BQ76920: not communicating via I2C

Scott Nelson

Part Number: BQ76920

I'm just getting started with the BQ76920 for monitoring 4 cells. I'm using the "Typical Application" schematic from page 47 of the datasheet but getting no response over I2C. What's the most minimal circuit I can use to troubleshoot this? I know I have the I2C configured properly on my microcontroller since I can communicate with other I2C slaves.

Thanks!

-Scott

over 8 years ago

0 Vish Nadarajah over 8 years ago

TI__Expert 6085 points

Since the controller can talk to other devices, the typical issue in I2C communication is the actual device addressed itself. Depending on the version of the bq76920 device being used, check if the address is 0x08 or 0x18. The address given on pp#4 of d/s

0 Scott Nelson over 8 years ago in reply to Vish Nadarajah

Intellectual 340 points

I do not get a response from either address. I'm using a BQ7692000PWR which looks like it should be available at 0x08.

0 Vish Nadarajah over 8 years ago in reply to Scott Nelson

TI__Expert 6085 points

I2C is pull-low type bus; it should be terminated with the pull-ups; without pull-ups the part will have floating inputs.

0 Scott Nelson over 8 years ago in reply to Vish Nadarajah

Intellectual 340 points

SDA and SCL are pulled up to 3.3V

0 Vish Nadarajah over 8 years ago in reply to Scott Nelson

TI__Expert 6085 points

If SDA is LOW, please send 9 clocks from the Host to clear the BUS.

0 Scott Nelson over 8 years ago in reply to Vish Nadarajah

Intellectual 340 points

I tried pulling SDA low for 9 clock cycles and then let SDA back up. I then followed that by attempting to address 0x08 but got no ACK. Here's a screen capture from my scope showing the addressing: http://imgur.com/a/bSfHD

0 Scott Nelson over 8 years ago in reply to Vish Nadarajah

Intellectual 340 points

Any other suggestions?

0 Vish Nadarajah over 8 years ago in reply to Scott Nelson

TI__Expert 6085 points

Scott,

there are no known failure mechanism for malfunction. In general if a SLAVE device holding the SDA line LOW, the host sending an extra clock (9) releases the bus.

Unless the bus is experiencing severe transients and the IC needs a power to be removed. can you insert a zener clamps @ 3.6V on SDA and SCLK. Not heard of this IC latching up, but the bus clearing scheme tends to help many of the customers application. the bq769x0 does not offer a RESET pin.

0 Scott Nelson over 8 years ago in reply to Vish Nadarajah

Intellectual 340 points

I'm not sure what the issue was but I soldered on a new BQ76920 and I can now communicate with it.

0 Vish Nadarajah over 8 years ago in reply to Scott Nelson

TI__Expert 6085 points

good disposition. good luck.

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BQ76920: not communicating via I2C