BQ25751: Schematic check

sun qiyun

Intellectual 280 points

Part Number: BQ25751
Other Parts Discussed in Thread: BQ25750, , BQ25820

Tool/software:

Dear

Could you please help check my schematic the buck-boost circuit?

In my design, I only use buck mode, using 30V power to charge 24V lead acid battery.

In the EVM, I think I can use diode to replace Q3 and Q6, is it right?

Could you please help explain how the circuit operate?

I use oscilloscope to test the FET drive signal. Why does Q8 also need to be driven? Thanks!

24 days ago

0 Christian Moyer 24 days ago

TI__Mastermind 32246 points

Hello Sun,

I recommend refering to our schematic checklist. You can use the BQ25750 checklist for BQ25751:https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1471662/faq-bq25751-schematic-checklist?tisearch=e2e-sitesearch&keymatch=BQ25751%20schematic%20checklist#

sun qiyun said:
In the EVM, I think I can use diode to replace Q3 and Q6, is it right?

This is not recommended.

Best Regards,

Christian

0 sun qiyun 23 days ago in reply to Christian Moyer

Intellectual 280 points

Thanks Moyer.

Could you please help explain in my design, I only use buck mode, why is Q8 also close in the charging process? It is for what?

0 Christian Moyer 23 days ago in reply to sun qiyun

TI__Mastermind 32246 points

Hello Sun,

sun qiyun said:
Could you please help explain in my design, I only use buck mode, why is Q8 also close in the charging process? It is for what?

The BQ25751 can not be used in buck-only mode, so you will still need all four of the switching FETS(Q2,Q3,Q6,Q8)

Best Regards,

Christian.

0 sun qiyun 22 days ago in reply to Christian Moyer

Intellectual 280 points

Hi, Moyer

I have a question about the BQ25751 EVM. The EVM reserves the D7, D8, R1002 and R1003, it is for what?

Please help explain.

Thanks!

+1 Christian Moyer 22 days ago in reply to sun qiyun

TI__Mastermind 32246 points

Hello Sun,

sun qiyun said:
I have a question about the BQ25751 EVM. The EVM reserves the D7, D8, R1002 and R1003, it is for what?

The BQ25751 is a spin of BQ25750, we also have another spin BQ25820( this is a buck only charger). We use the same PCB layout for each spin of the EVM.

So, for the buck-only charger (BQ25820). Q3/Q4 are not populated and R1002/R1003 are populated.

Q3/Q4 needs to be populated for BQ25751.

Best Regards,

Christian.

0 sun qiyun 21 days ago in reply to Christian Moyer

Intellectual 280 points

Thanks so much.

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BQ25751: Schematic check