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bq40z60 VCC and AC FETpin

Sunil Panchal
Prodigy 30 points
Other Parts Discussed in Thread: BQ40Z60

According to the bq40z60 datasheet's  following quoted text, I have a question. 

"The AC FET (N-CH MOSFET) controls power input from the AC adaptor to the battery charging system by monitoring the voltage at the VCC pin, and turning ON the ACFET if the voltage exceeds the VHSRN voltage. The following register command sets the AC FET gate drive output control, AFE_STATUS register (0x01) ACFET (Pin 2): Setting this pin to 1 allows the AC FET gate drive to be on if other conditions are satisfied."

Refer Fig. 2, on page 23 of SLUSAW3C (bq40z60 datasheet) document and reply below questions. 

1. How VCC pin is going to get voltage when ACFET is off?

2. Who is going to control ACFET MOSFET? I mean how ACFET MOSFET shall get ON/OFF? Who makes it ON/OFF? 

3. Why do we need ACFET MOSFET? Is it necessary to have it? If no, provide reference circuit without ACFET MOSFET. 

 Look forward for reply.

  • 0
    TI__Guru 73830 points
    Sunil
    The SCFET shown in the figure in the datasheet is not configured properly. Please refer to the schematic in the EVM User's Guide. The cathode of FET body diode points towards the charger and will allow current to pass when the FET is off. The purpose of the ACFET is to prevent current flow in the event that VACP is lower voltage than VSYS. The gauge will control the ACFET for protection. You can remove the ACFET and leave the ACFET pin on the device open.
    Tom