ISO7241M: Output waveform of isolator is DC shifted

Hi Sujay,

To better understand the system and issue, please share below details

• Is this issue observed on all channels? or on a specific channel?
• In the attached waveform the channel 3 scale is 50V, what is it connected to? where are the inputs and outputs of the Isolator connected to? can you please share some more information about the system.

Regards

Tejas

Hi Tejas,

• Is this issue observed on all channels? or on a specific channel? - Yes this isuue is observed in all the channels of digital isolators in the boards
• In the attached waveform the channel 3 scale is 50V, what is it connected to? . -Channel 3 scale is 50V due to attention settings were wrongly made. 
• where are the inputs and outputs of the Isolator connected to? - Input is connected to a ADC IC adcs7476 and output of isolator is connected to microcontroller
• can you please share some more information about the system-  Please refer the Schematics attached pH Sensor1.pdf

Regards

Sujay A

Hi Sujay,

Thanks for the information.

In the scope waveform attached, I assume the digital isolator output is measured at Sensor_SIN and the input is measured at DO_PH. Please correct me if my understanding wrong.
If yes, are there other nodes on this line and is there any pull up resistor on this line?

Is it possible to disconnect the isolator output being routed to MCU/ADCS7476 and capture the output waveform at the IC pin. This will help us to understand if the DC offset is introduced by ISO7241.

Regards
Tejas

Hi Tejas,

You are right, Output is measure at Sensor_SIN (Blue waveform) and input measured at DO_PH (Pink waveform)

This line doesn't have any pull-ups.

Is it possible to disconnect the isolator output being routed to MCU/ADCS7476 and capture the output waveform at the IC pin. This will help us to understand if the DC offset is introduced by ISO7241 --->As there are no jumpers connected between the outputs and inputs of the isolator, it would be difficult to isolate the output. We will try for it.

Please let me know if you have any suggestions.

Regards

Sujay A

Hi Tejas,

We have tested the ISO7421 seperately (isolating it from controller)

Made external circuit with ISO7421M and provided inputs as below

Input (pin 11) :Connected to Isolated Ground, i.e Low

EN1 /EN2 : Checked both Open and High

Output Pin: 6: (monitored w.r.t DGND , output side ground) ; Measured 4.09 V

But as per datasheet for Low Input, output should also be Low-

We were unable to get the output as mentioned in datasheet for IN=L then OUT=L.

Require your help on this.

Regards

Sujay A

Hi Sujay,

This is NOT expected behavior from our device. The ICs are extensively tested before shipping out. Can you please redo the previous experiment with a fresh IC.

Regards

Tejas

Hi Tejas,

We are using 4 digital isolators on the board,

We had checked at all the outputs of 4 IC's , we are getting same output (4.09V) for LOW input.
We had also checked on a fresh board and components newly populated - But still the same.

Regards
Sujay A