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# INA126: INA126P or other instrumentation amplifier for single supply amplifier of a signal between 0V and 10mV

Part Number: INA126
Other Parts Discussed in Thread: INA122, , INA326

Hi,

I need to amplify a pyrheliometer signal ranging from 0 to 10mv, in the range of an STM32F429ZI ADC that is 0 to 3.3V .

We already have produced some PCB where we have a single 5V supply so INA126P is supplied between 0V and 5V.

Using some resistor I've added 2.5 volt to my signal on Vin and 1.25V to Vref according to following schematics:

It is almost OK, maybe it is still possible to add 4 flying resistors on the PCB, but I've the following questions:

1) why close to zero is not linear

2) how I can determine the transfer function in this case

Best solution for me could be to use an instrumentation amplifier with same pin but that is single supply,

maybe like INA122, but simulating a similar circuit the result is not good and I can't understand why

so, my question is where is my error in this circuit with INA122

and also if you know any other TI instrumentation amplifier that could be suitable for this application.

Thanks,

Antonio

• Concerning previous post:

This is the circuit for INA126

and this is the circuit for INA122

• This instead is INA122 with one of the inputs tied to ground:

and it seems ity is not linear as I need

• Hello Etantonio,

Thank you for your post. The INA126 has an input common mode voltage range which swings beyond the negative rail. On a 5V single supply, the input common mode range is 0 to 3.4V.

However, the INA122 doesn't have this level of swing. It swings 3.75V from either rail. You really can't operate on a 5V single supply with this device for this reason. However, +/-5V would work:

Your input is 0 to 10mV. What is the expected output? I can help see if we can come up with a solution.

-Tamara

• Hi Tamara,

My input is 0 to 10mV and the corresponding output have to be ideally 0 to 3.3V. The supply is a 5V single supply.

This circuit is almost ok, only a reduced dinamic (starting at 1V instead of 0V)

but the real implementation is not tailored to this simulation.

It is available a TI single supply instrumentation amplifier that simply amplify a positive voltage?

Thanks,

Antonio

• Hello Antonio,

No amplifier will be able to output 0V on single supply since there are output limitations on the amplifier. We do have an  instrumentation amplifier called the INA326 which can swing pretty close to 0 on a 5V single supply. I have simulated an input of 0 to 10mV and tracked the output, see below.

The INA is configured in a gain of 300V/V.

Also, find the TINA file attached for your reference.

INA326 0 to 10mV - 0 to 3V.TSC

-Tamara

• Thanks Tamara,

this seems really better than use INA126 as single supply amplifier.

I just modified some values to use the full range of the ADC (0 to 3.3V)

Only problem for me is that INA326 is not available in PDIP package so, at the moment, I need to use an adapter.

Thanks,

Antonio

• Hi Antonio,

My apologies, I shared a schematic that was to 3V out. Looks like you were able to easily modify it to 3.3V, though.

We have a DIP ADAPTER EVM that allows you to convert a VSSOP to PDIP: http://www.ti.com/tool/DIP-ADAPTER-EVM

Would that be helpful for you?

-Tamara

• Thanks Tamara for all your help.

Antonio