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Original question:

AMC1300B-Q1: SPWM Measurement using AMC1300B

THS4131: THS4131 as output as fully differential output

Rajasekaran
Intellectual 945 points
Part Number: AMC1300B-Q1
Other Parts Discussed in Thread: THS4131, AMC1300

Dear sir,

We are using AMC1300 for isolated voltage measurement and its output is connected to THS4131 amplifier. 

THS4131 having +/-12V power supply. 

+12V : Vcc+ of THS4131

0V : Vocm of THS4131

-12V : Vcc- of THS4131.

The THS4131 amplifier output is given to NI 9220 analog input module. When we connect the THS4131 output to NI 9220 analog input module, the measurement are floating.

We need to connect the 1MOhm resistor between analog input negative terminal and common terminal. 

When we connect the 1MOhm resistor, we can able to measure it normally. 

Cloud you please suggest the procedure to get the fully differential output from THS4131 amplifier. 

Thanking you.

Thanks & Regards,

Rajasekaran.

  • 0
    TI__Genius 15555 points

    Hello Rajasekaran,

    The output of the THS4131 shouldn't be floating as the Vocm pin of the device determines the output common-mode. There shouldn't be a need to add an additional 1M-ohm resistor, and in fact this will just cause an imbalance due to differing loads on the FDA outputs. Can you measure the inputs and outputs of the THS4131 using a scope?  

    Best,

    Hasan Babiker