OPA316-Q1: Please tell me what needs to be done for getting the expected output

Hello Kawasaki-san,

What is connected on the output of the final amplifier?

Also please confirm my below circuit matches the above configuration. I have not place capacitors on the supply pins as this is an ideal simulation, so they are not needed.

Best,
Jerry

Hello Jerry-san,

Thank you very much for your quick reply.

I'm not sure what is connected to the output, but your ideal simulation doesn't show the low voltage like my customer found.  They checked the output voltage on their board using the actual OPA316-Q1 devices.  Their circuit shouldn't violate the datasheet.  Would you please tell me what the root cause would be?  What do you think they should do to have the expected output?  Do they need amplifiers supporting +/- voltage instead of single supply of 5V like this time or current sense amplifiers like INA180-Q1?

Best Regards,

Yoshikazu Kawasaki

Hello Kawasaki-san

I am asking what is connected to the output of the final device to try to determine the root cause, as it is not immediately apparent from just the information you have shared.

Does the customer have the voltage reading from the output of each op amp?

Additionally, if ground is 64mV, the output of the final amplifier should not be able to be below V-. This is why I am asking what is connected to the load, as the op amp should not be able to drive below V-.

Best,
Jerry

Hello Jerry-san,

Thank you for your reply.  The load should be ADC to monitor the voltage from the output of this circuit.  Would you please tell me what the root cause would be?

Best Regards,

Yoshikazu Kawasaki

Kawasaki-san,

My apologies, it appears I am not being specific enough. Can you please tell me all the components that are connected to the output of the amplifier, starting from the amplifier output pin and ending with the ADC input pin. Please list all resistors, capacitors, and other components. A schematic would be most helpful in identifying this.

Additionally, can the customer measure the voltage at the output node of each amplifier in addition to the inputs to the first stage and the final output?

Best,
Jerry

Hello Jerry-san,

I'm sorry that I wasn't understandable enough.  ADC will be directly connected from the final amplifier output without any components like resistors or capacitors.  The outputs of the other amplifiers aren't monitored.  All the connections are shown in the gif file in my first post.  Would you please tell me what the root cause would be?

Best Regards,

Yoshikazu Kawasaki

Hello Jerry-san,

Thank you for you rcomments.  I know it's not possible to drive the external ADC by 26mV.  However your ideal circuit has >2.0V output.  That's why I'm asking what the root cause would be.  You mentioned it could be ground shift or something, but does OPA316-Q1 wolr even if the Vcm=0 or so by Vdd=5V?  Can OPA316-Q1 work such tough conditions?  Don't you have issues like my customer in the past?  What do you need from my customer to find the root cause?

Best Regards,

Yoshikazu Kawasaki

Kawasaki-san,

I am saying that the data provided by the customer cannot be correct.

If the orientation of the current is opposite from what they are expecting, the output would be close to V-. However, the information that has been provided by the customer cannot be true.

This is because this analysis is based on two assumptions. The first is that the customer configured the circuit the same in their schematic as they did in their circuit, and the second is that their measured node voltages are correct. However, if the customer has configured the circuits exactly the same as the above circuit, the second assumption cannot be true.

It is possible that the circuit is configured incorrectly, a device was damaged in some other use case, or that some other error was made, but it is not at all possible for V- of the amplifier to be 64mV, and the output of the amplifier to be 24mV.

I am requesting that the customer check their configuration and remeasure the node voltages. Please request that they measure the output voltage of each amplifier, not just the final amplifier. Also please ask the customer to measure V- at each amplifier pin.

Best,
Jerry