INA125 offset circuit

[strasni_betmen]

Hi all,

INA125 offset circuit from datasheet is in the attachement. I have some questions about it:
1. what do "100uA" and "1/2 REF200" markings mean?
2. can I use LM358 instead OPA237?
3. I built the circuit using LM358 with V+ = 10V, V-=-10V and those 100Ohm resistors got pretty hot, I don't think it's the way to go, why is that???
4. are 100Ohm resistors valid ones or do I need bigger resistors?

Kind regards

 

[keith1200rs]

1. look at the data sheet for the REF200 - it should then be clearer https://www.ti.com/lit/ds/symlink/ref200.pdf It is a dual precision 100uA current source.

2. the LM358 would have worse performance due to higher bias current, offset voltage and offset voltage drift

3. I guess you didn't include the REF200!

4. no, you need the REF200.

Keith

 

[strasni_betmen]

Thank you for clarification!

I just searched for REF200 on several of my local dealers pages and could't find one, how good is LM334 replacement?
Can somebody please suggest what other options do I have?

King regards

 

[keith1200rs]

It really depends on how much precision and stability you are looking for. A 50k resistor to a 5V supply will give you roughly 100uA but without the 0.5% precision of the REF200, depending on the accuracy of your 5V. The LM334 has a current proportional to absolute temperature so isn't a great replacement.

If you really wanted some precision, a simple bandgap reference and precision resistor would do the job.

Keith

 

[strasni_betmen]

1. From LM317 datasheet I found the circuit that is in the attachement. If I calculate right, the resistor should be >1.2k to get current of about 100uA, but the datasheet specifies that resistor R1 must be between 0.8 and 120Ohm's.

How can I achieve 100uA current?

2. I can't figure out how would I substitute REF200 with LM317 on a dual supply +/- 10V?



King regards

 

[keith1200rs]

I don't think the LM317 is suitable. It has a high current out of the ADJ pin, I believe.

As I mentioned, look at using a bandgap reference and a resistor.

Keith