LM5116: can we use our 12V aux rail to drive VIN, VCC, and VCCX ?

Jonathan Jank

Intellectual 1045 points

Part Number: LM5116
Other Parts Discussed in Thread: LM5576, LM76003

Hi,

We are using LM5116 to do:

Pwr Vin=60V Vout=24V Iout=3A

UVLO is set at ~30V

We have a 12V Aux rail that is available before the Pwr Vin is a available and we want to use this for our gate drive. What is the best way to connect this to the chip? The use cases later in the datasheet don't refer to this case.

One thought would be to tie it directly to VIN, VCC, VCCX pins, and then just allow UVLO to enable/disable the part, and wouldn't think a diode is needed since VCCX=VCC=VIN. We are not sure if this is allowed or not. We could also tie 12V to VIN, VCCX, and just put cap on VCC.

Let us know what is best ?

thanks,

over 4 years ago

0 Timothy Hegarty over 4 years ago

TI__Guru 73152 points

Hi Jonathan,

I'll check on this and get back to you. Note we have the LM76003 and LM5576 converters as options here for smaller solution size with integrated FETs.

Regards,

Tim

0 Timothy Hegarty over 4 years ago in reply to Timothy Hegarty

TI__Guru 73152 points

Hi Jonathan,

The main concern is that the VCC voltage should not exceed VIN, otherwise the reverse diode between these pins can conduct. One way around that is to place a diode in series with the VIN pin of the IC.

Note that it is preferable to connect the actual pwr input supply voltage (60V) to the controller as this results in correct line feedforward behavior and emulated current ramp slope (which depends on Vin - Vout during the on time).

Regards,

Tim