BQ25756E: BQ25756E

Dante Fasano

Intellectual 260 points

Part Number: BQ25756E
Other Parts Discussed in Thread: LM74930, , TUSB320LAI, BQ25756, TPS25751

Tool/software:

Hello,

I am posting a couple of schematic pages that contain a BQ25756E along with a TUSB320LAI and a LM74930.

Can someone please perform a detailed review on any or all of the parts contained on these pages.

Best,

DanBRIDGE-SCHEMATIC-REV6-TI review-06-28-2024.pdf

6 months ago

0 Ethan Galloway 6 months ago

TI__Mastermind 21430 points

Hello Dan,

Here are my suggestions:

Make sure to have high frequency filter caps on the same nodes as C12 and C10. You can use a few 0.1µF ceramic caps for this. Put these caps close to Q4 and Q5.

Install an RC filter on the ILIM_HIZ and ICHG resistors. We recommend this when those resistors are greater than 5kΩ. You can check the RC filters than are on the EVM.

Make sure C24 and C25 are close to pin 32 and pin 33 in the layout. I also recommend just using a PCB trace to connect pin 32 and pin 33 together.

It seems like the he L1 inductor is way overkill for your application. It will work, but you could get a cheaper inductor.

For your FETs, I would recommend getting FETs with a lower threshold voltage. The FETs currently have a threshold voltage of 2.6V to 3.6V. The BQ25756E EVM comes with the AONS66614 which has a threshold voltage of 1.2V to 2.4V

If you are going to be doing USB source contracts with the BQ25756E, I would recommend a 5mΩ input current sense resistor.

If your battery termination current is less that 2A, I recommend setting EN_PFM=0. This will improve the termination accuracy.

Here's the BQ25756 schematic and layout checklist for reference: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1277772/faq-bq25756-schematic-and-layout-checklist

Let me know if you have any questions.

Best Regards,
Ethan Galloway

0 Dante Fasano 6 months ago in reply to Ethan Galloway

Intellectual 260 points

1) I added .1uF caps near C12 and C10

2) I add the filter for ILIM_HIZ and ICHG

3) I changed the connection between pin 32 and pin 33 to be like the eval board

4) I changed the 10uH to IHLP4040DZER100M8A, check it out

5) I needed the higher Vds for the FETs for our application (surge protection), do you think the threshold is a problem?

6) For the 5mohm you mentioned do you mean in place of R38? Can you explain why?

7) ok on the EN_PFM setting, that's a register bit I presume?

8) I will go over the checklist.

Thanks,

0 Dante Fasano 6 months ago in reply to Dante Fasano

Intellectual 260 points

Please answer ASAP

0 Ethan Galloway 6 months ago in reply to Dante Fasano

TI__Mastermind 21430 points

Hello Dan,

4. This inductor should work.

5. The higher threshold voltage is potentially a problem. Could you use a FET like the SiR680LDP or the SiR880BDP?

6. I was thinking about the TPS25751 when I wrote this. Check with the TUSB320LAI team if you need to change R38.

7. Yes, EN_PFM is a register bit.

Best Regards,
Ethan Galloway

0 Dante Fasano 6 months ago in reply to Ethan Galloway

Intellectual 260 points

5) I guess I don't understand why since there is a big charge pump on the chip and the Vgs gets pretty high?

0 Dante Fasano 6 months ago in reply to Dante Fasano

Intellectual 260 points

Also, I am going to change to the non-E part if that makes a difference for anything we have been discussing

0 Ethan Galloway 6 months ago in reply to Dante Fasano

TI__Mastermind 21430 points

Hello Dan,

5. The charge pump in the chip only works when either the buck or boost side is at a 100% duty cycle.

Changing to the non-E part will not make a difference.

Best Regards,
Ethan Galloway

0 Dante Fasano 6 months ago in reply to Ethan Galloway

Intellectual 260 points

Ethan - here is the schematic as it now stands. Please give it one more final look over before I commit to PCB payout.

Thanks,

DanBRIDGE-SCHEMATIC-REV6-TI review-07-03-2024.pdf

0 Ethan Galloway 6 months ago in reply to Dante Fasano

TI__Mastermind 21430 points

Hello Dan,

The schematic looks good, but if the charger is doing USB sourcing or sinking, the input sense resistor should be 5mΩ or higher. A 5mΩ sense resistor is more accurate and better suited for USB contracts than a 2mΩ input sense resistor.

Best Regards,
Ethan Galloway

0 Dante Fasano 6 months ago in reply to Ethan Galloway

Intellectual 260 points

Ok, I will change the input sense to 5mohm

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BQ25756E: BQ25756E