bq76940 Internal cell balance not working

Tiger Chen

Other Parts Discussed in Thread: BQ76920, BQ76930

hi,

today i tried to set cell balance e.g. CELLBAL1 set to 0x03, CELLBAL2 and CELLBAL3 set to 0, on monitoring these cell voltage i don't see voltage drop across these cells, because the DEVICE_XREADY flag is 1 ?

cheers,

Tiger

over 10 years ago

0 Ryan Brown2 over 10 years ago

Intellectual 795 points

From what I understand only the BQ76920 has built in cell balancing, your model requires external components to do the actual balancing.

0 Tiger Chen over 10 years ago in reply to Ryan Brown2

Intellectual 750 points

as per my understanding all 3 models has built-in cell balance feature, just very small current ~5mA on 76940 and TI recommend external balance on 76940.

0 Ryan Brown2 over 10 years ago in reply to Tiger Chen

Intellectual 795 points

Yep your right. 5mA is indeed pretty weak.

0 fhoude over 10 years ago

TI__Mastermind 23116 points

It sounds like you got some sort of Permanent Fail that caused the XREADY bit to be set. If the XREADY is set.

In page 26 of the bq76930 Datasheet, there is a note that says the following:

"NOTE

All cell balancing control bits in CELLBAL1, CELLBAL2, and CELLBAL3 are automatically

cleared under the following events, and must be explicitly re-written by the host

microcontroller following clearing of the event:

• DEVICE_XREADY gets set

• Enters NORMAL mode from SHIP mode"

-Francis H

Power management

Power management forum

bq76940 Internal cell balance not working