hcpl-7840 isolation amplifier problem

[466576266]

hello, anyone. i meet with a problem recently. as u can see from the picture.

let meassume that: the current through the shunt resistor is 20ARMS 50hz sinusoidal waveform, and the resistance of the shunt resistor is 5mohm. and now my question is:

1:what is the output of the pin7 of the hcpl-7840? how about the pin6? is it sinusoidal waveform?

2:what is the output of the mc34082a which is the pin7?

3:what is the function of the 150pF capacitor and 10kohm resistor connected to the pin5 of the mc34082a? and how to calculate the value?

thank u in advance.

 

[mister_rf]

1:what is the output of the pin7 of the hcpl-7840? how about the pin6? is it sinusoidal waveform?

Yes, if apply some sinusoidal waveform on the shunt resistor.
The HCPL-7840 consists of a sigma-delta analog-to-digital converter optically coupled to a digital-to-analog converter.

2:what is the output of the mc34082a which is the pin7?

A sinusoidal waveform, the output voltage has 5x the amplitude compared with voltage measured across shunt resistor.


3:what is the function of the 150pF capacitor and 10kohm resistor connected to the pin5 of the mc34082a? and how to calculate the value?


Details from the datasheet:

The post-amplifier circuit includes a pair of capacitors (C5 and C6) that form a single-pole low-pass filter. These capacitors allow the bandwidth of the pos-tamp to be adjusted independently of the gain and are useful for reducing the output noise from the isolation amplifier (doubling the capacitor values halves the circuit bandwidth). The component
values form a differential amplifier with a gain of 5 and a cutoff frequency of approximately 100 kHz and were chosen as a compromise between low noise and fast response times. The overall recommended application circuit has a bandwidth of 66 kHz, a rise time of 5.2 ms and delay to 90% of 8.5 ms.

http://www.datasheetcatalog.org/datasheet/hp/HCPL-7840.pdf

single-pole low-pass filter design:

Low-pass filter - Wikipedia, the free encyclopedia

 

[466576266]

thanks for ur reply.
assume that the waveform of the shunt resistor is sinusoidal which is centraled at zero. in this condition, how about the pin7 output? i know the waveform is sinusoidal now, but which is the center line of the waveform? and how about the output of the mc34082a? which is the center line? is it zero or some other value?
thank u.