D22 and D23 on BQ76930EVM

Dan Bishop

Prodigy 195 points

Other Parts Discussed in Thread: BQ76930EVM

Hello,

What is the purpose of D22 and D23 on the BQ76930EVM that connect C5 to VC5X (VC5X pin)and C10 to VC10X (BAT pin)?

Thanks.

Dan.

over 10 years ago

0 Andy Chen over 10 years ago

Intellectual 580 points

Hi Dan, these are present to ensure that VC10 stays within a Vf of BAT, and similar with VC5 and VC5x. This is to avoid creating undesirable biasing conditions on VC10 and VC5 that could interfere with or damage the ADC functionality during transient events.

Allen

0 Dan Bishop over 10 years ago in reply to Andy Chen

Prodigy 195 points

Hi Allen,

So from a protection point-of-view, VC10 could only be a higher voltage than BAT (requiring the diode) or we don't care if it is lower (and same with VC5 / VC5x)?

Dan.

0 Andy Chen over 10 years ago in reply to Dan Bishop

Intellectual 580 points

Hi Dan, in general you don't want VC10 to go higher than BAT, and same with VC5 versus VC5x. Lower is OK.

Allen

0 Dan Bishop over 10 years ago in reply to Andy Chen

Prodigy 195 points

Hi Allen,

I saw from another post that there was some concern about VC5B rising faster than VC5X when cells were connected and cell balancing FETs were in an ambiguous control state. Protection was recommended. Would you suggest another PN diode between VC5B andVC5X or would a Zener diode be more appropriate?

0 Andy Chen over 10 years ago in reply to Dan Bishop

Intellectual 580 points

Hi Dan,

Actually, this should be what the existing diode will help you avoid - as VC5B rises, if it gets to a Vf above VC5x, VC5x will follow thanks to that Schottky. The minor difference from that Vf is negligible.

Thanks!
Allen

0 Dan Bishop over 10 years ago in reply to Andy Chen

Prodigy 195 points

Hi Allen,

OK. I see that VC5X is almost the same node as C5 except for the filter. So for BQ76930EVM, VC5X might take longer to rise because of R59 and C35 (10uF) so D22 should supplement current. Perhaps in the case I saw, the person did not have any diode in place which was causing his trouble.
Thanks.
Dan.

Power management

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D22 and D23 on BQ76930EVM