ISO224: About ISO224 output noise peak

Yanni Li

Intellectual 1960 points

Part Number: ISO224

HI team,

My customer has problems in circuit design.

When he use iso224, Its output has some short-circuit noise peak, the highest one is -87db. In particular, when he change another Iso224b,the noise peak will appear at different frequencies. For example, the noise peak of this chip at 430hz, and the noise peak of another chip at 1kHz.

His circuit is as follows，Thank you.

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi Yanni,

I would remove L2 for a test.

Also, are the supply voltages well regulated and noisefree?

Kai

0 Alexander Smith over 3 years ago in reply to kai klaas69

TI__Mastermind 47595 points

Hi Yanni,

Let me send a note to the team to see if they have any thoughts.

0 user6329816 over 3 years ago in reply to kai klaas69

Prodigy 55 points

I remove L2 ,but Noise is constant,and supply voltages well regulated and noisefree,

When I input the signal, the noise is still there

0 kai klaas69 over 3 years ago in reply to user6329816

Guru 140200 points

Hi Yanni, hi User,

what do you mean by "short-circuit noise"?

Does the noise change, if you take another OPAmp at the output of ISO224?

Kai

0 user6329816 over 3 years ago in reply to kai klaas69

Prodigy 55 points

HI KAI

I have tried, but the noise has not changed, I think the noise is independent of the output, because I detected the noise in Vp and Vn. And this noise is not only short-circuiting noise, it's always present when the signal is input.

During the test, I found that when I changed the input impedance, the noise point changed, and I found that when I removed the capacitance of the VCAP pin, the noise of some chips disappeared, but some chips had no effect

0 kai klaas69 over 3 years ago in reply to user6329816

Guru 140200 points

Hi User,

what happens, if you directly connect pin 2 of ISO224 to pin 4 of ISO224?

Kai

0 user6329816 over 3 years ago in reply to kai klaas69

Prodigy 55 points

hi kai

The noise is always there, and the noise point does not change

0 kai klaas69 over 3 years ago in reply to user6329816

Guru 140200 points

Hi User,

strange... Let's see what the TI's experts say about this.

Kai

0 Alexander Smith over 3 years ago in reply to kai klaas69

TI__Mastermind 47595 points

Hi,

The idle tone frequency will vary from device to device and will be a function of DC level at the output.There are usually no significant tones in the kHz range

The tones can be caused by switching noise coupling to reference. Since the reference doesn’t come out on chip in this part it must be through supply/ground path.

Can you provide a capture of the layout so we can try to identify the source of the noise?

I see that the viewing window of the spectrum analyzer is set to only 20kHz, if this is increased to 1MHz, are you able to see more significant tones at higher frequencies?

0 user6329816 over 3 years ago in reply to Alexander Smith

Prodigy 55 points

Do you need A PCB image or a design file?

How should I send this document to you?
Is it to your email address？

0 Alexander Smith over 3 years ago in reply to user6329816

TI__Mastermind 47595 points

Hi,

PCB image posted here on the forum is fine. If you would not like to post this PCB image, let me know and I will contact you offline.

0 Alexander Smith over 3 years ago in reply to Alexander Smith

TI__Mastermind 47595 points

Hi,

Thank you for providing the schematic and layout. As I asked before, I see that the viewing window of the spectrum analyzer is set to only 20kHz, if this is increased to 1MHz, are you able to see more significant tones at higher frequencies?

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ISO224: About ISO224 output noise peak