AMC1300EVM: About noise on VDD1.

Kengo.Y

Guru 10385 points

Part Number: AMC1300EVM
Other Parts Discussed in Thread: AMC1300

Hi team.

I'd like to know about noise on VDD1.

I can see the noise at VDD1 that compared to not moving AMC1300.

Do you have any ideas to reduce this noise?

As shown in the data sheet, the VDD1 has 0.1uF and 2.2uF.

Sincerely.

Kengo.

over 4 years ago

0 Alexander Smith over 4 years ago

TI__Mastermind 47595 points

Hi Kengo,

This noise is most likely coming from whatever source is powering the AMC1300. I would recommend adding an LDO or a regulator to clean up the signal.

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Kengo,

I would try a pi-filter containing a ferrite bead.

Can you show a schematic?

Kai

0 Kengo.Y over 4 years ago in reply to kai klaas69

Guru 10385 points

Hi Alex, kai.

Thank you for your reply.

This waveform is with AMC1300 and without AMC1300.

So I think this noise is causing AMC1300.

Could you tell me what the behavior of AMC1300 causes this noise?

Sincerely.

Kengo.

0 kai klaas69 over 4 years ago in reply to Kengo.Y

Guru 140200 points

Hi Kengo,

I'm not clear what you want to say.

Can this noise be seen with the recommended decoupling caps mounted?

Kai

0 Kengo.Y over 4 years ago in reply to kai klaas69

Guru 10385 points

Hi Kai.

Yes.

We already had capacitors(0.1uF & 2.2uF) close to the VDD1.

Does AMC1300 produce noise at VDD1 ?

Sincerely.

Kengo.

0 Alexander Smith over 4 years ago in reply to Kengo.Y

TI__Mastermind 47595 points

Hi Kengo,

Can you share a picture of your schematic and layout?

0 Kengo.Y over 4 years ago in reply to Alexander Smith

Guru 10385 points

Hi Alex.

Could you check my customer's schematic and layout?

Sincerely.

Kengo.

0 kai klaas69 over 4 years ago in reply to Kengo.Y

Guru 140200 points

Hi Kengo,

the LT1761 has a poor ripple rejection at high frequencies. So, what you see at the AMC1300 could be the output ripple of ADUM5028 which punches through the LT1761.

What is the scope showing directly at the input and output of LT1761 and directly at the output of ADUM5028?

By the way, what is the purpose of TH1?

Kai

0 KAFEI GE over 4 years ago in reply to kai klaas69

Prodigy 10 points

I have similar question and let's see what he will reply.

0 Alexander Smith over 4 years ago in reply to Kengo.Y

TI__Mastermind 47595 points

Hi Kengo,

Unfortunately I am not an expert on power supplies, but I second Kai's concerns here. You could consult the appropriate forum for additional feedback as well.

Additionally, I think there is a slight error with your input capacitors. I imagine it was intended that 4700pf be the differential cap while 470pf's would be the common-mode caps.

I am also curious about the purpose of TH1 and R24.

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AMC1300EVM: About noise on VDD1.