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AMC1035-Q1: Increased input bias current of AMC1035-Q1, if no clock signal is provided.

Andreas Hofschweiger
Prodigy 35 points
Part Number: AMC1035-Q1
Other Parts Discussed in Thread: AMC1035

Tool/software:

Hello TI-support team,

I have a question regarding the delta-sigma modulator AMC1035-Q1. In the datasheet, section "7.3.4 Clock Input", it is described that the component experiences an increase of input bias current beyond the specified range, when no clock is provided in the specified frequency range.

I have a use/fault case in my application, whereby the clock signal will not be provided under some special circumstances and therefore a higher current will be given in the measurement path through this behavior. Since there is some additional functionality provided via the voltage divider measurement path, this behaviour influences my circuit. 

Therefore, my question regarding the increase of the input bias current. Is it possible to specify the input bias current (max), when there is no clock signal given (or the minimum input impedance of the circuit during this fault scenario)?

BR

Andreas

  • 0
    TI__Guru**** 181641 points

    Hi Andreas,

    Sorry for the delay in getting to your post!  Without the clock running the internal charge pump is not functional.  Negative voltage on the inputs will see a diode and resistor (~10k) to ground.  Positive input voltages should still see a high impedance.  I don't have an absolute number for you as it is very non-linear and will depend on the impedance of your driver/signal chain connected to the inputs of AMC1035.

  • 0 in reply to Tom Hendrick
    Prodigy 35 points

    Seems somehow strange, since I experience some other behaviour. I still have a positive input voltage over the differential inputs of the AMC1035 (ANIP, AINN) and the circuit behaviour changes, so there might also be some other circuit characteristics for a positive voltage.. Is that really correct, that with positive input voltages there is not change in input circuit impedance?

  • +1 in reply to Andreas Hofschweiger
    TI__Guru**** 181641 points

    Hi Andreas,

    I heard back again today from another person who is more familiar with the internal design.  He says that both inputs are seeing a diode and closer to 4K (not 10k).  Still non-linear and dependent on your input signal chain.