LM5146-Q1: LM5146-Q1 Simulation with Vcc powered by Vout

Alex Teryohin

Part Number: LM5146-Q1

I'm trying to simulate the scenario (with PSpice), when the Vcc is powered by Vout or other external DC source (8V - 13V).

I've downloaded the "LM5146-Q1 PSpice Unencrypted Transient Model (Rev. A)"

The only thing I've added are two diodes in series to Vin and Vcc as mentioned by datasheet:

As you can notice the Vcc stays at 7.5V while 12V supply produces output power of -10.8KW!!!

I've also tried to connect Vout instead of 12V, so the output voltage is stuck at approximately 7.5V instead of getting 12V.

Am I missing something in theory of operation? Can it be some problem of the simulation model?

Thanks a lot

Alex

over 2 years ago

+1 Timothy Hegarty over 2 years ago

TI__Mastermind 49207 points

Hi Alex,

I suspect the model has a voltage source for VCC and may not be useful for external VCC connection.

I have a new version of the quickstart calculator file that has the option to calculate losses with external VCC. I can provide that later today.

Regards,

Tim

+1 Timothy Hegarty over 2 years ago in reply to Timothy Hegarty

TI__Mastermind 49207 points

Here is the quickstart file with option for external VCC:

LM(2)5145, LM5146 contorller design tool - revA3 -- 52Vin 5Vout 25A 300kHz.xlsm

0 Alex Teryohin over 2 years ago in reply to Timothy Hegarty

Prodigy 85 points

Hello Tim.

First of all, thanks a lot!

According to what you've wrote it is the PSpice model's limitation rather than simulation mistake.

One more question if possible: is there any advantage of using Vin as a source for Vcc instead of output voltage in case the output is 8 - 13V?

Sincerely,

Alex

+1 Timothy Hegarty over 2 years ago in reply to Alex Teryohin

TI__Mastermind 49207 points

Hi Alex,

As you know, VIN powers VCC through the internal LDO regulator if external VCC is not connected. When external VCC is connected, it removes the (VIN - VCC)*Icc power loss from the IC, especially when VIn is high.

Note also that the gate drive voltage will be higher than the nominal 7.5V, so the gate charge loss will increase. Also, the FET switches faster with a higher gate drive amplitude.

Regards,

Tim

0 Alex Teryohin over 2 years ago in reply to Timothy Hegarty

Prodigy 85 points

OK. I understand. Thanks a lot, Tim!

0 Timothy Hegarty over 2 years ago in reply to Alex Teryohin

TI__Mastermind 49207 points

Thanks, Alex.

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LM5146-Q1: LM5146-Q1 Simulation with Vcc powered by Vout