LMS3655: Current delivery capability at particular operating conditions

David Cano30

Part Number: LMS3655
Other Parts Discussed in Thread: UCC27511,

Hello everyone,

I would like to know what is the maximum current that this converter could deliver when the input is 24 V and the output is 12 V.

According to Webench online tool, I have got the following results, but I want to be pretty sure about its capability:

Thank you for reading.

Best regards,

David.

over 5 years ago

0 Timothy Hegarty over 5 years ago

TI__Guru 59507 points

Hi David,

I forwarded your enquiry to the product expert. Can you share your schematic?

Regards,
Tim

0 David Cano30 over 5 years ago

Prodigy 210 points

* I meant: (...) when the input is 24 V and the output is set to 12 V.

0 David Cano30 over 5 years ago in reply to Timothy Hegarty

Prodigy 210 points

Hello Tim,

Thank you for your response. Of course I can.

Please, do not forget that Vin is a 24 V +- 10% battery, the output is 12 V. The buck converter is supposed to feed a TI UCC27511 MOSFET Driver, which requires a 4A peak current.

Driver_Vsupply.pdf

Thank you for your help.

I am looking forward to your reply.

Regards,

David

0 Timothy Hegarty over 5 years ago in reply to David Cano30

TI__Guru 59507 points

Hi David,

Note that the DC current requirement of the gate driver is much lower than 4A (the peak gate drive current pulse is short duration, ~20-40ns wide).

The average gate drive current is Qg*Fsw where Qg is the gate charge of the MOSFET at the applicable drive voltage level and Fsw is the switching frequency of the gate driver.

Regards,
Tim

0 David Cano30 over 5 years ago in reply to Timothy Hegarty

Prodigy 210 points

Hello Tim,

Thank you for answering. Yes, you are right. The average current value is not that high, but I want to charge the Mostef's Ciss as fast as possible (to reduce switching losses) and the amount of current that the driver should deliver to achieve that is around 4A peak (while Ciss is charging, once it is done, the current is minimal).

Now my questions are:

1) can the converter supply that amount of current?

2) now that you mentioned: is there a minimal output current value that the converter should deliver? if yes, would that mean that if the average current is not high enough, the converter could need a phantom load so that it works properly, right?

Thank you so much for your help.

Regards,

David.

0 David Cano30 over 5 years ago in reply to David Cano30

Prodigy 210 points

Hello Tim,
I still wait your answer.

Thank you for your help.

Regards,

David.

0 Ambreesh Tripathi over 5 years ago in reply to David Cano30

TI__Expert 6860 points

David ,

As Tim mentioned , what you need is a device which can support 300mA-500mA output current . THe peak drive capability is provided by the Capactior that is place on gate driver input .

Further LMS3655 shoudl be able to deliver 5A at 12V output .

---Ambreesh

Power management

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LMS3655: Current delivery capability at particular operating conditions