BQ76PL455A-Q1: GPIO extension

Part Number: BQ76PL455A-Q1

Hello there,

We have an application in mind which could benefit from GPIO extension from 8 to
about 16 outputs. Would it be possible to use unused balancing outputs? I am not
sure about the best way to reference this to ground, since this is a level shifted topology.

Otherwise, I see only two options left:
a.) using some kind of port extender attached to the regular GPIO block.
b.) Converting a design with several stacks to CAN bus only, and the protocol would
carry the Ti specific command structure plus additional custom commands to address
larger GPIO space.

Thanks,

over 7 years ago

0 David Wiest Jr over 7 years ago

TI__Genius 11480 points

Hi Johannes,

The use of the EQ pins is not recommended. You can think of the EQ(n) pin as a switch between SNS(N) and SNS(N-1), so you will get something that mimics the cell voltages and EQ16 will be at a higher potential than EQ15. I recommend going with option 1. I think even a de-mux could work - you can use 1 GPIO as your signal and other GPIO's to control the multplexor. A variant of this is likely the best way to go.

0 Jo over 7 years ago in reply to David Wiest Jr

Intellectual 290 points

Hi David,

Thank you for advice, I will go for GPIO de-mux.

I plan an experimental setup, where each serial cell block in a battery pack is connected to a n-channel mosfet half bridge.
That way it mighty be possible to do fast charging and fast balancing in one pass, i.e starting a charging cycle on the whole
battery pack. The top and the bottom switches would be on then. As soon as single cell has reached 4.2V,
and additional controller on the BQ79PL455 can reconfigure the power path through a substring or through another single
cell even. The idea behind this to have a 100% balanced battery pack after each charging cycle without wasting energy
through bypass resistors.

If the idea works out to be practical, I won't use any of the regular balancing channels provided by the chip.

Regards,
Jo