BQ77915: Schematic design review

Samo Smodiš

Intellectual 362 points

Part Number: BQ77915

Hello,

I would be greateful if I could get a schematic design review for my circuit based around BQ7791500 IC.

The requirements for the circuit were:

- 5S Li-ion cells

- 80A discharge current nominal

- 10A charge current nominal

I have designed separate discharge and charge current paths due to high difference between the discharge and charge currents, and to get lower losses during discharge. Do you see any possibilities of unwanted circuit behaviour because of this?

Thanks!

Samo Smodiš

231124 SCH.pdf

over 2 years ago

+1 Andria McIntyre over 2 years ago

TI__Expert 8526 points

Hi Samo,

Comments and recommendations can be seen below:

It looks as though the PACK- line will also be the CHG- line. If you are planning to connect the charger across CHG+ and PACK-, then placing the CHG FET in series with the DSG FET in a typical configuration should also be able to control the flow of charging current as intended. This may be worth considering.
Double check with the Device Comparison Table to ensure the sense resistor you have selected will trigger protections based on the factory-programmed threshold values, especially since the nominal current is so high.
Ensure that no more than 50mA is flowing through the internal cell balancing FETs.
Connect VDD to BAT+, not PACK+
VC1 capacitor should be connected to GND.
The device variation selected requires load detect removal. Please see section 10.1.1.4 in the datasheet for more information on configuration.

Best,

Andria

0 Samo Smodiš over 2 years ago in reply to Andria McIntyre

Intellectual 362 points

Hi Andria,

Thank you for the suggestions. The separate discharge and charge paths are designed according to this article from TI "High Side P-channel Charge FET with the bq779x5 Battery Protector"

https://www.ti.com/lit/an/slua910/slua910.pdf?ts=1700057968087&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ77915%253FkeyMatch%253DBQ77915%2526tisearch%253Dsearch-everything%2526usecase%253DGPN-ALT

Regards,

Samo

0 Samo Smodiš over 2 years ago in reply to Samo Smodiš

Intellectual 362 points

One more question - where should the GND of the IC connect with the BAT- potential? Should it be made over the sense wire which senses the cell0- voltage, or should it be done next to the current shunt?

0 Andria McIntyre over 2 years ago in reply to Samo Smodiš

TI__Expert 8526 points

Hi Samo,

The GND should be at BAT-, not on the PACK- side of the sense resistor. You can simply use a net tie between GND and BAT- for naming conventions in your schematic design software.

You can use the app note mentioned previously (bq77905 Separate Current Paths (Rev. A) (ti.com)) as reference.

Best,

Andria

Power management

Power management forum

BQ77915: Schematic design review