Charge and Discharge lines high enough to turn on FETs?

Neil Ragsdale

Prodigy 165 points

As follows:

1) I'm using a design that charges 4 Lithium Ion batteries to 16V.

2) From the datasheet the maximum voltage from the charge and discharge lines on the gas gauge chip is 16V...

Question: How does the BQ20Z95 turn those N-channel FETs on?

Note: I'm using the reference design in the BQ20Z95 datasheet.

over 14 years ago

0 Jackie Hui over 14 years ago

TI__Expert 3865 points

The output voltage on CHG and DSG pin is from 8-16V. This is controlled by an internal FET driver circuitry. When you design a circuit, you should pick a FET with Vgs on lower than the CHG/DSG voltage output range.

0 Neil Ragsdale over 14 years ago in reply to Jackie Hui

Prodigy 165 points

So with a design that has 4 Lithium Ion cells in series the FDS6690A N-FET in the reference design is not the part to use?

With that N-FET configuration don't I have to bias above the battery/charging voltage by some amount to turn them on?

0 Ryan Manack over 14 years ago in reply to Neil Ragsdale

TI__Intellectual 2610 points

The CHG and DSG voltage output that is spec'd on page 7 of the datasheet is in relation to the source voltage on each of the MOSFETs. The bq20z95 will drive the CHG and DSG pins between 8 and 16V above the source voltage of each FET when activated. The abs max for these CHG and DSG pins is listed on page 4 and is 34V.

Power management

Power management forum

Charge and Discharge lines high enough to turn on FETs?