AMC3330EVM: about 4.1 Analog Inputs: J2

R.Fukunaga

Part Number: AMC3330EVM
Other Parts Discussed in Thread: AMC3330

Tool/software:

Hi all,

2 and 3 of J2 of AMC3330 were shorted and tested referring to the following data sheet.

"7.3 Best Design Practices
Connect the high-side ground (HGND) to INN, either directly or through a resistive path. A DC current path
between INN and HGND is required to define the input common-mode voltage. Take care not to exceed the input common-mode range as specified in the Recommended Operating Conditions table."

1Vp-0 waveform was designed between INP and INN as an input signal, and Pins 1 and 2 were measured with a differential probe.

However, only 60mVp-0 was actually observed.

What measures and settings are necessary to correctly measure the waveform of 1 Vp-0?

Do you know the cause?

In addition, when pins 1 and 2 of J3 were measured with a differential probe, the output waveform was 2Vp-0, which was as designed.

The circuit diagram, conditions, and waveform are shown below.
Input voltage: AC5Vp-0
Pins 1 and 2 were measured with a differential probe.

Best Regards,

Ryusuke

1 month ago

0 Tom Hendrick 1 month ago

TI__Guru**** 181441 points

Hi Fukunaga-san,

I'm not aware of anything that would cause so much attenuation of the input signal, and 60mV pk on the analog input should not get you 2V pk on the outputs. Can you provide a screen shot of the output voltage compared to the input?

0 R.Fukunaga 1 month ago in reply to Tom Hendrick

Expert 2595 points

Hi Tom,

I'm sorry. This is the waveform of the output side.

Best Regards,

Ryusuke

0 Tom Hendrick 1 month ago in reply to R.Fukunaga

TI__Guru**** 181441 points

Can you take a picture of the EVM and get the top side marking of the chip please?

0 R.Fukunaga 1 month ago in reply to Tom Hendrick

Expert 2595 points

Hi Tom,

1) IC

2) Board front

3) Board back

Best Regards,

Ryusuke

0 Tom Hendrick 1 month ago in reply to R.Fukunaga

TI__Guru**** 181441 points

Thank you! I don't see anything that looks out of the ordinary. What signal source are you using?

0 R.Fukunaga 1 month ago in reply to Tom Hendrick

Expert 2595 points

Hi Tom,

My customer uses Function Generator below.

33120A 15MHz ファンクション/任意波形発生器 [販売・サポート終了製品] - キーサイトFunction Generator / Waveform Generator

Best Regards,

Ryusuke

0 Tom Hendrick 1 month ago in reply to R.Fukunaga

TI__Guru**** 181441 points

OK - lets try this - can you look at INP and INN relative to HGND? Can you also verify that the 10nF cap on the EVM was removed?

0 R.Fukunaga 1 month ago in reply to Tom Hendrick

Expert 2595 points

Hi Tom,

Thank you for your advice.

''Can you also verify that the 10nF cap on the EVM was removed?''

→I understand that the 10nF cap is C12 and has been removed from the picture above.

Do I need to make any changes?

Best Regards,

Ryusuke

0 Tom Hendrick 1 month ago in reply to R.Fukunaga

TI__Guru**** 181441 points

C12 is correct, and I do see it is not there. To make this a little easier on you, instead of the two 5M resistors in parallel (2.5M effective) can you split that connection into two 1.25M resistors? Tie one end of each 1.25M to HGND, remove the short between pins 2-3 on J2 and use the 5M in series to pin 1 and pin 2 with the 1.25M to HGND like this:

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AMC3330EVM: about 4.1 Analog Inputs: J2