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BQ78350-R1: Low-side FET, SMBUS Communication and FET_EN

Pietro Vignali
Intellectual 925 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350

Hello,

a new 7S circuit based on bq78350-R2 is using low-side FET.

The circuit is designed in a way that the SMBUS the ground is available and the communication persistent it at least a FET remains on, either CHG, DSG or PCH.

The problem arises during testing: issuing a FET_EN command to enter in manual mode set automatically all FETs OFF, and we loose the communication...

Is there a magic workaround to have the FET_EN command not to switch OFF all the FETs, but keeping them ON giving us the full freedom to play with them programmatically without loosing the communication in a Low-Side FET design ?

Thanks in advance

  • 0
    TI__Guru 54715 points
    Hi Pietro,
    No, the behavior of FET_EN is not adjustable. The feature in the bq78350 for individual FET control is HostFETControl, but you may have read that users have trouble with it: it has (slow) timing requirements, the other systems in the part may override it.
    Some users want to be sure the FETs stay off, you may have seen posts where they will pull the CHG and/or DSG low, this is OK but some method to reduce the resulting current is usually desired. But this is not really your request.
    To provide communication in any FET condition you may need isolation in your communication path.