INA240: Adjustable gain CSA or shared sense resistor for two CSAs

bob young

Part Number: INA240
Other Parts Discussed in Thread: INA185, , INA225

I have an application where I need 100V/V gain for currents up to 20A and need reduced gain for currents above that level to avoid saturating my ADC. I haven't located any dual gain or reconfigurable gain current sense amplifiers (CSAs). If they do exist and are available please point me to them. Alternatively, I may try sharing one sense resistor and adding a second low gain CSA from the same family for the extreme current case. Would this work well?

over 3 years ago

0 Peter Iliya over 3 years ago

TI__Mastermind 32395 points

Hello valued engineer,

This could work. Another option is this circuit, which uses an instrumentation amplifier:

https://www.ti.com/lit/an/sboa529/sboa529.pdf?ts=1649826410163&ref_url=https%253A%252F%252Fwww.google.com%252F

Here is another circuit, but it would require changing gain by changing a resistance in Rset, usually done similar to the circuit above and use a FET to open and close another parallel resistive branch.

https://www.ti.com/tool/CIRCUIT060036

Hope this helps.

Best,

Peter

0 bob young over 3 years ago in reply to Peter Iliya

Prodigy 85 points

Thanks for the tips on the instrumentation amplifier technique. Unfortunately, that device is currently unavailable. The other CSA is interesting although I would have to float the ground to use it in my application because the part is limited to about half the voltage I need to work with. Both solutions are helpful in a general sense. Thanks for the ideas! For now, I will use the CSAs in parallel to handle my wide current dynamic range.

0 Peter Iliya over 3 years ago in reply to bob young

TI__Mastermind 32395 points

Hey Bob,

Please know that the second circuit I sent can use just about any bidirectional current sense amplifier, thus you could use the INA240 in the second circuit. It is not just limited to the INA185. Here is an example of this.

https://www.ti.com.cn/cn/lit/an/sboa513/sboa513.pdf

Best,

Peter

0 Peter Iliya over 3 years ago in reply to Peter Iliya

TI__Mastermind 32395 points

Hey Bob,

I forgot to mention that we have the INA225 which is a programmable gain CSA so gain can be dynamically changed.

Best,

Peter

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INA240: Adjustable gain CSA or shared sense resistor for two CSAs