LM3691TL-1.8EV: Spurious signals at 60kHz

Adam Daluga

Part Number: LM3691TL-1.8EV

Hi,

We are using both the LM3691TL-1.0 & LM3691-1.8, we noticed spurious signal coming out the these regulators around 60KHz with harmonics, varies with temperature, is there a clock internal to the chip running at this rate?

Thanks,

Adam

over 2 years ago

0 Varun John over 2 years ago

TI__Genius 16340 points

Hi Adam,

The internal clock should be running at around 4MHz - the PWM switching frequency. The converter could be in ECO mode in the application, where it can switch at even 60KHz for a certain load current. Can you monitor the SW node to see if it is switching at 60KHz? If you find that is true, you can either set the MODE pin high to make it go into forced PWM operation or increase the load current to increase the switching frequency.

Best regards,

Varun

0 Varun John over 2 years ago in reply to Varun John

TI__Genius 16340 points

Hi Adam,

Were you able to check if the converter was switching at 60kHz?

Best regards,

Varun

0 Adam Daluga over 2 years ago in reply to Varun John

TI__Expert 5920 points

Hi Varun,

We looked at the switching frequency, it was at ~4MHz, the ~60KHz was a low level spurious measured with a spectrum analyzer, in most instances it would not be an issue, we did place an LC filter to reduce it and it eliminated the issue it was causing.

Thanks,
Adam

0 Stefano Panaro over 2 years ago in reply to Adam Daluga

TI__Expert 7595 points

HI Adam,

Please allow me to jump in since Varun is out of office.

Thanks a lot for the update.

Let us know if there is anything else that you need form our side.

Thanks,

Stefano

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LM3691TL-1.8EV: Spurious signals at 60kHz