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LMV358A: Opm generates output voltage even when no signal is input

vijay kumar
Prodigy 30 points

Part Number: LMV358A
Other Parts Discussed in Thread: TMS320F28069M

Tool/software:

Hi,

Our requirement is to digitize the analog signal to digital pulses. These analog signals source is voltage rise/fall in electrical wires.

  • Below is schematic snippet. The input analog  signal voltage is 1V, aplified votage is 2.5V and amplification operating voltage 5V.

This Opms set helps to amplify the input analog signal.

      

The second Opms set helps to digitize the the signal into pulses.

  • The correct output from second stage (D_OUT_MCU) when input analog signal is provided to first stage (Clam_Input_Current).

  • However, if there is no input to first stage, but still output at second stage is found, which is not needed and we are debugging. The D_OUT_MCU is connected to MCU pin configured for Compare&Capture(eCAP), MCU (TMS320F28069M). This behaviour is inconsistent, in some of the custom pcb boards, the noise signal is not present. 

Need help to find out the cause if the noise signal.

Thanks.