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Part Number: BQ28Z610
I am using the BQ28z610 in a system (not pack) application. The battery is external to the main PCB which has the gauge on it. The pack already has charge/discharge protection therefore I'm not using any of the pack protection elements so the schematic is simplified. Schematic attached. The pack is 2S1P configuration 8.4V (4.2V/cell) 600mAh. The battery will be embedded in the device and is not user replaceable.
The Battery voltage gauge in BqStudio always shows 0V and Cell 1 voltage and Cell 2 voltage are always 0, but Bat pin voltage and Pack pin voltage are correct.
I have disabled any protections in the protections registers, since I don't need them. I have also raised the limits on the over-voltage and under-voltage protection. I have cleared the CC0 bit to enable "single cell" mode. I have also disabled balancing.
If I use an external power supply to drive a little voltage to the pins instead of using the battery, I get a good voltage reading when less than 6V. When the supply is set to > 6V, then BQstudio shows 0V as the voltage in registers 0x08/0x09.
Picture of the schematic is attached. Is this device just not capable of such a configuration or is it just a matter of getting the register configuration correct?
I have followed the recommendation in this thread:
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In reply to -Terry:
The BQ34Z1x0 was my first choice however being a TSSOP it was just too large. I was just too space constrained and it required too much support circuitry for what I was getting. I could make the whole circuit of the BQ28z610 fit in the same space as the courtyard of the BQ34Z1x0 IC itself. It's too bad the BQ34 series doesn't come in smaller packages. Anyhow, I saw another thread where someone asked the question "can I use this with a 2S pack without the center balance tap" and they got a resounding yes, just put it in 1Cell mode and change your registers. There are other reasons why we can't bring out the center balance connection. Anyhow, water under the bridge.
Luckily I don't need "excellent" gauging and I ended up using a resistor divider (47K x 2) from VC2 to GND with the midpoint of the divider going to VC1. That gets me in the ball park. At least I'm reading "something". Whether it is super accurate or not doesn't matter for my application. As I go through the learning process, I'll find out how good or bad the workaround really is.
In reply to Jason Gurley61:
Hmmm, that sounds odd, I don't know why it would be drawing that much current. Let me ask around, but offhand I'm not sure what might be causing it, or how to reduce it further through settings.
I don't see the current on VC1 until I do a register read from BQStudio. I see about a 2V deflection from 4V down to about 2 volts when a do any sort of reading of registers in BQStudio.
HA! I just figured it out. The I2C lines are pulled up to VC1 net when P2 and P3 are shorted!
I changed to using external I2C pull-ups since I'm using an EV2300 and that fixed it!
Thank you for your help!
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