BQ25750: Max current of embedded driver

Paolo Anterri

Part Number: BQ25750
Other Parts Discussed in Thread: BQ25756

Tool/software:

Hi everyone,

for a customer application I want to use the BQ25750. In this project I'll must to request an input current of 20A max and a input voltage that change from 5V to 60V . I'll wish to know up to how many mosfet in I can put in parallel, and which is the massimun output current of embedded driver.

For the H-bridge I want to use the BSC035N10NS5ATMA1 MOSFET, that have Qg max = 87nC.

Eventually, is it possible to use an external high/low side driver? And if it's yes, how I can connect it to BQ25750?

Thank you for your attention

Paolo A.

1 month ago

0 Ethan Galloway 1 month ago

TI__Genius 15920 points

Hello Paolo,

You can find the driver impedance in the datasheet:

The IC can't support an external driver, but you can provide an external gate drive of up to 12V. An external gate drive will help reduce the switching and conduction losses of the circuit.

What's your output voltage?

If you are using the BQ25750's power path switchover, the Δv should be less than 30V. You can read this FAQ page for more information: e2e.ti.com/.../faq-bq25750-what-do-i-need-to-know-about-the-bq25750-power-path-switchover

Best Regards,
Ethan Galloway

0 Paolo Anterri 1 month ago in reply to Ethan Galloway

Prodigy 20 points

Hi Ethan,

thank you for your quick reply!

In this project I do not use the direct power path control, so I use it for charge battery only.

The output voltage can change from 40V to 64V, depends from the battery pack connected.

The input voltage can also change from 5V to 60V.

For this reason I thought to use multiple MOSFETs connected in parallel, like in as in the following picture:

So my question is can I do this? The BQ25750 is able to drive this type of circuit.

Thank you.

Best Regards,

Paolo A.

0 Ethan Galloway 1 month ago in reply to Paolo Anterri

TI__Genius 15920 points

Hello Paolo,

Just for clarification, these are all switching FETs?

Keep in mind, we recommend that the capacitance on the switch node be C_SW(nF) < 160/VIN. I've copied the relevant part in the datasheet as well:

Best Regards,
Ethan Galloway

0 Paolo Anterri 1 month ago in reply to Ethan Galloway

Prodigy 20 points

Hi Ethan,

of course these are all switching mosFETs.

OK, but I did not found Csw in the mosfet's datasheet (BSC035N10NS5), how can I calculate it?

Best regards

Paolo A.

0 Ethan Galloway 1 month ago in reply to Paolo Anterri

TI__Genius 15920 points

Hello Paolo,

To calculate the Csw, you would start with the output charge, Coss, of the FET. You would then multiply the Coss by the amount of FETs on the switching node. I quickly calculated 4.6nF for Csw is too much for the charger.

I would recommend using no more than 2 FETs and using a large external gate drive.

Best Regards,
Ethan Galloway