BQ77915: Load Turning Off

Mark Philip Felipe

Part Number: BQ77915

Hi Team, We would like to seek your support in this matter. There is a design 3s2p BMS with bq77915. The circuit is working initially however at some point it would off load.

We would like to seek your support to validate the schematic. Please let me know to whom can I send it.

Thank you very much.

Regards,

- Mark

over 4 years ago

0 David Hien over 4 years ago

TI__Genius 10830 points

hi Mark Philip,
I sent you an email on this topic.

0 Mark Philip Felipe over 4 years ago in reply to David Hien

TI__Genius 10820 points

Hi David,

According to our customer

The resistor is added as suggested and still we are having same observation. Load turning off after 5 to 6 secs.

Thank you.

-Mark

0 Matt Sunna over 4 years ago in reply to Mark Philip Felipe

TI__Guru* 81034 points

Hi Mark,

Can you get some more details on the behavior from the customer? When they say the load is turning off, does this mean the DSG FET is switching off? Or both the CHG and DSG FETs? There are multiple protections that can trigger the FETs to switch off. Tables 9-5 and 9-1 in the datasheet are very helpful for diagnosing which protection is triggering. The temperature protections all have a 4.5 second delay - do they have a thermistor correctly connected on the board?

Best regards,

Matt

0 Mark Philip Felipe over 4 years ago in reply to Matt Sunna

TI__Genius 10820 points

Hi Matt,

According to them, Both FETs are switching OFF. And all the possible triggers for protection are verified and everything is working fine except the voltage across Rsns as specified before. Even the thermistor is rightly connected, although the behavior is same when the thermistor is disconnected from the board.

Thank you.

-Mark

0 Matt Sunna over 4 years ago in reply to Mark Philip Felipe

TI__Guru* 81034 points

Hi Mark,

When the thermistor is disconnected from the board, are they connecting a 10k resistor from the TS pin to VSS? This is important, otherwise it will definitely trigger a temperature fault.

Matt

0 Mark Philip Felipe over 4 years ago in reply to Matt Sunna

TI__Genius 10820 points

Hi Matt, based on the feedback of our customer, they do place a 10k resistor when the thermistor is disconnected. Are there other considerations?

Thank you in advnace.

0 Matt Sunna over 4 years ago in reply to Mark Philip Felipe

TI__Guru* 81034 points

Hi Mark,

I cannot see any other reason the FETs would turn off from the schematic you sent. Do any components appear to be damaged on the board? If they disconnect and reconnect the cells, does the device recover? It would be good to verify that the FETs are being switched off by the device (due to protection triggering) vs. being switched off due to the IC or other component damage.

Best regards,

Matt

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BQ77915: Load Turning Off