LM5146-Q1: LM5146-Q1: VCC generation issue

mahesh kohale

Part Number: LM5146-Q1

HI,

we are designing a BUCK converter using LM5146Q1- (Input range: 36Vdc to 72VDC and Output : 12Vdc )

we have problem of generating VCC- 7.5V when we applied VIN in range of 36V to 72VDC and our UVLO pin voltage is greater than 1.2V.

VCC is not generated from input voltage 36V to 65V once input voltage increase above 66V, it is generating 7.5V VCC.

we have not observed this issue in simulation.

Please look into this as we have stucked here.

Thanks and regards,

mahesh

over 5 years ago

0 Samuel Jaffe over 5 years ago

TI__Mastermind 25590 points

Mahesh,

Please attach a schematic and we will review.

-Sam

0 mahesh kohale over 5 years ago in reply to Samuel Jaffe

Prodigy 130 points

hi.

VCC issue has resolved with decoupling capacitor.

Now I am facing problem for IC heating at no load upto 115 degree C.

Do I need to connect VCC from output side as shown in datasheet diagram number 30.

we didn't observe this IC heating issue while doing simulations.

Mahesh

0 Samuel Jaffe over 5 years ago in reply to mahesh kohale

TI__Mastermind 25590 points

Mahesh,

You can implement the solution in Figure 30 to reduce the heat dissipation.

Please share an image of your layout. I will check if it's thermally optimized.

-Sam

0 mahesh kohale over 5 years ago in reply to Samuel Jaffe

Prodigy 130 points

Hi,

Please find attached PCB layout,

let me know is it OK.PCB.xlsx

0 Samuel Jaffe over 5 years ago in reply to mahesh kohale

TI__Mastermind 25590 points

Mahesh,

The layout can be modified to improve thermal performance. See the thermal layout guidelines in the datasheet. The GND plane connected to the thermal pad under the IC should connect to the GND plane on the board on the top layer. The current layout confines the heat to the plane directly under the IC. The vias help the heat escape to other layers but the top layer will be the best way to move the heat away from the IC.

It looks like you're driving two high-side FETs and two low-side FETs. You can use table 2 in the datasheet to calculate the expected power loss in the FETs from switching.

-Sam

Power management

Power management forum

LM5146-Q1: LM5146-Q1: VCC generation issue