BQ76952: BQ76952 BMS IC loosing SPI comms after uploading configuration parameters

Hello Lain,

When you open BQStudio, what protocol gets automatically detected? Communication might be lost if the wrong protocol it's been detected.

Instead of power cycling the device, restart BQStudio. Power Cycling the device resets the custom configuration.

Regards,
Jose Couso

Hi Jose,

SPI gets detected automatically and we are able to read back register data via SPI initially. The problem seems to be that the SPI comms always falls over when we try to upload a configuration file via SPI. Comms appears to start and then the comms is lost…

thanks, Iain

Hello Iain,

I was talking to my team about this as this seemed an odd case. Turns out the BQ76952-01 device version has the REG1 off by default. Try connecting 3.3V to REG1 directly (the MISO signal uses REG1).


If using our EVM, see below.

To verify that the device works properly in SPI with CRC mode:

1. Turn the power supply off
2. Set J30 and J33 to the lower position for SPI
3. Install J27 (left position) for SPI. Install J24 (SPI_CLK).
4. Connect a wire from TP18 (3.3V) to the REG1 signal on J18 (top of board). This will allow the 1.8V SPI output to level translate to the 3.3V MSP430 on the board.
5. Restart BQStudio. It should now recognize the device and communicate with SPICRC mode.

Hopefully this will fix the issue.

Regards,
Jose Couso

Hi Jose, thanks for your help here. I just double checked our schematics and it is actually the BQ7695203 version we have. Apologies, I gave you the wrong variant number. This -03 version defaults to SPI mode with REG1 on (+5V). Here are the schematics of our design around the REG1 LDO and SPI interface.

Hello Iain,

Please share your configurations.

Regards,
Jose Couso

Hi Jose, is there an email address I can use to get these to you?

Hello lain,

You can directly send the configuration file to Jose's private messages here in e2e.

It is the beginning of the weekend, so expect a response by Monday end-of-day at the latest.

Best Regards,

Luis Hernandez Salomon

Thanks Luis, I just sent it to Jose.

Hi Jose, I just sent the configuration file. We have been working further on this and there is a chance that the battery pack we are using was at a very low SoC. The working theory is that the pack voltage was sufficient to maintain comms when we first connect to BQ Studio but when we try to upload the  configuration file, there may result in additional current draw due either to register updates or maybe features we enable which cause the pack voltage to collapse. 

We have charged the pack again and we don't experience a problem now. I am going to monitor the pack current in the future when we program the config file to see if there is an increase (even transiently) as it would be good to be sure we have found the issue. If you see anything strange in our config file then please do let me know.

Thanks for your help,

Iain

Hello Iain,

By looking at your configurations, the only thing I could think that will cause loose communications is the shutdown stack voltage and shutdown cell voltage. When you said the battery pack was a very low SoC, what was the reading voltage? If the battery pack voltage is less than Power: Shutdown: Shutdown Stack Voltage, then the device will enter shutdown mode after uploading the custom gg file. Causing it to restart the device, and the default configurations will upload again. To avoid this, ensure the battery pack voltage is higher than this parameter setting.

Also, just to confirm. What is the reading voltage of REGIN pin when the battery stack voltage is low? It must read about 5.5V to ensure the REG1 LDO output is 3.3V as per your configurations.

Regards,
Jose Couso