LM5145: Instability at higher Vout

Silvano Ghilardi

Part Number: LM5145

I'm using the LM5145 with an input voltage of 56V. I would like to go up to 52.5V with 14.4A. Everything works fine, but when I increase the voltage it looks like the regulator starts to be instable.

The maximum duty before it goes instable is depending of the load.

Is there any limitation that I don't know?

Thanks for the help.

Silvano

over 6 years ago

0 Timothy Hegarty over 6 years ago

TI__Guru 74212 points

Hi Silvano,

The capacitance of ceramics falls off with higher voltage - this may be leading to the instability. I recommend using the derated value of capacitance in the quickstart calculator to derive compensation components.

You can download this file from the product folder - please send the completed version for review. It would be good to also send the schematic.

Regards,

Tim

0 Silvano Ghilardi over 6 years ago

Intellectual 330 points

Hi Tim

Thanks for the fast answer. I increased the caps and now it looks stable. But still it has a strange behavior. It looks like that the duty is stable up to 94% and than again around 98%.

Can you explain that?

Silvano

0 Timothy Hegarty over 6 years ago in reply to Silvano Ghilardi

TI__Guru 74212 points

If it's stable at all other operating points, then it may be a noise effect. Send along the updated schematic and layout for review. Also, you should complete the quickstart calculator to check compensation and other component values. Here is the link: http://www.ti.com/tool/LM5145DESIGN-CALC

0 Silvano Ghilardi over 6 years ago in reply to Timothy Hegarty

Intellectual 330 points

Thanks for the answer. I have checked the caps and in the end I switched to Low ESR electrolytic capacitor and it is fine now.

I was able to stabile the circuit and to reduce the ripple.

Thanks

Silvano

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LM5145: Instability at higher Vout