INA 210 Vref input resistance and gain control.

Nir Porat

Other Parts Discussed in Thread: INA210, OPA333, INA210-215EVM

Hello,

I have two questions :

1.What is the input resistance allowed on the Vref input of the INA 210 (could not find any inputs on the data sheet)?

2.Can i control the gain using Mohm resistors at the amplifier V+,V-?( I would like to achieve gain of 300 for instance )

over 9 years ago

0 Rabab Itarsiwala over 9 years ago

TI__Expert 4595 points

Hello,

Let me look into this and get back to you.

0 Rabab Itarsiwala over 9 years ago in reply to Rabab Itarsiwala

TI__Expert 4595 points

Hello,
1. Please refer to section 8.4.3 on the INA210 datasheet for REF input impedance effects.
2. Adding resistors in series with the inputs is not a good way to reduce gain. Since the absolute value of the internal resistors may vary 20% (only the ratios are matched to the given accuracy) this way of changing gain will introduce errors. You can reduce gain at the output by using a resistor divider if you don't need full output range.
If you can share some details of your application, we may be able to provide better suggestion (Supply voltage, Common mode voltage, differential volatage range ( or load/shunt current), Reference Voltage and desired output range).

0 Nir Porat over 9 years ago in reply to Rabab Itarsiwala

Intellectual 590 points

Thank you for your answer ,

however i understand that i must use an op amplifier,

"When using resistive dividers from the power supply or a reference voltage,
the REF pin should be buffered by an op amp "

Yet i have tried to use Vref with voltage divider and it seems to work fine, is there is particular reason why op amp is required?

0 Nir Porat over 9 years ago in reply to Nir Porat

Intellectual 590 points

I am using 3V voltage and, need vref of 1-1.5V, i would like to use voltage divider.
Is there any suggestion op amplifier?

0 Rabab Itarsiwala over 9 years ago in reply to Nir Porat

TI__Expert 4595 points

The reason is that any impedance on the Reference Pin would affect the Common-mode rejection Ratio. You may use something like a OPA333.

0 Nir Porat over 9 years ago in reply to Rabab Itarsiwala

Intellectual 590 points

Is there any graph which can demonstrate the CMRR versus the input resistance?

0 Rabab Itarsiwala over 9 years ago in reply to Nir Porat

TI__Expert 4595 points

Hi,We do not currently have a graph to demonstrate this characteristics.

0 Nir Porat over 9 years ago in reply to Rabab Itarsiwala

Intellectual 590 points

Is there any resistance that can be used without any issues?

0 Jason Bridgmon over 9 years ago in reply to Nir Porat

TI__Genius 14825 points

We don't really have a recommendation for this as it varies according to desired application parameters and allowable tolerances. Also, we cannot guarantee any application design support we offer to not have any issues.

We would like to help you, but perhaps you could tell us a bit more about your desired specs, end application, product, company, what you have looked into/debugged so far, and the expected volume of sale. There is an EVM (INA210-215EVM) available for the INA21x family of products. Have you tried one? This could help you measure some of what you are asking about and can help you make a more informed decision, far better than we can offer sight-unseen.

Please let us know how we can assist you further.

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INA 210 Vref input resistance and gain control.