Schematic Design

Hi Dagal, 

I can answer a some of the isolation related questions.

One potential issue is the 5V supply to the ADuM1401 devices on the Raspberry Pi side. The input/ouput pins of the ADuM1401 will scale to the supply voltage fed to the local VDDx pin. The Raspberry Pi B+ operates at 3.3V. As connected right now, the inputs are receiving 3.3V logic while their VIH/VIL levels are scaled for 5V. The isolators on the raspberry pi side need to be supplied with 3.3V. My recommendation would be to supply them from the 3.3V pin on the Raspberry pi header.

Note if 5V outputs from the isolators were connected, they would potentially kill the Raspberry Pi which can only accept 3.3V. I have personally lost a Raspberry Pi connecting I/O pins to 5V mistakenly.

The ADuM1401 has only directional channels with push-pull outputs. I2C requires at least a bidirectional channel on the SDA line for ACK bits and any data to come back to the Raspberry Pi. I2C also needs devices attached to the bus be open collector outputs to avoid contention. You can create glue logic to bind a forward and reverse channel of the ADuM1401, but my recommendation would be to pick an I2C isolator.

Can you provide a part number for the 5V/5V DC converter? Is it a galvanically isolated device?

Thanks,

Jason    

Hello Jason,

First of all, thank you very much for your response. I appreciate the note about the potential issue, and I was aware of it from the beginning. However, I believe my circuit is correct in this regard. Please correct me if I am mistaken.

One potential issue is the 5V supply to the ADuM1401 devices on the Raspberry Pi side. The input/ouput pins of the ADuM1401 will scale to the supply voltage fed to the local VDDx pin.

In general, I use 3.3V for the supply of the ADE7878 and the two sides of the isolators. Please note that the two sides are potentially separated by a DC-DC converter. Additionally, I supply the Raspberry Pi with 5V.

The Raspberry Pi B+ operates at 3.3V. As connected right now, the inputs are receiving 3.3V logic while their VIH/VIL levels are scaled for 5V. The isolators on the raspberry pi side need to be supplied with 3.3V. My recommendation would be to supply them from the 3.3V pin on the Raspberry pi header. Note if 5V outputs from the isolators were connected, they would potentially kill the Raspberry Pi which can only accept 3.3V. I have personally lost a Raspberry Pi connecting I/O pins to 5V mistakenly.

The Raspberry Pi 3B+ operates with a 5V supply voltage and is powered by me through the transformer (230V/5VDC) and then through the DC/DC converter for isolation. That is, the supply voltage for the Raspberry Pi is 5V. The isolators are then supplied with 3.3V through another converter (5V/3.3V). That is, the supply of the isolators is 3.3V.
On one side, the ADE7878 and the left side of the isolators are powered. The same happens on the right side. However, the two sides (right and left) are separated by a DC-DC converter. The DC-DC converter (RKE-0505S_H) ensures a potential separation of these two sides.

The ADuM1401 has only directional channels with push-pull outputs. I2C requires at least a bidirectional channel on the SDA line for ACK bits and any data to come back to the Raspberry Pi. I2C also needs devices attached to the bus be open collector outputs to avoid contention. You can create glue logic to bind a forward and reverse channel of the ADuM1401, but my recommendation would be to pick an I2C isolator.
I have now modified the component to (ADUM2250) and the schematic (see attachment). This will allow a bidirectional communication using the I2C.

Can you provide a part number for the 5V/5V DC converter? Is it a galvanically isolated device?

I use the DC-DC converter (RKE-0505S_H). 

Once again, thank you for your help and the comments. I look forward to your feedback.

Dagal