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BQ77905: bq77905 ctrc and CHGU pin

bar greidy
Intellectual 460 points
Part Number: BQ77905


Hello,

Please advice for the bellow two issues if using BQ77905 non stacked, only 1 ic used for 3s:

 

1. Is the CHGU pin should be left unconnected - floated? or tied to?

2. a verification for CTRC pin, Is Enable state when CTRC <=0.6V And in order to shut down the 2 mosfets with CTRC pin, will it need voltage above 0.6v?

Thank you

  • 0
    TI__Guru 54715 points
    Hi Bar,
    1. CHGU is an output, it should be left unconnected.
    2. CTRC will control only the charge related outputs (CHG and CHGU).
    Below 0.6V the charge outputs are enabled, see the VCTR1 specification.
    To disable however you must take the input above 2.04V, see the VCTR(DIS) specification (actually 2.04 to VDD + 0.7).
    Figure 16 of the bq77905 data sheet may be helpful. Between the enabled region and disabled region it is uncertain if the output will be enabled or disabled, avoid operation in this region.
  • 0 in reply to WM5295
    Intellectual 460 points
    Hi WM5295,

    Thank you for your detailed reply.

    Just to verify, when CTRC is disabled, the discharge fet continues to conduct and keeping discharging the battery?
  • 0 in reply to bar greidy
    TI__Guru 54715 points
    Yes, it will discharge through the charge FET body diode. If current is sufficient it will activate the body diode protection feature and the charge FET will be turned on again.
    To stop discharge current, use the CTRD input. If you want to stop both charge and discharge from the same signal, you could connect CTRC and CTRD inputs to the same signal.
  • 0 in reply to WM5295
    Intellectual 460 points
    Hi WM5295,

    Thank you for your quick reply!