LM2672 Connecting SYNC pin to GND

masahiko shimizu

Guru 11235 points

Other Parts Discussed in Thread: LM2672

My customer uses LM2672 at SYNC pin open. They is making their muss product now.

They have a issue that output voltage has spurious around 10Mhz. (Output voltage has noise)

They connected SYNC pin to GND through 1k-ohm.

Then, this issue is solved at their most product. But they have this issue at some product.

Q1: Can SYNC pin connect to GND directly? *They use internal oscillator.

Q2:　How small resistance is allowed for pulldown of SYNC pin?

Best regards

Shimizu

over 10 years ago

0 Anston Lobo over 10 years ago

TI__Genius 16025 points

Hi Masahiko,

We are looking into your request right now and will get back to you shortly.

Thanks,

Anston

0 Akshay Mehta over 10 years ago

TI__Genius 15810 points

Hello,

The datasheet doesn't talk about grounding the SYNC pin when the internal oscillator is used but in fact leaving it open. There is a 50k resistor internal to the pin going to ground and we haven't spec'ed an external pull down resistance. Have you tried using small value ceramic capacitors on the output to get rid of the noise? One method is to use ceramic caps whose SRF is the same as the frequency of ringing on the output. This should help.

Regards,
Akshay

0 masahiko shimizu over 10 years ago in reply to Akshay Mehta

Guru 11235 points

Hi Akshay

Thank you for your support.

I will try your advice method.

Best regards,

Shimizu

Power management

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LM2672 Connecting SYNC pin to GND