BQ76940: CHD and DSG operation in BQ76940

Preethi HN

Part Number: BQ76940
Other Parts Discussed in Thread: TIDA-00255

Tool/software:

Hi there,

I'm designing a BMS using TI IC BQ76940 but I'm failing to understand how DSG and CHG pins works in that. I used reference deign given by TI and with this design when load is connected to battery there is an voltage of 3.2 at DSG pin which should be driving MOSFET but MOSFET used in TI design has a Vth(thresh hold voltage) of 4.1V so 3.2V is not sufficient to drive MOSFET

I would like to know in what logic IC is detecting load and charger connections.

Thank you

1 month ago

0 Maxwell Verboncoeur 1 month ago

TI__Genius 17320 points

Hi Preethi,

Could you share the schematic?

The CHG and DSG pins might be overloaded if they are not properly driving high.

The load detection feature is described in Section 8.3.1.3.2 of the datasheet.

Regards,

Max Verboncoeur

0 Preethi HN 1 month ago in reply to Maxwell Verboncoeur

Prodigy 10 points

This the reference design I'm using from TIDA-00255 in this CHG and DSG are directly driving MOSFET AOB290L

And trying to drive this MOSFET from the output from this circuit pins CHG and DSG which is 3.2V

I did read Section 8.3.1.3.2 of the datasheet but I'm not clear on how SYS_CTRL1 register bit is reading the load

0 Maxwell Verboncoeur 1 month ago in reply to Preethi HN

TI__Genius 17320 points

Hi Preethi,

Is the device reporting an XREADY fault in the SYS_STAT register?

Also, do you have the section of the schematic showing how REGSRC and REGOUT are connected to the rest of the system?

Regards,

Max Verboncoeur

0 Preethi HN 1 month ago in reply to Maxwell Verboncoeur

Prodigy 10 points

This is the schematic where REGOUT and REGSRC are there

Regards

Preethi H N

0 Maxwell Verboncoeur 1 month ago in reply to Preethi HN

TI__Genius 17320 points

Hi Preethi,

Q1 is backwards. The source of the MOSFET should be connected to REGSRC and the drain should be connected to BAT. It looks like you have it the other way around. See Figure 9-3 of the datasheet for an example.

There is a chance that the AFE is damaged if the voltage at the pin exceeded 36V due to this connection.

Regards,

Max Verboncoeur

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BQ76940: CHD and DSG operation in BQ76940