BQ77915: BQ7791506 - VTB not present

Dave Mellick

Part Number: BQ77915

We are working with a 4 cell LiPo battery pack and are using the BQ7791506 chip. The chip appears to be working correctly with the exception that there isn't any VTB present. We've tried multiple chips and different boards. In all cases DSG and CHG are high so it does not appear to be in any fault state. What would cause the VTB to not be outputting anything? We need to ensure that the temperature protections for the pack are enabled. Attached is our schematic. 2843.Schematic Prints.PDF

over 5 years ago

0 Shawn Hinkle over 5 years ago

TI__Expert 7465 points

Hi Dave,

I checked your schematic, and couldn't seem to find any issue. Have you tried simulating the overtemperature or undertemperature condition and observing the fault? I would also suggest trying a new thermistor if possible, we recommend this one: https://www.mouser.com/datasheet/2/362/semitec_atthermistor-1202913.pdf.

0 Dave Mellick over 5 years ago in reply to Shawn Hinkle

Prodigy 50 points

Hi Shawn,

We've built several of these boards now and they all have the same output. I haven't tried simulating the temperature faults because there isn't any bias voltage on VTB so then the voltage at TS is always 0V. The thermistor we are using is a 10k ERT-J1VG103FA. I've tested their response and they are fine.

The data sheet schematic of the internal workings of the chip shows that VTB output can be enabled and disabled but there isn't any mention of what those parameters are. What would cause VTB to output 0V always?

0 Shawn Hinkle over 5 years ago in reply to Dave Mellick

TI__Expert 7465 points

Hi Dave,

The voltage on the VTB pin is not constant, it is a sequence of very quick pulses. So it may be hard to measure. I would suggest forcing the device into a temperature fault to make sure it is working correctly.

0 Dave Mellick over 5 years ago in reply to Shawn Hinkle

Prodigy 50 points

Thanks. That did answer my question. I don't see any mention of that though in the datasheet so you might want to make note of that in the future.

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BQ77915: BQ7791506 - VTB not present