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AMC0311R-Q1: Max Analog input limit

ABKD
Intellectual 610 points

Part Number: AMC0311R-Q1
Other Parts Discussed in Thread: AMC0311R

Hello,

For AMC0311R-Q1 the recommeded conditions are given as -

image.png

But the absolute max ratings are as below -

image.png

So as per above absolute limit of upto 7V, can I apply 4.81V to the input for below application -

image.png 

Here, Vin = 5V; the NTC max voltage goes to 4.81V and R1 = 68 kohm and min. 170mV

Can I directly inteface AMC0311R-Q1 to above circuit ?

  • 0
    TI__Prodigy 170 points

    Hello ABKD,

    as the datasheet explains under the table 6.1, the maximum ratings specifies the operating conditions under which the device won't be damaged permanently. The maximum ratings do not ensure proper device functionality. Only when you stay within the recommended operating conditions specified under 6.3 the device will function properly. As a result your input voltage is limited from 0.077V to 2.25V. Going beyond this range your signal will start to clip once it reaches 0V or 2.56V.

    For your application you need to first scale your signal to the 0.077V to 2.25V input range of the AMC0311R. Directly applying your signal to the AMC0311R will not work since the device can't measure voltages up to 4.81V.

    Best regards,

    Simon

  • 0 in reply to Simon Nielebock
    Intellectual 610 points

    Hello Simon,

    I agree with you, the signal beyond 2.25V at input won't be measured by opamp.

    But can this opamp input sustain this much voltage 4.81V ?

    In addition to this the R1 = 68 kohm for limiting the current to opamp and NTC.

    Please let me know.

  • 0 in reply to ABKD
    TI__Expert 7560 points

    Hi ABKD,

    The opamp will be fine with the input voltage at 4.81V if the VDD>4.5V, but as Simon mentioned your measurement will be clipped.

    Also, keep in mind the internal impedance of the device relative to the NTC impedance as it may affect your measurement since they would be in parallel. 

    Thanks..

  • 0 in reply to Saleh Ahmad
    Intellectual 610 points

    Hello Saleh,

    Thanks for your response.

    As per datasheet the input impedance is 2.4 Gohm.

    This is quite high.