LM5088: Output is not constant when there is no load.

Onur Keskin

Part Number: LM5088

Hi ,

I am develop an LM5088 application. Input voltage is 7-60Vdc. Output is 5V 5A. The problem is; When there is no load, output voltage continuously changes in 3-4V range. Also, I hear the coil voice.

I am using 8.2uH coil and double N-FET BSC123N08 . fw=275Khz. I saw suggestions about Cvcc and Cboot. I decreased/increased the capasitor values. There is a change, but when Vcc:1uF and Vboot: 100n with load,Vinmin=6V, when i make a change,Vinmin=7.3V with load.

What can i do?

over 7 years ago

0 Gautam Hari over 7 years ago

TI__Prodigy 360 points

Hello,

Can you please share your schematic?

Regards,
Gautam

0 Onur Keskin over 7 years ago in reply to Gautam Hari

Intellectual 390 points

Hi, BR.

0 Gautam Hari over 7 years ago in reply to Onur Keskin

TI__Prodigy 360 points

Just to confirm a few points:

1) The issue occurs only at low VIN? At higher VIN (VIN>9V) VOUT regulates accurately?

2) Increasing the VCC cap and decreasing the BOOT cap helped you at low VIN voltages?

If the above statements are accurate, what VIN level does VOUT start to move? How much improvement do you see when you increase the VCC cap?

Best regards,

Gautam

0 Onur Keskin over 7 years ago in reply to Gautam Hari

Intellectual 390 points

1-Yes. The issue occurs only at low Vin.
2-Partly helpful. But operating minimum voltage with load increased. (Ex. before Vinmin=~7,after Vinmin=~7.5).

When there is no load and Vinmin=~7.5-8, output voltage start to continuously changes.

BR.

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LM5088: Output is not constant when there is no load.