DS90UB635-Q1: Can the serializer be configured through FPD-Link? Can the FPD-Link signal be isolated with HV caps or transformer?

Hello John,

Thank you for your questions. Please find feedback below.

1. Yes, the serializer can be programmed remotely from a controller on the deserializer side. You will just need to make sure that the proper I2C addresses are being used for  each device on the bus. This app note has some examples that may be helpful. Section 3.1.2 details the remote serializer scenario specifically.
   
   
2. Are you asking about adding isolation between the serializer and the deserializer? We don't normally recommend connecting anything between the devices on the FPD-link signal other than the required AC coupling capacitors. Is there a reason the isolation barrier can't be placed prior to or after the FPD-Link devices?

Regards,
Darrah

Hi Darrah,

Thank you for reply.

Yes, I am considering to add isolation between the serializer and deserializer. As you said, FPD-link signal can be AC coupled, so I am thinking maybe it is possible to implement isolation with HV caps.

The reason why cannot do isolation on MIPI CSI interface is that there is not suitable MIPI isolation device. LVDS device can only support up to 150Mbps.

Thank you!

John

Hi John,

When you say implement isolation with HV caps, do you mean use capacitors with a higher voltage rating for the AC coupled capacitors? As long as the appropriate capacitance values are being used as specified in the datasheet, it is okay to use capacitors with a higher rating. Opto-couplers have been used in some systems to achieve isolation between the serializer and deserializer before, however with this kind of configuration the back channel would need to be disabled. Care also needs to be taken to ensure that all channel specs are still being followed and there is no negative influence on the signal when making modifications to the channel configuration. Could you provide more details on your system and explain why 4kV/50Hz isolation is needed on the FPD-Link channel? The context will be useful since isolation is not commonly needed in FPD-Link systems.

Hi Darrah,

It is interesting. Opto-couplers can be used between serializer and deserializer? 

The reason why isolation is due to the application is medical endoscope. The imaging sensor will contact human boardy directly. So the imaging sensor should be isolated from main system to protect patient. It is required by related industrial standard. (4kVrms/50Hz, 60s).

Thank you!

John

Hi John,

Opto-couplers have been used before for special cases, but like I mentioned the back channel would have to be disabled, which is not exactly how FPD-Link is intended to operate.  The deserializer would not be able to communicate with the serializer in this situation and there would be a break in I2C communication so the deserializer would not be able to communicate with any other devices on that half of the I2C bus or pass on I2C transactions. Communication and data transmission would only be able to go in one direction.

Is the FPD-Link interface the only feasible location to place the isolation barrier? Are there other places in the system where the isolation barrier could be placed? Increasing the voltage rating of the AC coupling capacitors would be a more straightforward and reliable method.

Hi Darrah,

Isolation in other location is difficult. The signal chain is: MIPI CSI signal from image sensor --> DS90UB635 --> DS90UB63X --> processor --> display. Isolation in PFD-Link is the most convenient way.

I checked the AC coupling capacitance. The capacitance is too high to be used for HV AC isolation. Do you have any other idea?

Thank you!

John