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Original question:

AMC3330-Q1: AMC3330 input signal layout suggestion

AMC3330-Q1: Schematic review for AMC3330

Zoe Yang
Intellectual 1830 points
Part Number: AMC3330-Q1
Other Parts Discussed in Thread: AMC3330

Dear team,

My customer is using AMC3330 in HVbus voltage sampling, the input signal configuration is shown in below figure. Would you please help comment if input RC component value is correct? 

HVbus norminal=400V.

  • 0
    TI__Intellectual 1830 points

    And would you please help comment on how to protect on the INP and INN? Is TVS needed to prevent if input breakdown？

  • 0 in reply to Zoe Yang
    TI__Mastermind 47625 points

    Hi Zoe,

    Does the customer want to measure a maximum voltage beyond the nominal? 

    In their current system I calculate an input voltage of 330mV when 400V is applied, which does not use the full 1V input range of the AMC3330. 

    400*3.3k/(4M+3.3k+200) = 329.7mV. 

    I also see the sense resistor as 3.3kohm, not 3kohm and do not understand why an additional 200ohm resistor is placed between the sense resistor and AGND. 

    Can you please ask the customer if this is their intended design? 

  • 0 in reply to Alexander Smith
    TI__Intellectual 1830 points

    Adding additional 200ohom resistor is referring to our reference layout showed on our datasheet. The input filter not only suppresses EMI and noise entering the ciruit from the left but also suppresses the chopping noise leaving the input pins of AMC3330. And would you please help comment on how to protect on the INP and INN? Is TVS needed to prevent if input breakdown？

  • 0 in reply to Alexander Smith
    TI__Intellectual 1830 points

    Vin=200V~1000V normal=400V, that's why they consider 330mV input signal. Is that OK?

  • 0 in reply to Zoe Yang
    TI__Mastermind 47625 points

    Hi Zoe,

    It is fine, they could increase the size of the sense resistor to match the input voltage range if they desire. As Tom mentioned in the other thread, RL12 is not necessary, it is there to show what kind of application the device enables, such as a line-line measurement. 

    TVS should not be needed on the inputs. If you refer to the absolute maximum ratings in the datasheet you will see that the input voltage can go beyond the high side supply and well below ground. If there is worry from the customer, I recommend limiting the amount of current that may through the inputs.