BQ76920: Issue with BQ76920.

Vinith Nayaka

Part Number: BQ76920
Other Parts Discussed in Thread: BQ76200

Hi sir/mam,
I am using BQ7692006PWR in 3S configuration, I am having an issue with the BQ7692006. It's working fine for some cycles and suddenly the 3.3V of the BQ7692006 is gone. Because the 3.3V isn't available I wasn't able to communicate to the chip using I2C interface. I tried to give voltage greater than VBOOT on the TS1 line which generally invokes the chip to go from SHIP mode to NORMAL mode even then I wasn't getting 3.3V back. Can I know what must have gone wrong. Is there anything wrong on my design please verify, I am attaching my schematic here.
Any help would be appreciated, Thanks in advance.

Schematic

over 4 years ago

0 Matt Sunna over 4 years ago

TI__Guru* 81034 points

Hi Vinith,

Can you attach your schematic directly? I am not able to access shared drives like Google Drive from the TI network.

Thanks,

Matt

0 Vinith Nayaka over 4 years ago in reply to Matt Sunna

Intellectual 440 points

5280.Schematic_Battery_BQ76920_2021-01-12.pdf

This is the schematic corresponding to the above message sir. Please verify. Thanks in advance.

0 Matt Sunna over 4 years ago in reply to Vinith Nayaka

TI__Guru* 81034 points

I don't see anything that should break the part in this way. We do recommend a filter on the REGSRC pin (see Section 9 of https://www.ti.com/lit/an/slua749a/slua749a.pdf). We also recommend resistors between the BQ76200 DSG/CHG pins and the FET gates (see https://www.ti.com/lit/an/slua794/slua794.pdf).

TS1 needs a rising edge to boot the device. If this is not working, it may be that the device is damaged. The abs max voltage on REGSRC is 36V, so if there is a transient, it could be REGSRC is damaged. You can measure CAP1 to see if it is the expected voltage (3.3V).

Best regards,

Matt

0 Matt Sunna over 4 years ago in reply to Vinith Nayaka

TI__Guru* 81034 points

Hi Vinith,

I am not seeing anything obvious that would lead to the behavior you are seeing. We do recommend a filter on REGSRC rather than just a cap (see Section 9 of https://www.ti.com/lit/an/slua749a/slua749a.pdf) and we recommend resistors between the BQ76200 CHG/DSG pins and the FET gates (see https://www.ti.com/lit/an/slua794/slua794.pdf). The Abs max voltage for REGSRC is 36V, so if there is a large transient, it could damage the device. TS1 needs a rising edge to boot the device. If the device will not boot, it is likely REGSRC is damaged. You can also check the voltage on CAP1 to see if it measures 3.3V as expected.

Best regards,

Matt

0 Vinith Nayaka over 4 years ago in reply to Matt Sunna

Intellectual 440 points

Hi sir,
I am adding the resistances as you mentioned sir, Can I have the nominal values of the resistances at the specific points and also should I add the diode which is connecting the positive terminal of the pack to the BAT pin.

0 Matt Sunna over 4 years ago in reply to Vinith Nayaka

TI__Guru* 81034 points

I think around 1k should be a good value according to the BQ76200 document on driving multiple FETs.

Best regards,

Matt

0 Vinith Nayaka over 4 years ago in reply to Matt Sunna

Intellectual 440 points

Hi sir,
What about the diode that's present in the filter circuit for the BAT pin sir. Should I include it in my design.

0 Matt Sunna over 4 years ago in reply to Vinith Nayaka

TI__Guru* 81034 points

It is recommended - it will help prevent these pins from discharging too rapidly during a heavy load like a short-circuit event. REGSRC supplies the FET drivers, so this will ensure enough time for the FETs to turn off when the delay time for SCD is met.

Regards,

Matt

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BQ76920: Issue with BQ76920.