This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Hi,
Good day. I hope you are doing fine.
Our customer is using the LM7321 and they have inquiry about the minimum voltage at IN+ pin. Kindly refer to the inquiry below.
"I know for a power source there is a minimum 2.5+ VDC, but for the signal that it is amplifying which I believe is IN+ on the pin configuration from the datasheet, is there a minimum voltage that should be here? Right now I have .03 VDC here with a gain of 11, but it seems to be only giving me an output voltage of .203 which is around a 6.7 gain"
I hope you could help us with this matter. Thank you for your kind support.
Regards,
Cedrick
Hi Cedrick,
This device is a rail to rail input device meaning that the common mode voltage extends from the negative supply to the positive supply. The common mode voltage for a non-inverting input is equal to the input signal amplitude. The common mode voltage for an inverting amplifier is equal to the voltage at IN+, which is typically a bias voltage or GND.
Please know that the maximum offset voltage of the device is 5mV. So in a gain off 11V/V you can see an error of 55mV at the output. There are other error sources to consider such as input bias current.
Can you please post a schematic so we can take a look at what might be causing the issue?
Thank you,
Tim Claycomb
Cedrick,
Read output voltage for at least two different input voltages. Gain of 11 is dVOUT/dVIN because VOUT = VIN * G + B and we don't really know B.
Be sure to place you negative meter lead at the ground side of the ground resistor like this. Now you will get VOUT = (VIN +Vos) * 11
If the VIN comes from a current sense resistor, check your layout kelvin connection very carefully.
Part Number: LM7321
Hello, I know for a power source there is a minimum 2.5+ VDC, but for the signal that it is amplifying which I believe is IN+ on the pin configuration from the datasheet, is there a minimum voltage that should be here?Right now I have .03 VDC here with a gain of 11, but it seems to be only giving me an output voltage of .203 which is around a 6.7 gain.
I spoke with Cedrick Infantado from Texas Instruments Customer Support who mentioned that the maximum offset voltage of the device is 5mV, so with a gain of 11 it could be an offset of 55 mV, but I am seeing around 130 mV offset on the output. I can provide the schematic for the opamp if it helps.
Hello Shane,
Could you please provide your schematic? That would help me understand your question.
Best,
Jerry