POC design

kuo chieh chiu

Prodigy 120 points

Part Number: DS90UB954-Q1
Other Parts Discussed in Thread: DS90UB953-Q1,

Hi team

We use the DS90UB954-Q1 and DS90UB953-Q1 for serdes. DS90UB953-Q1 is TX and DS90UB954-Q1 is RX.

we should provide the power for DS90UB953-Q1 and sensor from RX site.

So we use the POC(Power-over-Coax) method of powering remote sensor systems.

With this method,power is delivered by RX+ trace.

The RX+ trace will become wider.So we can't do 75 ohm impendance control accurately.

1.Does the serdes signal must to do the 75 ohm impedance controlled?

2.what is the funtion of POC(Power-over-Coax)?

3.Can you help to review the schematic? The file is our design schematic now.

over 5 years ago

0 Jiashow Ho over 5 years ago

TI__Genius 11340 points

Hello,

The traces should be 50ohm, not 75ohm. We can tolerate +-10% but if the deviation is more than 10% can cause significant signal reflection. You will need to adjust the stackup to make sure the traces are ~50ohm.

We recommend using the 4G PoC network from the datasheet.

0 kuo chieh chiu over 5 years ago in reply to Jiashow Ho

Prodigy 120 points

Hello

Thank for your answer

We have another question.

1.What are the functions of these two signals(PASS and LOCK)? should we connector to the CPU to monitor the state?

2.The file is our schematic.Do the receive data output design corret?Did it have something risk?

0 kuo chieh chiu over 5 years ago in reply to Jiashow Ho

Prodigy 120 points

Hello

The 4G POC network from datasheet.There are 3 Ferrite Bead in the POC network.

Should we need to add three Ferrite Beads? Can we only add 1 Ferrite Bead?

What value can we choose?

Ferrite Bead, 1500 kΩ at 1 GHz, 0.5 Ω maximum at DC,500 mA at 85°C,This is datasheet value

0 Jiashow Ho over 5 years ago in reply to kuo chieh chiu

TI__Genius 11340 points

Hello,

Regarding the 954 schematics:

- there shouldn't be a decoupling cap on the RX line.

- PDB should have 1.8V pull-up and 10uF to GND. Or it can be simply controlled by the SoC

- Don't put CMC on CSI signals.

LOCK indicates if the the deserializer is able to communicate with the serializer. PASS can be configured for different condition, for example, if the deserializer is receiving 1 - 3 consecutive valid frames.

Ferrite bead changes impedance characteristic based on the current drawn. We suggest adding 3 ferrite beads to keep the impedance high enough. Use the ferrite beads recommended in the datasheet PoC table.

Jiashow

0 kuo chieh chiu over 5 years ago in reply to Jiashow Ho

Prodigy 120 points

Hello

Regarding the 954 schematics:

If we use DS90UB954-Q1 and DS90UB953-Q1 for serdes.

we should use 4G POC network.

why we can't use the 2G POC network?

And when we operate in CSI-2 mode.The deserializer can operate in CSI-2 mode with synchronous back channel reference or non-synchronous mode.

which mode should we choose?

0 Jiashow Ho over 5 years ago in reply to kuo chieh chiu

TI__Genius 11340 points

Hi,

The 2G network is designed to support DVP forward and back channel rates. It's not designed to operate at 4Gbps, which is the forward channel rate when you pair a 953 with a 954.

Synchronous mode is the most widely used case. If there's no other concern, I would suggest this use case.

Best,

Jiashow

0 kuo chieh chiu over 5 years ago in reply to Jiashow Ho

Prodigy 120 points

Hello

We modify the schematic.can you help to review the schematic?

5074.DS90UB954-Q1.pdf

0 Jiashow Ho over 5 years ago in reply to kuo chieh chiu

TI__Genius 11340 points

Hello,

The PoC network looks good now. CMCs shouldn't be used on CSI lanes.

Best,

Jiashow

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