Understanding of Hardware Circuit

[electronicsman]

I am trying to understand the following hardware circuit mainly for current sensing portion.
https://obrazki.elektroda.pl/1033430900_1504148974.png
https://obrazki.elektroda.pl/5114444000_1504149148.png

For one he is using VREF and the other Gnd. Why it has to be used like that? I do not how the op amp in this configuration works?

https://obrazki.elektroda.pl/6809253100_1504149312.png. Why he should use 0 ohm resistor?

 

[barry]

Without seeing the rest of the circuit, it's hard to answer your question. But the circuit is a basic difference amplifier.

 

[FvM]

The circuit is a basic single OP differential amplifier. Vref respectively GND are different output references, chosen according to the intended usage.

Vref is for bipolar input current/voltage range with an unipolar ADC (e.g. 0 to 3.3 V ADC range, output = 1.65 V with input zero). GND is for unipolar input range.

The 0-ohm resistor is used as "net connector". SHUNT_LOW_SUM is connected to DC- net, but should be wired separately between shunt and amplifier input to achieve a 4-wire (kelvin sense) connection, avoiding errors due to DC- net voltage drops. The 0-ohm resistor is a trick used with simple PCB layout systems that don't support star points or net connectors.

 

[electronicsman]

Without seeing the rest of the circuit, it's hard to answer your question. But the circuit is a basic difference amplifier.

I am sorry i did not mention but the schematic is in the last pages of the attached pdf document.
Ok i will just study about difference amplifier.

 

[FvM]

Amplifier output voltage is Vshunt * 150k/2k + Vref.

Using split input resistors and a capacitor introduces a low-pass filter. The about 3 MHz cut off frequency is however far beyond 135 kHz amplifier bandwidth and thus effectively useless.