LM5145: My LM5145 board doesn't work.

leng shen

Part Number: LM5145
Other Parts Discussed in Thread: CSD18563Q5A

Tool/software:

hi
I am working with LM5145 board.
But my LM5145 board doesn't work properly.
Input voltage is 48V and my design is 40V output.

But output is 0V and LM5145 IC is overheating.

Please review my schematic and help me.
Thank you.

4 months ago

0 Timothy Hegarty 4 months ago

TI__Guru 74162 points

Hi Leng,

Have you tried this design using the EVM?

Regards,

Tim

0 Timothy Hegarty 4 months ago in reply to Timothy Hegarty

TI__Guru 74162 points

Hi Leng,

The schematic looks okay, although the inductor at 3.3uH seems low, possibly giving high ripple current.

I recommend completing the quickstart calculator for this device and sending it for review as well. This is very useful to check component selection, review power losses, etc. Make sure to derate the ceramic Cout (i.e. a 10uF/50V capacitor is likely only 1-2uF effective capacitance at Vout = 40V).

https://www.ti.com/tool/LM5145DESIGN-CALC

Regards,

Tim

0 leng shen 4 months ago in reply to Timothy Hegarty

Prodigy 30 points

8228.LM5145_quickstart_calculator_A5.xlsm
Here is quickstart_calculator for my design.
Please review it.

0 Timothy Hegarty 4 months ago in reply to leng shen

TI__Guru 74162 points

75% ripple current is very high - try increasing the inductance for 30-40% ripple.

Also, make sure Cout is correctly derated for applied voltage, as this affects compensation.

30A is really high for the current limit if 12A is full load.

0 leng shen 4 months ago in reply to Timothy Hegarty

Prodigy 30 points

hi Timothy.

Thank you for your reply.
I would like to know the reason, the IC is overheating when input the 48V.

0 Timothy Hegarty 4 months ago in reply to leng shen

TI__Guru 74162 points

Can you measure the VIN pin current? The IC power loss is VIN times this current.

The current consumption should be the 2mA quiescent current plus the Qg*Fsw DC gate drive current contribution for each FET. The CSD18563Q5A FET is not very capacitive (Qg at Vgs = 7.5V is only 11.5nC).

0 leng shen 4 months ago in reply to Timothy Hegarty

Prodigy 30 points

When Power Up (48V), the power consumption of my board is 2.5W without any load.
And IC is overheating.
Internal Regulator can be reason of overheating? Internal Regulator is 48V to 7.5V.

0 leng shen 4 months ago in reply to leng shen

Prodigy 30 points

3187.PCB.PcbDoc Sheet.SchDoc

Here are my schematic and PCB in Altium designer.
I hope to solve the problem asap.
Please check my design and help me.
Thank you.

0 Timothy Hegarty 4 months ago in reply to leng shen

TI__Guru 74162 points

Okay I'll take a look and get back to you within a day.

0 leng shen 4 months ago in reply to Timothy Hegarty

Prodigy 30 points

hi Timothy.
Thank you for your effect.
Please share me your feedback after review my design.

0 Timothy Hegarty 3 months ago in reply to leng shen

TI__Guru 74162 points

Will do - apologies for the delay. I'll reply in the morning (US time).

0 Timothy Hegarty 3 months ago in reply to Timothy Hegarty

TI__Guru 74162 points

Have you tried increasing the inductance to reduce the ripple current? This is likely the main reason for the 2.5W no-load power loss.

0 Timothy Hegarty 3 months ago in reply to Timothy Hegarty

TI__Guru 74162 points

You can also measure the VIN current into the IC if you have a series resistor. The VIN (or VCC) current is mainly to drive the MOSFETs, where each MOSFET has a DC gate drive current to VCC of Qg*Fsw. However, the VCC current shouldn't be too high if Fsw is only 225kHz.

0 leng shen 3 months ago in reply to Timothy Hegarty

Prodigy 30 points

Thank you for your help.
I found the problem and fixed.
The output capacitors were problem. I added the output capacitors more and then I could fix the problem.
Thank you again.

0 Timothy Hegarty 3 months ago in reply to leng shen

TI__Guru 74162 points

Great, thank you.

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LM5145: My LM5145 board doesn't work.