LM5013: Efficiency

Christian Juhl

Part Number: LM5013

Hello

I'm designing this Buck converter with the LM. Input Source=37-57V, typically 52-53V. Output = 12V, 2A Load.

Switch Frequency is:262 KHz Aprrox

PCB Layout: (I followed the EVM module rules as much as possible)

Question:
Suggestions for raising the efficiency in order to get into the 90% area? Any components to try out?
At the moment efficiency is 80-86% depending on the load.
At 2A's, neither the diode, IC or inductor is getting hot. It is 30-35 degrees.
33uH inductor has 6A sat. current.

Is the 100uF ok on the output, C23?

Other value have been chosen through datasheet, EVM module, reading forums, and using the design tool.

9 months ago

0 Shipeng Cheng 9 months ago

TI__Expert 8710 points

Hi,

All power loss in the circuit will transfer into heat. So since devices are not hot, I don't think the efficiency is low. How do you measure the Vin, Iin, Vout and Iout?

BR,

Shipeng

0 Christian Juhl 9 months ago in reply to Shipeng Cheng

Prodigy 20 points

Hello
Well, inductor are in the 30-40 degree (22 ambient), so not cold, but not hot at all.
Current is measured with Fluke 89 at the fuse, voltage across input VDD and GND. Same goes for output/load.
Yesterday I came to the conclusion that the maximum 88% efficiency is kind of best case for me, 1A, 12V
The reason for creating this thread was to somehow, get closer to expected efficiency of +90%, with the 48-52Vin scenario.

0 Shipeng Cheng 9 months ago in reply to Christian Juhl

TI__Expert 8710 points

Hi,

Here are some steps to find why the efficiency is not high enough.

1. Could you measure the waveform of SW pin to see if the converter works stable?

2. And do you measure Vin on two terminals of C15 and measure Vout on two terminals of C20?

3. What is the DCR of your inductor L9?

Thanks.

BR,

Shipeng

0 Christian Juhl 9 months ago in reply to Shipeng Cheng

Prodigy 20 points

Hi

I will do this later.
1: What should I expect here - a constant switch frequency? A bit of overshoot/ringing?
2: Yes.
3: 64.4mR

0 Shipeng Cheng 9 months ago in reply to Christian Juhl

TI__Expert 8710 points

Hi,

it should be a constant switch frequency.

0 Christian Juhl 8 months ago in reply to Shipeng Cheng

Prodigy 20 points

This picture above is the switching pin with a light load (400mA).

With a bit heavier load (where I currently did a efficiency measurement) it looks like this:

0 Shipeng Cheng 8 months ago in reply to Christian Juhl

TI__Expert 8710 points

Hi,

The converter works normally. Maybe you can try to find a lower Vdrop diode.

Thank you.

0 Christian Juhl 8 months ago in reply to Shipeng Cheng

Prodigy 20 points

Ok, i will try this.

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LM5013: Efficiency