THS4151: Filter component selection guidance

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

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

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.

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

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

hi, 

the circuit is, 

Please find the attached waveform for the AMC1300 output. 

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

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. 

hi,

Thanks for your continuous and kind support to solve our issue. 

Now we can able to measure the voltage and current without noise issue. 

Voltage measurement. 

Current waveform

Once again thanks for your support 

Thanks & regards,

Rajasekaran.

Great news Rajasekaran, thank you for letting us know! 

Please feel free to start a new thread if you have additional questions or concerns. 

Dear sir,

Thanks for your guidance to eleminate the noise in the AMC1300 measurements. 

When we measure the current signal it works good. 

When we try to measure the voltage signal, we are getting the constant DC offset. 

Voltage and current signal measurements when there is no load voltage / current is applied. 

Yellow - Voltage measurement output. 

Blue - Current measurement output. 

we need to measure both AC and DC Voltages. 

How to remove the DC offset in the voltage measurement circuit of AMC1300. 

Thanking you. 

Thanks & regards,

Rajasekaran

Dear sir,

Kindly provide the following details to use the gain and offset error excel calculator.

1. INL value for AMC1300B.

2. INL Drift value for the AMC1300B

3. Rdivider impednace ( Equivalent impedance (Ω) of the resistor divider) : Is it equivalent resistance of Rsense and RIN of AMC1300B ( our Rsense is 1kOhm and RIN for AMC1300B is 19kOhm) The equivalent resistance is : 950 Ohm.

4. GE Rdivider Drift is calculated as (for 50ppm)  : (100)*50*10^-6 (ppm) * 0.25 * 10^3 (full scale input voltage in mV). what is meaning of 100 in this equation.

5. Offset error Rdivider (Offset from bias current and divider resistance (Rdivider * Ibias))

is calculated as "Rdivider impedance x 0.000032 / full scale voltage). what is the meaning of 0.000032 in this equation ?

6.Offset Rdivider Drift of AMC1300B. 

Thanks.

Thanks & regards,

Rajasekaran