L6984 produce wrong voltage

[SSchm.5]

Hello everybody,

I need a power conversion DC-DC 24V to 3.3V. So I went to eDesign suite who recommendend me the following architecture:

I reproduced it in my design:

 

I produced the board, and when I apply 24V on the input, I obtain only 0.9/1V on the output.

Someone have an idea why?

Taking in account that I had to use a different inductor from the one recommended (same inductance, lower Isat). And there is another DC/DC converter after this one, supposed to convert 3.3V to 3.0V.

Thank you.

[Patrizia BELLITTO · Accepted solution]

Hello,

sorry but thank you to your reporting we found an issue in the schematic. In this configuration, pin FB must be connected to VCC. Can you try and let us know if it works?

Meanwhile we are fixing the schematic.

Thanks again,

Patrizia

[SSchm.5]

Hello,

Do you mean FB must be connected to Vout AND VCC or only to VCC?

[Patrizia BELLITTO]

Connect FB to the VCC pin and VBIAS to the regulated output voltage (see Figure 1 on page 1 in the datasheet)

[SSchm.5]

I did the modification on the prototype and now I get the 3.3V I need.

Thank you,