INA202: INA202

CLAVERIE Alain

Intellectual 410 points

Part Number: INA202
Other Parts Discussed in Thread: INA190, INA114, LMC6062

I re-open this subject

The generator now delivers stable 29.56 ua

but il need to add a current monitor which will control max current about 1MA in case of problem with tue generator

I've chosen an TI INA202

I insert a shunt of 10 ohms between generator and load which car vary between 100k and 350 k as already explained before

I get the following problem

load under 200 k .. the current generator pass from 29.56 to 30.5 uA ?????

not a big problem but

when I put a

300 k load .. current fall to 25 uA !!!

I don't understand why ? I've checked that 2.5 V is always on resistor 91k of the generator..

I know that a part of current is to the inputs of the INA 202 but?

Could you help ?

if necessary I will post a new subject..

Thanks

over 6 years ago

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Claverie,

datasheet of INA202 mentions that the input bias current of INA202 is up to +/-16µA, which is in the same order of magnitude as your signal current. So, this circuit will not work properly.

Kai

0 Javier Contreras4 over 6 years ago

TI__Mastermind 29630 points

Hello Clavarie,

Thank you for using the forum to get you questions answered. Along with your input bias current being in the same level as your measurement you will have two other issues. As your Vsense changes your input bias currents will also change. The larger issue I beleive is that you are not using the INA202 in the optimal region. 7.4.2 in the datasheet. You will see that you are operating in the Low Vsense Case 2 Condition and the INA202 is not optimal when Vsense is below 20mV. There is futher detail for that case in section 7.4.2.4

0 CLAVERIE Alain over 6 years ago in reply to Javier Contreras4

Intellectual 410 points

Hi everybody
First thank you for you quick answers
Do you have an idea of with TI module I can use for my application ?
Regards

0 Javier Contreras4 over 6 years ago in reply to CLAVERIE Alain

TI__Mastermind 29630 points

Hello Claverie,

The INA190 has low input bias current but the supply voltage and output voltage is limited to 5.5V. Another few difference from the INA202 are the INA190 has lower bandwidth, different gain options, and there is no integrated comparator. Our integrated comparator parts have larger IB than the INA202 so with that regard that may not be optimal.

Our instrumentation amplifiers could also be an option. I saw you post something with the INA114 for the same question.

0 CLAVERIE Alain over 6 years ago in reply to Javier Contreras4

Intellectual 410 points

hi again
In fact I've posted for the INA114 but It was for the design of the current generator
I never succeed to have a enough good stability of the 30 UA current source depending of the load
SO TI propose me the cicruit with the LMC6062 above and it works
But I need to add a security on the possible current and I llok for the right solution
Till now all circuit I have tested cause modification of the current fot high value of load (300K)
tomorrow(in France..) I ll test an INA114 beacause bias current seems low
regards

0 kai klaas69 over 6 years ago in reply to CLAVERIE Alain

Guru 140200 points

Hi Claverie,

to be able to make the INA114 properly work you should download the "Vcm vs Vout Calculator for Instrumentation Amplifiers (Rev. I)" from this link:

www.ti.com/.../toolssoftware

Kai

0 Javier Contreras4 over 6 years ago in reply to kai klaas69

TI__Mastermind 29630 points

Hi Claverie,

I believe the solution could be the INA190 or the INA114. Please let me know if you would need further help on this.

0 CLAVERIE Alain over 6 years ago in reply to Javier Contreras4

Intellectual 410 points

Hi
I've not yet recevived components . I'll keep you informed
INA190 is not possible for my application because of BGA packaging

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INA202: INA202