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LMR38020: Incorrect switching frequency

Pjs

Intellectual 890 points

Part Number: LMR38020

Tool/software:

Hi,

We are using the LMR38020FSDDAR (fixed PWM, spread spectrum variant) to step a rail down from 24V to 5V. We are using the RT_SYNC pin with an external resistor 52.3kR to set the switching frequency to 500kHz. However, when measuring the ripple, we can see that the regulator is operating at 2MHz. This is happening with multiple boards and we're unsure why the switching frequency is wrong. Can you advise what might cause this?

Many thanks

over 1 year ago

0 Youhao Xi over 1 year ago

TI__Guru* 78210 points

Hi,

Thank you for reaching out. The expert of this device is currently out of office. Please wait until early next week to get his reply.

Meanwhile, could you share your schematic and maybe some scope pictures of the SW, VIN and Vout signals?

Best Regards,

Youhao

0 Pjs over 1 year ago

Intellectual 890 points

Thanks Youhao.

I can not share the schematic publicly but am happy to send something through on a private channel.

Many thanks

0 Youhao Xi over 1 year ago in reply to Pjs

TI__Guru* 78210 points

Understood. I just sent you a private message through PMS.

Thanks,

Youhao

0 Richard Fu22 over 1 year ago

TI__Mastermind 31105 points

Hi,

Can you send over your schematic and scope picture of the SW, VIN, and VOUT via PM?

Thanks,

Richard

0 Pjs over 1 year ago in reply to Richard Fu22

Intellectual 890 points

Hi,

This issue has been resolved and was due to a measurement issue. Many thanks for the support.

Best regards