BQ76972: Unused pin and MOSFET driving resistor value

Minki Li

Prodigy 65 points

Part Number: BQ76972

Tool/software:

Hi:

How can i do with those pin are not using in final design?(No any external circuit need supply voltage)

1.REG2

2.REG1

3.REGIN

4.BREG

Can i just ground it of need a 100nF cap to ground for best EMC?

And like:

FUSE,DCHG,DFETOFFF,CFETOFF,HDQ,TSX

Will have EMC problem if that float?

I find there had 2 5.1K resistor in there,why need 2 5.1K?If i using multi FET can i reduce the value and using 1 resistor only?(Now is 12 fet with 51R on each gate)

And i see D11 is not using but i see it suggest on other datasheet,what is the using of this and should i keep it?

Thank You

over 1 year ago

0 Thomas Rainey over 1 year ago

TI__Expert 4320 points

Hello,

1. REG1- Leave floating or connect to pin 17 (VSS)

2. REG2- Leave floating or connect to pin 17 (VSS)

3. REGIN- Connect to pin 17 (VSS)

4. BREG- Connect to pin 17 (VSS)

You can refer to Table 8-3. Terminating Unused Pins of BQ76972 3-Series to 16-Series High Accuracy Battery Monitor and Protector for Li-Ion, Li-Polymer, and LiFePO4Battery Packs datasheet for more information on terminating unused pins.

Floating the pins that are meant to be left floating will not cause EMC issues.

The two 5.1kΩ resistors are used to help divide the power dissipation.

The D11 zener diode works as a voltage clamp to protect the DSG pin.

0 Minki Li over 1 year ago in reply to Thomas Rainey

Prodigy 65 points

Thank You

>The two 5.1kΩ resistors are used to help divide the power dissipation.

How to choosing the value of R76,78?

And what if i want the FET turn off more quickly change R77 to a low value?

Like 100R even 51R?

Thank You

0 Thomas Rainey over 1 year ago in reply to Minki Li

TI__Expert 4320 points

Hello,

For choosing values of R76 and R78 it would be best to go with the values provided. However, if you test the device with other values and find that they work, that is okay too.

You can refer to BQ769x2 Frequently Asked Questions section 2.7 How can I achieve faster gate turn-offs for DSG? for information on how to increase turn of speed of DSG.

Best regards,

Thomas Rainey

Power management

Power management forum

BQ76972: Unused pin and MOSFET driving resistor value