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BQ24780S: ACDRV question

Mon2
Prodigy 220 points
Part Number: BQ24780S

Hello. Please offer clarity on when ACDRV is enabled on the BQ24780s.

From the datasheet, the ACDRV is dependent on CMSRC. Yet CMSRC follows after the ACFET is enabled. Respectively, see this as a paradox on how can ACDRV be ACIN+6v for the gate of the ACFET when the ACFET is not yet ON ?

One thread on this forum mentioned that the REGN (6 volts) is used at the start of this enable cycle of ACDRV but again, if we have 19v on the input of the ACFET, we require 19+6v = ~25v on gate to enable this first fet.

VCC = 19v.

ACDET is > 2v4.

ACOK is typically pulled up to REGN.

What are we missing in our understanding ?

Also, is REGN a fixed ON LDO or will it turn OFF under some condition inside the BQ24780s ?

Thanks!

  • +1
    TI__Mastermind 33275 points

    ACDRV is dependent on if the adapter is present in the system or not. If the adapter is not present, ACDRV is pulled to CMSRC to keep ACFET and RBFET off. When ACDRV is pulled to CMSRC, the adapter is disconnected from the system. If the adapter is present and ACDET is above 2.4V and VCC is above SRN but below ACOV, then ACOK is HIGH, and ACDRV is 6V above CMSRC.

    REGN is a 6V linear regulator output supplied from VCC. LDO is ON when ACDET is above 0.6V, and VCC is above UVLO. A 2.2uF capacitor is needed to connect REGN to GND. REGN could be turned off during low power mode, with battery only.