LM5170-Q1: LM5170-Q1: External gate driver(UCC27712DR)

user5339996

Prodigy 80 points

Part Number: LM5170-Q1
Other Parts Discussed in Thread: LM5170, UCC27712

Dear experts,

Because my input voltage maybe exceed over 100V, I want to use gate driver UCC27712DR to drive MOSFET.

my schemetic is like the attached file.

But I can't find low side start to charge C968.

If I delete R921, I can't find LO2 to GND switching either.

Can you help me about how to add UCC27712DR gate driver to use in LM5170?

Thank you.

Steven

over 4 years ago

0 Youhao Xi over 4 years ago

TI__Guru* 78725 points

Hi Steven,

Thank you for posting. You may try the concept of the following drawing to help you to pre-charge the UCC driver's boot capacitor.

Driver Connection Simple.vsd

Thanks,

Youhao

+1 Youhao Xi over 4 years ago in reply to Youhao Xi

TI__Guru* 78725 points

Driver Connection Simple.pdf

Just realized you may not be able to open the .vsd file. A pdf version is attached.

0 user5339996 over 4 years ago in reply to Youhao Xi

Prodigy 80 points

Dear Youhao

Thank you for your reply.

I also have a problem with VIN pin.

Can I use resistor+zenor or another method to avoid Vin pin over 100V?

It's a short test item to exceed over 100V (about120V), not normal condition.

Thank you.

0 Youhao Xi over 4 years ago in reply to user5339996

TI__Guru* 78725 points

Yes you can.

0 user5339996 over 4 years ago in reply to Youhao Xi

Prodigy 80 points

Dear Youhao

I try to use your suggestion, then I found some problem:

1. My capacitance with HB to SW doesn't charge over 7V, and external driver(UCC27712) bootstrap capacitance is only 3~5V.

I try to change schematic like below, but the main problem is also the voltage with HB to SW in LM5170.

Can my schematic work or I need to change to your suggestion ?

Please help me how I can charge my cap and the schematic can work.

Thank you.

Steven

0 Youhao Xi over 4 years ago in reply to user5339996

TI__Guru* 78725 points

Hi Steven,

You need to increase the resistor (499 initially) or the capacitor (100nF initially) to extend the precharging for longer times. Once HO is exceeding its UV threshold, the precharging pulses will stop because the LM5170 considered the establishment of adequate boot voltage. Delaying HO voltage will allow more precharging cycles to get your external driver boot capacitor fully charged.

Thanks,

Youhao

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LM5170-Q1: LM5170-Q1: External gate driver(UCC27712DR)