BQ76942: Enabling FETs

Matthew Gardener

Part Number: BQ76942

I'm having trouble toggling the FET enable.

I modded the code under 2.9.1 in BQ769x2 Calibration and OTP Programming Guide to work with an aardvark and python.

Trying to enable the fets like this:

I2C_Write(I2C_ADDR, 0x3E, [0x22, 0x00])

sending the checksum and length:

I2C_Write(I2C_ADDR, 0x60,[0x22, 0x2])

Inside battery management studio sending 0x22 0x00 to 0x3E successfully toggles the output fets, but no luck in this script.

I am able to read cell voltages, and temperature. I suspect my issue is with the checksum and length, but I dont know what. I've tried a lot different combinations and adjusting the length.

over 2 years ago

0 Jose Couso over 2 years ago

TI__Mastermind 27321 points

Hello,

Have you looked at the BQ769x2 sample code? I will attach it here, but it is also in the product page.

sluc701a.zip

Here's a snippet of the sub-command writes of the sample code attached.

Regards,
Jose Couso

0 Matthew Gardener over 2 years ago in reply to Jose Couso

Prodigy 55 points

I tried modding the i2c write function with those bit operations but made no difference. I am also referencing the i2c write function here under 2.9.1:
BQ769x2 Calibration and OTP Programming Guide (Rev. A) (tij.co.jp)

Also this forum post references the checksum I was looking for help with:
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1051647/bq76942-write-fet_control-under-i2c

0 Jose Couso over 2 years ago in reply to Matthew Gardener

TI__Mastermind 27321 points

Hello Matthew,

The checksum is the sum of the subcommand and then take the NOT(of the sum) and the first two bytes is the checksum.

Although it is not required for FET_EN, please see below

W: 10 3E 22 00

W: 10 60 DD 04

DD is the inverse of the sum (22 + 00). 04 is the length of the bytes

Another example

Note: (to be able to write to RAM, the device must enter CONFIG_UPDATE mode)

Regards,
Jose Couso

0 Matthew Gardener over 2 years ago in reply to Jose Couso

Prodigy 55 points

Thank you for clarifying that I dont need to send the checksum.

I ended up using a beagle i2c analyzer and noticed all battery management studio was sending was 3E 22 00.

I was trying to use a register write function, but when I just wrote 3E 22 00 to the device it started working.

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BQ76942: Enabling FETs