BQ76952: Using Low-Side FETs : Charge FET driver component ratings

Ishan Panchal

Intellectual 640 points

Part Number: BQ76952

Hi There,

I am referring "Using Low-Side FETs " app-note(Figure 2-4) and I have some queries as listed below :

What should be the current ratings of Q3, D1 and D3 ? I am using " LM5111-1M/NOPB" gate driver having a current source capacity of 3A.
What should be the voltage ratings for these parts ? Should the ratings be more than 67.7VDC as per 16 cell configuration ?
What should be the V and I ratings for Q4 in16 cell configuration ?

Please let me know.

Thanks..!!!

over 3 years ago

0 Caleb Perez over 3 years ago

TI__Genius 11315 points

Hey Alex,

We're working on answering your question and will reply before the end of day tomorrow.

Thanks,
Caleb

0 Ishan Panchal over 3 years ago in reply to Caleb Perez

Intellectual 640 points

Hi Caleb,

Thanks, will be awaiting your response..!!!

0 Ishan Panchal over 3 years ago in reply to Ishan Panchal

Intellectual 640 points

Hi Caleb,

One more question, can I use a P-channel Mosfet instead of a transistor Q4 ?

Based on my research, I have selected components as shown in attached image.

Q36 and Q40 are P-channel mosfets rated at VDS = -20V and Id = -2A. Diodes are fast recovery with 1A current rating.

Please let me know your inputs on same.

Thanks..!!!

0 Caleb Perez over 3 years ago in reply to Ishan Panchal

TI__Genius 11315 points

Hey Alex,

Yes, those values should be okay for the diodes, you can reference figure 5-9 on the "using low side FETs" document to confirm. I'd recommend that rating on your MOSFETs be VDS = -40V. That is what the rating is for our design.

It is okay to use a P-channel MOSFET as Q4. This is stated in the paragraph above figure 2-4.

Thanks,
Caleb

0 Ishan Panchal over 3 years ago in reply to Caleb Perez

Intellectual 640 points

Hi Caleb,

May I ask why to use Mosfets with VDS = -40V ?

The gate driver will be providing no more than 12V at the output therefore I wanted to use mosfets with VDS = -20V.

Please let me know.

Regards,
Ishan

+1 Caleb Perez over 3 years ago in reply to Ishan Panchal

TI__Genius 11315 points

Hey Alex,

That was the VDS value of the MOSFETs that we used in our design. You should be fine with VDS = -20, however.

Thanks,
Caleb

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BQ76952: Using Low-Side FETs : Charge FET driver component ratings