BQ29312A alone

Finally, I made a board with the BQ29312A and a 32.768KHz oscillator powered with the REG pin. It works fine when trying to CHARGE, but it does not work when trying to DISCHARGE... It seems that the BQ29312A needs an I2C communication to enable the DISCHARGE path. But my MCU needs the DISCHARGE path to be enabled to work and to use the I2C...

So the BQ29312A needs the BQ20Z80 (TSSOP38 package) or similar or a dedicated MCU (consuming less than 24mA)...

Is there a small IC (and not the huge TSSOP24 + TSSOP38 !) that can cut the DISCHARGE path if the battery voltage is too low ?

Thank you.

Hi Jerome,

I would recommend reviewing the bq20z75 device.  It integrates the bq29330 analog front end with a bq20z70 TI gas gauge into the same plastic package.

The bq20z75 is a full featured battery fuel gauge allowing you to program many safety configurations including over-current during discharge.

Best regards, Keith

Hello,

Thank you for your recommendation. I wish I had it before I made my PCB...

The bq20z75 seems interesting, but the datasheet (SLUSA22 –DECEMBER 2009) seems quite light... for example :

- what happens if it detects the System (PRES pin) and if it does not detect it ?

- how does it enter to Shutdown Mode ?

- can the VCELL+ pin be used to measure the cells voltages, or the SMBus must be used ?

- where is the fuse in the schematic ? what happens if the PFIN pin is 0V ?

I may have not found the last datasheet.

Furthermore, is there an IC like the BQ29412 made for LiFePO4 cells (overvoltage around 3.6V) ?

Thank you.

Hello,

here are answers to your questions:

- what happens if it detects the System (PRES pin) and if it does not detect it ?

This functionality is described in the Technical Reference Manual.  This is a comprehensive document describing all functions in the gauge.  Specifically, the PRES pin is monitored if NR bit = 0.  Otherwise it is not monitored in Non-Removable configuration NR=1.

- how does it enter to Shutdown Mode ?

The gauge can enter shutdown mode by sending sleep command while the pack is unsealed.  The last step in production would be to seal the pack, unseal the pack, and issue sleep mode command.

- can the VCELL+ pin be used to measure the cells voltages, or the SMBus must be used ?

SMBus must be used.

- where is the fuse in the schematic ? what happens if the PFIN pin is 0V ?  I may have not found the last datasheet.

Please review the bq20z95 datasheet.  It includes the circuitry for the chemical fuse.  PFIN functionality would be covered in the Technical Reference Manual.

Furthermore, is there an IC like the BQ29412 made for LiFePO4 cells (overvoltage around 3.6V) ?

No, we do not have an IC with lower voltage protection.  My experience with LiFePO4 is the cell voltages can rise quickly near the end of charge above 4V.  Therefore an over-voltage protection in 4.2V range should not be an issue.

Hello,

Thank you for your help. Why should I review the bq20z95 datasheet if you recommended the bq20z75 ? And there is no Technical Reference for the bq20z75.

Thank you for the information. I understand better now.

If I don't want to use the fuse function, I can only pull-up the PFIN and let the SAFE opened ?

For information, on the bq20z75 page, there is : "Replaced by : BQ20Z75-180" and on the bq20z75-180 page there is no link to the Technical Reference.

The Technical Reference Manual applies to both versions of firmware (V160 and V180).

Check the settings for "PFIN Detect Time" for monitoring of PFIN pin.