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BQ79616-Q1: Problem with Balance LED indicators on CB Pins

Oguzhan GUVERCIN
Prodigy 10 points
Part Number: BQ79616-Q1

Tool/software:

Hi,

I'm working on a cell monitoring PCB with BQ79616-Q. And I would like to know if a cell is being balanced via LED indicator.

At first I tried a circuit like this given down below;

Since I'm working with LFP chemistry (i.e. 2.5V-3.6V range) the 10 ohm balance resistors doesn't drop enough voltage on them to turn on the LED's.

For example at 3.2V cell voltage voltage drop would be 1.6V which isn't enoguh to turn on most of the LED's on the market and I don't want to buy a new special LED for this.

My question to the forum is, is there a clever way to drive these LED's when IC's balancing a specific cell?

First idea that came to my mind was driving a PNP transistor from CB pins to turn on the LED's with a circuit like given down below;

When I simulate this circuit, there is a 1.85V voltage drop on LED and 12mA current through it. Which would be barely enough to get atleast some light on LED. See the simulation results down below;

Do you see any possible issues with this circuit?

Can you recommend a better way to do it?

Thanks in advance.

Best regards,

  • 0
    Prodigy 10 points

    Quick update about post above. The method I metioned doesn't work when two adjacent cells are being balanced.

    I need a solution that detects if CB pin is shorted or not rather then detecting voltage drop on balance resistor (hence my first solution)

    After seeing that I thought about a solution with NOT gates. I can put a NOT gate that can work when CB pins are shorted internally while balancing and drive the LED.

    But that solution requires low quasient current NOT gate that is able to work with low cell voltages. And this solution is also rather complex then solution with discrete components.

    Still wating for someone to come up with a simpler solution.

    Best regards,