BQ76925: Soldering cells directly to board

JPAlleyne

Part Number: BQ76925

We are currently implementing a 6S (vbat 25.2V max)system with this chip. Due to space constraints we need to solder balance wires from board directly to the cells. Is there a particular order that we would need to solder the cells in so as to not damage to the IC?

Side note, we do have a current amplifier arrangement for powering the microcontroller using VBAT as the current source through a PFET and V3P3 as the reference voltage.

over 5 years ago

0 Matt Sunna over 5 years ago

TI__Guru* 81034 points

Hi JP,

This isn't explained in the datasheet, but I think this thread may have the answer you need: https://e2e.ti.com/support/power-management/f/196/t/744068

There is also a recommended cell connection sequence in the EVM User Guide: http://www.ti.com/lit/ug/sluu514a/sluu514a.pdf

Best regards,

Matt

0 JPAlleyne over 5 years ago in reply to Matt Sunna

Expert 1565 points

Hi Matt,

Thanks for the response. We were going: BATT-, CELL1, CELL2.. CELLN, BATT+ with the connections. We have had a few of them act strangely (namely the regulator voltage output would not be 3.3V... it'd be 4.1-4.3V and sometimes 1V). When I remove the last two cells, I usually get a stable 3.3V. This issue has not been seen across all batteries, but I've seen this behavior on a few. Do you think this can be caused by the order I connect the cells?

0 Matt Sunna over 5 years ago in reply to JPAlleyne

TI__Guru* 81034 points

Hi JP,

That does seem like a strange behavior. Is it possible something is driving a voltage on the regulator pin? I'm not sure if cell connection order could cause this.

Regards,

Matt

0 JPAlleyne over 5 years ago in reply to Matt Sunna

Expert 1565 points

Hi Matt,

I've attached a portion of the schematic below. VCC 3V3 is driving the microcontroller. Is there possible instability without the capacitors on VCTL/ V3P3?

0 Matt Sunna over 5 years ago in reply to JPAlleyne

TI__Guru* 81034 points

Hi JP,

If there is no capacitor on V3P3, I think this will cause instability. In section 6 of this app note (https://www.ti.com/lit/an/slua619b/slua619b.pdf), it discusses the impact of the amount of quiescent current during startup which might explain the observed behavior.

Best regards,

Matt

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BQ76925: Soldering cells directly to board