and apparently no support for customers.