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BQ24250C: High Resistance Between BAT input and VSYS output

Charles Wayman
Prodigy 10 points
Part Number: BQ24250C
Other Parts Discussed in Thread: BQ24250

Tool/software:

We have a BQ24250C that is being used as battery charger and PMIC on our system

What we are seeing is that periodically the VSYS voltage drops to <2VDC this condition lasts for ~100mS

In some cases, VSYS is not affected at all, in other cases we have the dropout in voltage

This state has been verified by monitoring the VBAT input with a scope at same time we monitor VSYS: VBAT is not affected, VSYS drops out:

Our system uses an external circuit to control the state of the EN2 signal.  The intent is to disable external DC power into the BQ24250C.

We note that the BQ24250C has a sleep mode: our suspicion is that the BQ is in sleep mode (With VBAT connected to VSYS via the internal FET) when we do not have a dropout. and that we are not in sleep mode when the issue occurs

Please advise what could be happening here

  • 0
    TI__Mastermind 31510 points

    Hi Charles, 

    Thank you for reaching out via E2E. We are working to investigate the reported behavior further. 

    Can you help to answer a couple questions.

    -To clarify you see the ~100ms drop on VSYS when it is being powered via battery? Or is it when SYS is being powered from IN (input supply)? 

    Charles Wayman said:
    We note that the BQ24250C has a sleep mode: our suspicion is that the BQ is in sleep mode (With VBAT connected to VSYS via the internal FET) when we do not have a dropout. and that we are not in sleep mode when the issue occurs

    Given this suspicion have you checked the status of fault register (REG00) for a sleep fault? If possible can you take a waveform showing Vin in addition to VSYS and VBAT?

    Best Regards,

    Garrett 

  • 0
    Prodigy 10 points

    We have determined that the BQ24250C is going open circuit on connection between BAT and VSYS lines in response to a short circuit detection on the VSYS voltage

    This condition happens when VSYS drops below a voltage at which short circuit is detected.

    We need to know the value of the VREF_MINSYS and VMENSYS voltages (Refer to functional block diagram on page 15 of the datasheet)

    What we see is that the BQ24250C opens the connection between VBAT and VSYS for 70mS at this time.

    On page 10 the recovery time from an output short is 64mS nominal (controlled by the internal fast RC oscillator in BQ24250C)  Since upper and lower limits are not stated and the spec on the internal clock has 3.0MHz +/-10% it is reasonable that the 70mS we observe is this output short circuit recovery time.

    We have successfully induced this the volltage dropout behavior by applying an uncharge 220uF capacitor to the VSYS output and seen the chip respond by creating an identical short circuit pulse.

    The one remaining pieces of information we need to resolve this issue are the voltages at which the BQ24250 detects short circuit on the SYS output

  • 0 in reply to Charles Wayman
    TI__Mastermind 31510 points

    Hi Charles, 

    Thank you for the detailed explanation of the current status of your debug. 

    Charles Wayman said:
    The one remaining pieces of information we need to resolve this issue are the voltages at which the BQ24250 detects short circuit on the SYS output

    The short circuit protection is triggered if VSYS drops 300mV below VBAT. 

    Best Regards,

    Garrett