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Original question:

BQ76952: DFETOFF vs. body diode protection

BQ769142: Body Diode Protection vs FET control signals and commands

Enrico Benetti
Prodigy 40 points
Part Number: BQ769142

Tool/software:

Hi All,

can you confirm that CFETOFF, DFETOFF and FET control commands (CHG_PCHG_OFF, DSG_PDSG_OFF) override the body diode protection activation?

Using the I2C commands and driving the input signals (e.g. CFETOFF vs CHG_PCHG_OFF) has the same effetct or are there any difference (excepts for the timing for the request to takes effect)?

In other words, case (a):

1a. CFETOFF active

2a. SFET = 1

3a.Discharge current greater than DIODE_PROTECTION_THRESHOLD in magnitude.

lead to

4a. CHG + PCHG FETS status = OFF

Is sentence 4a correct or wrong?

Case (b), similar configuration:

1b. CHG_PCHG_OFF sent.

2b. SFET = 1

3b. Discharge current greater than DIODE_PROTECTION_THRESHOLD in magnitude.

lead to

4b. CHG + PCHG FETS status = OFF

Is sentence 4b correct or wrong?

Thanks for your support,

Enrico

  • 0
    TI__Expert 6810 points

    Hello Enrico,

    The CFETOFF and DFETOFF pins will disable the FETs and body diode protection will not work if disabled by these pins.

    There is a fast response for FET turn-off based on the enabled protection fault versus the FET turn-on based on a pin (e.g. CFETOFF). Table 6-9. Timing of Events in the BQ769142 Technical Reference Manual (TRM) will provide some more information there. 

    For your case statements, if by ‘CFETOFF active’ meaning that CFETOFF is asserted, the CHG FET and PCHG FET will be disabled. Even if the DSG current is greater than the diode protection threshold, the CHG and PCHG FET will remain OFF, unless CFETOFF is deasserted and there are no other items are blocking them from being reenabled. 

    The second statement should have the same effect as the first one. This is further discussed in Section 5.2.3.2 FET Control of the TRM. 

    Something to note, the subcommands 0x0093 DSG_PDSG_OFF() and 0x0094 CHG_PCHG_OFF() should not be used if the DDSG and DCHG pin are being used in DDSG and DCHG mode. This forum post should explain why it is not recommended. DDSG/DCHG Operation Further Explained

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 40 points

    Dear Alexis,

    thanks for your feedback

    From our initial tests it seems that the body diode protection works exactly as described by the TRM when the FETs are switched OFF through I2C commands. I.e. the FETs can be enabled if the current is greater (in magnitude) than the threshold.

    This is in contrast with your sentence "The second statement should have the same effect as the first one..."

    Can you please review my question, that is confirm if:

    - 4a is TRUE

    - 4b is FALSE

    In other words, can you confirm that

    a. Body Diode Protection DOES NOT WORK when disabling the paths via signals (CFETOFF/DFETOFF).

    b. Body Diode Protection WORKS when controlling the paths by the BQ device and HOST commands.

    Is there any document clearly stating this difference?

    Many thanks,

    Enrico

  • +1 in reply to Enrico Benetti
    TI__Expert 6810 points

    Hello Enrico,

    Thank you for catching that. I misread your second statement. 

    Enrico Benetti said:
    a. Body Diode Protection DOES NOT WORK when disabling the paths via signals (CFETOFF/DFETOFF).

    Correct.

    Enrico Benetti said:
    b. Body Diode Protection WORKS when controlling the paths by the BQ device and HOST commands.

    Correct.

    Other than what's stated in the TRM, unfortunately no. We may make a future FAQ document that helps clears this up.

    Best Regards,
    Alexis