Low Power Opamp for ADC 1.8V

Hello,

Please take a look at the TLV9062. If the TLV9062 does not work for you please provide us with more information on your op amp requirements. Please provide the channel count, package, bandwidth, offset voltage, input bias current, slew rate, etc. requirement for your design.

Thank you,

Tim Claycomb

Hi Tim Claycomb
After research I decided choose ADS1248 for RTD sensor( PT1000 3 wire), LMP91200 for PH sensor, and LM358 for pressure sensor
However, I want to find a replacement for LMP91200 because it's output is analog, can not have digital port (SPI/I2C) for readout data
So, can you suggest a suitable part for me in this case?
And for pressure sensor?

www.bingo-sensor.com/.../Industrial_Pressure_Sensor_PT-ID016.html
Thanks

Hello,

The LM358 has a minimum supply voltage of 3V, therefore it will not meet your 1.8V supply voltage requirement. Will the TLV9062 not work for your application?

The LMP91200 is supported by another team here at TI. I recommend creating another forum post for the LMP91200 to see if they have a recommended replacement for the LMP91200.

It is difficult to make a recommendation for a pressure sensor because it is very dependent on your requirements. Cost, accuracy, supply voltage, supply current, etc. The only potential issue I saw with using the pressure sensor you linked to is that it can output 0.5V to 4.5V. If the amplifier is on a 1.8V supply and the pressure sensor outputs 4.5V it is possible for the output of the pressure sensor to damage the device depending on the circuit configuration.

Thank you,

Tim Claycomb

Hi
I have change to try design with TLV9062
Can you have any suggest for this?
Thanks

Hello,

There is one concern I have with the design. With a supply voltage of 5V the output can only swing from approximately 15mV to 4.985V. Since the design uses an inverting amplifier, if the input is positive the output will try to go below 0V which cannot happen because the output limitation of the device. Is it possible to have both amplifiers in a non-inverting configuration? Please see out TI Precision Lab Videos on Input/Output Limitations for more information.

I recommend putting your design into TINA-TI to verify it will perform the way you are expecting.

Additionally, I recommend using the Analog Engineer's Calculator for help sizing the RC filter at the input to the ADC.

Thank you,

Tim Claycomb

Hi Timothy Claycomb
After tried with TI amplifier design tool, I have just choose new part for ORP and Pressure sensor
Can you give me any suggest?

Hello,

If the ORP sensor output voltage will not go beyond +/-3V then the LM833 will likely work just fine. If it will go beyong +/-3V I do not recommend using the LM833 due to the input common mode range of the device. The input common mode range is specified 2V from each rail which means in the current configuration the input of the first amplifier (the buffer) can only have an input between -3V and 3V.

The LMP2022 should also work for the design if the pressure sensor output voltage does not output less than -0.2V or more than 4.2V. Again this limitation is due to the common mode range of the device.

I recommend putting your design into TINA-TI to verify the design will operate the way you would like.

Thank you,

Tim Claycomb

Hello,

One additional thing, I recommend increasing the resistors in the feedback of the LMP2022 by 10x. Having low values resistors in the feedback will increase the current consumption of the design. It may also limit the output swing of the amplifier because the amplifier will be required to output large amounts of current. For more information on output swing limitations of amplifiers I recommend watching our TI Precision Lab videos on Input and Output Limitations.

Thank you,

Tim Claycomb

Hi Tim Claycomb
Thanks for your suggestion about my circuit.
Really I tried simulation by TINA Tool and resut show which i expect
But in case sensor is disconnect, the output will swing over maximum of ADC limit( 0->1.8V)
So, I add 10K pull down for all input of first each opamp block
Can you suggest for best solutions in this case?
Thanks

Hello,

When the sensor is disconnected the 10k pull down resistor will ground the input of the op amp which will force the output to get as close to ground as it can get.

This should not be an issue with the LM833 because you are using +/-5V supply.

However, the LMP2022 is only using a single supply (+5V and ground) so the output will never be able to get to ground, due to the output swing limitation. Also, when the sensor is reconnected it will take some time for the amplifier to transition off of ground due to overload recovery of the device. But the overload recovery may not be a concern in your design.

Another solution to prevent damaging the input to the ADC is to add diodes to the output of the amplifier.

Thank you,

Tim Claycomb

Hi Tim Claycomb 
Can you tell me more detail with output diode?
maybe use clamp diode for output?
Thanks

Hello,

Please watch our TI Precision Lab Videos on Electrical Overstress (EOS) for more information. The first video discusses relevant information on connecting diodes on the output. While the videos discuss connecting diodes on the output to protect the amplifier the idea is the same to protect the ADC input.

Thank you,

Tim Claycomb

Hi Tim Claycomb
I tried with clamp diode output but dont have a result
Now, I choose connect an input with resitor 10K to ground to set opamp off when disconnect with sensor
Maybe I will test on testboard first
Thanks