Part Number:BQ25703A
I'm working on a handheld device with internal battery pack and charger IC. You only have to connect a USB to charge the battery pack. In my design I'm using the BQ25703A and I'm playing around with the EVM. I came across a problem for my design.
I have 4 series NiMH batteries and thus have the CELL_BATPRESZ set for 4 batteries. When starting in this setting the starting charging and system voltage are way to high! Only after setting the registers it will become correct. My first solutions was to pull the CELL_BATPRESZ to zero, set the registers and pull him up again, but the registers would still go to the high settings. I also tought about setting CELL_BATPRESZ for 1 or 2 series batteries and the starting outputs are low enough, but I can't start charging because of an over protection security that will keep setting after I reset it by pulling the register.
The only solution left in my mind is protect the circuit by hardware. (sorry for the drawing skills) I thought of something like the attached drawing. And I was wondering if this is really the only solution and/or there is still another option I hadn't thought of yet. And if in this design the OTG would still work.
I'm thinking of the worst case scenario. The battery is completely empty and thus the charger would start with high voltage when given power. I will power the circuit with the USB power and the powered intelligence will take the switches control.
When it start it should do:
- Set the charger registers for safe use, with low/none charging current to protect the USB from overcurrent
- Open switch 2
- Close switch 1
- Set the charger to charge, now that it is the only power consumer
My testing till now made me think the charger stays on as low as it has power (possible battery) but only turns on, on the adapter power. Is this correct?
THANK YOU!!!