INA828: Input bias current return path

user6371062

Part Number: INA828

Hi,

I have a question regarding the Input Bias Current Return path section (8.2) of the INA828 datasheet. I'm using this instrumentation amplifier to amplify signal from a wheatstone bridge. The Supply is +- 5V and ref is 2.5V. I do not think that I need to add this resistor to my design since the differential input source impedance is low. Adding resistor will increase noise in my system and also change the balance of the bridge. Please confirm.

over 5 years ago

0 Gerhard Kreuzer over 5 years ago

Expert 2600 points

.. correct, as long as there is a low impedance path between the inputs of the INA and ground.

With best regards

Gerhard

0 Raymond Zhang1 over 5 years ago

TI__Guru* 77521 points

Hi user6371062,

Thanks Gerhard for answering the question.

I'm using this instrumentation amplifier to amplify signal from a wheatstone bridge.

Your wheatstone bridge's ground is the input common-mode current return path for INA828's inputs. As Gerhard pointed out, you do not need to add extra resistors as shown in Figure 64 of the datasheet.

Best,

Raymond

0 user6371062 over 5 years ago in reply to Gerhard Kreuzer

Prodigy 70 points

Thanks for the Info.

Best Regards

0 kai klaas69 over 5 years ago

Guru 140200 points

No, you don't need this resistor. But if you would use it, you would take two identical resistors. Then they will not change the balance of bridge:

But that adding resistor(s) will increase the noise is wrong:

ina828.TSC

Kai

0 Raymond Zhang1 over 5 years ago in reply to kai klaas69

TI__Guru* 77521 points

Hi Kai,

Thanks for the circuit demonstration.

Best,

Raymond

0 user6371062 over 5 years ago in reply to kai klaas69

Prodigy 70 points

Yeah. I've made mistake. The input bias resistor is in parallel with bridge resistor and total noise will be even smaller than the smaller one of that 2 resistor.

0 kai klaas69 over 5 years ago in reply to user6371062

Guru 140200 points

Exactly :-)

Kai

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INA828: Input bias current return path