BQ25120A: Create a soft-latch circuit for the load switch using an MCU

Hi Josh,

You could wire in the SYS pin to VINLS and use the internal loadswitch of the BQ25120A therafter, you can control the loadswitch through the MCU. 

What is the case where the loadswitch would need to turn OFF the MCU supply? Also if you could share more details on recovery, that would be great. 

Regards,

Gautham

Hi Gautham,

Essentially, it's a wearable where the MCU controls all sensors, BLE, etc... I am using the BQ25120A with inductive charging for power management. The battery is integrated into the device. I am trying to find a way to implement a smart switch (i.e. a button that controls power with long button presses and controls functions of MCU with short button presses once on). Ideally, I would like to use the Load Switch provided in the BQ25120A to assist with that.

Best, Josh

Hi Josh,

I get it. I think one option would be to use the internal Wake1/ Wake2 timers if the timings work for you for short and long press action along with a longpress to send the device into shipmode (essentially) turning OFF the product. 

You could also mirror the /MR pin to /PG pin and connect it a micro to detect the button state. 

For the implementation on shipmode, I have included a blog I wrote on this topic. You could also select between resetting your micro or use it to turn OFF the product.

Let us know if you have any questions. 

https://e2e.ti.com/blogs_/b/powerhouse/posts/pull-the-tab-how-to-implement-ship-mode-in-your-lithium-ion-battery-design

Regards,

Gautham

Hi Gautham,

My other issue is that my MCU requires 3.3V and the default SYS output is 1.8V.  What options do I have to accommodate my MCU 3.3V rail? 

Hi Joshua,

We have the BQ25121A which has a default of 2.5V. Will that work for you?

https://www.ti.com/product/BQ25121A

Regards,

Gautham

2.5V will not work. 3.3V is needed. Do you have any products to support that voltage rail?

Hi Joshua,

In that case, I would recommend using a BQ25155 + TPS62808 which can support 3.3V with a small solution size. 

This would be similar to the PMP21884 https://www.ti.com/tool/PMP21884

Regards,

Gautham

Hi Gautham,

That makes a lot of sense! What I am doing today is using the PMID output of the BQ25120A with TPS70933 (similar to the TPS62808) to get a 3.3V rail. Is your suggestion to use the SYS pin on the enable pin of the regulator?