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THS4151: Filter component selection guidance

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Replies: 16

Views: 251

Part Number: THS4151

hi,

we are designing the amplier for the voltage measurement circuit. AMC1300 is used as isolation amplifier for voltage measurement. Its output is given to THS4131.

we are facing noise in the amplifier output and the noise signals are in the range of +/-12V. we are guessing that these noise are added into the circuit due to THS4131. 

we are trying to add the low pass butterworth filter at the amplifier output as shown in the circtuit below. 

Input voltage to AMC1300 : 75mV

Output voltage from AMC1300 : 615mV

R1 : 402 Ohm

R2 : 4020 Ohm

gain : 10

signal frequency : 15kHz

we ignored the filter components R3, C1,C2, R4 and C3.  we are facing +/-10V noise signal in our output. 

Please guide us to select the values for R3, C1, C2, R4 and C3. 

Thanking you.

Thanks & regards,

Rajasekaran.

  • Hello Rajasekaran,

          R4 and C3 are not part of the filter components which is referenced in the provided Figure 35; instead, they are part of Figure 34 explaining the affects of driving a capacitive load. A isolation resistor, R4, and an active anti-aliasing low-pass filter are important in eliminating the high frequency noise and oscillation that comes with capacitive loading which is commonly seen when interfacing with ADCs. From the provided schematic of your application, there does not appear to an external capacitive load. Would you be able to share scope shots at the output of the isolation amplifier? 

    Thank you,

    Sima

  • In reply to SimaJalaleddine:


    hi,

    Now we removed the amplifier THS4131. and AMC1300 isolation amplifier only connected to the circuit.


    In the output of AMC1300, R90 and R92 24 Ohm resistance is connected as load. Please find the attached below waveform & FFT for the inverter output voltage measurement.

    Inverter carrier frequency : 5kHz

    Load : Resistive load

    DC bus voltage : 65V

    Expected voltage accross R91 : 8mV and AMC1300 output is : 65.6mV.

    Kindly guide us to remove the noise in the AMC1300 output.

    Thanking you.

    Thanks & regards,

    Rajasekaran

  • In reply to Rajasekaran:

  • In reply to Rajasekaran:

    Hello,

    AMC1300 is not the best choice for voltage sensing measurements as the low-input impedance and higher input bias currents will negatively interact with the voltage divider on the input causing large offset and gain errors.

    AMC1311 is optimized for voltage sensing, has high >1GOhm input impedance and is in the same package as the AMC1300.  Can you try the AMC1311?

    That aside, if you'd like us to help debug the current situation more effectively please take differential scope measurements (not digitized labview results) directly at the inputs and outputs of the AMC1300.

    Regards,
    Collin Wells
    Precision ADC Applications

  • In reply to Collin Wells:

    In addition to Collin's comments, is GND1 (MHV3-) referenced to the input nets VM_B and VDC_0V?

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources: BIO-FAQ: Common Questions for TI's ADS129x Family of Bio-Potential ADCs

    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

  • In reply to Alexander Smith:

    hi,

    Today we removed the circuit from high voltage. 

    we applied 4mV at 20kHz sine waveform between VIN_P and VIN_N of AMC1300. we can able to measure the 314mV across OUTH and OUTL of AMC1300.

    Also we can able to measure 3.24V across VOUT+ and VOUT- of THS3141. 

    We can able to observe  the correct functioning of AMC1300 and THS3141 in the circuit. 

    When we applied 24V across DC bus, we can able to get SPWM pulses across  VM_B and VDC_0V. But we test it across R87, R88, R91, R94, R96 we are unable to measure the SPWM pulses. we will verify the same and upate you again. 

    Thanks for your kind support. 

    Thanks & regards,

    Rajasekaran

  • In reply to Rajasekaran:

    hi, 

    the circuit is, 

    Please find the attached waveform for the AMC1300 output. 

    Click here to play this video

    Please find the THS4131 output waveform.

    We are applying SPWM to the single phase inverter. 

    VM_B and VDC_0V is voltage accross the switch. 

    MHV3- and MHV3+ is separate isolated DC-DC source 

    M5V- and M5V+ is separate isolated DC-DC source

    PS12V- and PS12V+ is separate isolated DC-DC Source. 

    The final output of THS4131, we are getting the noise in the same level of Power supply voltage. Kindly let us know the procedure to eliminate the noise. 

    Thanking you. 

    Thanks & regards,

    Rajasekaran

  • In reply to Rajasekaran:

    Hi Rajasekaran,

    I'm not able to view the first video, but I can see the second. Can you repost the AMC1300 output video in the same format as the THS output video? 

    MHV3- and MHV3+ must be referred in some way to VM_B and VDC_0V which I do not see on the schematic. This connection marked in red can be made either at the input of the AMC1300B device, or where the isolated power supply is being derived. 

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources: BIO-FAQ: Common Questions for TI's ADS129x Family of Bio-Potential ADCs

    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

  • In reply to Alexander Smith:

    hi,

    please find the below waveform for the AMC1300 output.

    Also please find the below attached complete schematic for the inverter voltage and current measurement. 

    converter_v1_0.pdf

    Queries : 

    1) We are using 6 AMC1300B in our project and we are using six isolated power supply for the same. Do we need to connect the VIN and GND1 of each AMC1300B? kindly confirm. 

    2) Shall we connect the GND1 and VIN of AMC1300 in IC Pins directly or do we need to connect before the RC Filter? Kindly confirm. 


    Thanks & regards,

    Rajasekaran. 

  • In reply to Rajasekaran:

    Hi Rajasekaran,

    Thank you for providing the video. 

    Yes, VINN and GND1 of each AMC1300B should be connected. 

    They should be connected before the RC filter. 

    Please give this a try and let me know the results.

    Best regards,

    Alex Smith
    Applications Engineer | Precision Delta-Sigma Converters

    Check out our helpful resources: BIO-FAQ: Common Questions for TI's ADS129x Family of Bio-Potential ADCs

    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator Data Converters Learning Center | Selection Guide

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