OPA2388: Instrumentation amplifier Schematic review

subash surendaran

Part Number: OPA2388
Other Parts Discussed in Thread: INA317, , INA188, INA333, INA826S, INA826

Hi,

We are developing a infusion pump, and it has a occlusion sensor section and we are using a Wheatstone bridge in the circuit to detect the occlusion(load).

The sensor we are using is beam sensor from Forsentek (FMZK-10kg) with the spec below.

Rated Output       1.0±0.1mV/V

Excitation      3~10 V

Zero Balance      ±0.1mV/V

As we are supplying 10V to the loadcell , it will be 9mV to 11mV differential output from the load cell.

Zero balance will be ±1mV, which means the minimum output will be -1mV (no load) and max output will be 11mV (full load)

We are using OPA2388IDR 2 circuit opamp to build a instrumention amplifier (Buffer/amplifier section only ,No differential amplifier) to amplify the load cell output and to produce a differential output.

The gain set is 285 (R =200000Ω,Rg=1400Ω). So that the output will be -286mV to 3146mV.

Will this circuit connection and supply voltage correct to handle negative input voltage?

Being single supply design, will the output be guaranteed for linear output?

over 3 years ago

0 Raymond Zhang1 over 3 years ago

TI__Guru* 77501 points

Hi Subash,

subash surendaran said:
Being single supply design, will the output be guaranteed for linear output?

If the circuit is implemented in a single supply, you have to implement Vref voltage as shown in the simulation below. It is unable to output -0.286V to 3.146V from a single supply, unless dual supply rails are used. The simulated circuit below did not optimize your op output voltage range.

INA188 Single Vs 12122022.TSC

I do not recommend to build instrumentation amplifier (IA) with discrete OPA2388 op amp. Since OPA2388 is a zero drift op amp, I selected INA188 for the application. You may also use our low power INA333 or INA317 op amp for the application.

To build the IA in discrete components will increase your overall cost. The resistor matching is very critical to build high CMRR IA, and our IA's internal resistor matching is better than 0.01% or 100ppm range.

Enclosed is 2-op IA circuit application note. And I do not recommend to build a discrete IA.

https://www.ti.com/lit/an/sboa281/sboa281.pdf?ts=1670843742587

If you have further questions, please let us know.

Best,

Raymond

0 subash surendaran over 3 years ago in reply to Raymond Zhang1

Prodigy 10 points

Hi Raymond,

Thanks for your reply. I've seen the op amps you suggested they are Precision IA's but they are not easily available in bulk in market or from TI. Also previously we were using PGA281AIPWR which has a differential output but it went out of stock and has a long lead time that's why we were trying to replicate a differential output from the IA using Op amp. But now we are ready to go with single ended output and we decided to use INA826SIDRCR which is also a Precision IA also available in stock, do you think it's a good idea ,what is your suggestion?

Thanks and Regards,

Subash

0 Raymond Zhang1 over 3 years ago in reply to subash surendaran

TI__Guru* 77501 points

Hi Subash,

subash surendaran said:
do you think it's a good idea ,what is your suggestion?

INA826SIDRCR is a great IA for the strain gauge application. I recommended INA188 or similar because I thought you are looking for zero drift IA specifically (OPA2388 belongs to zero drift op amp series.).

The INA826SIDRCR stock status in TI e-store is shown below. INA826S and INA826 have the same design, except INA826S has shutdown pin feature that INA826 did not bring it out.

You may consider to plan and get certain hard find components while they are in stock. Sometimes, you may not be able to find these when you really need it in the current market conditions.