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DS90UB953-Q1: Request 953 Circuit Review

choi donghun
Prodigy 100 points
Part Number: DS90UB953-Q1

Hello, I am an engineer working for a company called Patron in Korea.
I'd like to ask for a circuit review of TI.

I attached the PDF


#Specifications used
-. Using MIPI 4 Lane
-. I2C Voltage 1.8V
-. Non-Synchronous AON Mode(MODE3)

#Questions
-. Overall circuit modifications
-. RC value of PDB pin

The current POC current is expected to be 260 mA/6.5 V. Is this possible?
Could you suggest the POC current value that your company recommends?

  • 0
    TI__Mastermind 28380 points

    Hi Choi,

    I can perform a Schematic Review. But I don't see a PDF attached. Could you try to post the PDF again?

    The RC value of the PDB pin require a 10-kOhm pull-up resistor to 1.8V and a capacitor to GND that is at least 10uF. And the impedance characteristics of the ferrite beads in the PoC circuit deviates with the bias current. If you use the suggested components listed in the datasheet for the PoC circuit, then we recommend the current to be less than 150mA. See section 8.1.1 Power-over-Coax in the 953 datasheet for more details.

    Best,

    Justin Phan

  • 0 in reply to Justin Phan
    Prodigy 100 points

    I'm sorry. I missed the attachment. Could you go over it again? Do you have any POC combinations recommended by TI to use more than 200mA?

    TI_DR_953.pdf

  • 0 in reply to Justin Phan
    Prodigy 100 points

    Also, I understand that inductors in this POC line allow up to 500mA, but I would like to know why TI limits the current of 150mA.

  • 0 in reply to choi donghun
    TI__Mastermind 28380 points

    Hi Choi,

    The timeline for a Schematic Review is roughly one week. I will return with comments within the next few days (7/16 at the latest).

    And the recommended "4G" PoC Network for the 953 is in the 953's datasheet. This PoC circuit is used when your 953 is operating in Synchronous Mode and has a Forward Channel Line Rate of about 4Gbps. While it is necessary for PoC current to be less than the rated current of the PoC filter components, there are a number of reasons why we recommend a much lower current of <150mA through the recommended "4G" PoC circuit.

    1. The current draw multiplied by the DC resistance of the cable and PoC filters will translate into noise that can affect the signal integrity and EMI. Since the power is fixed, we recommend having a lower current and higher voltage in order to have less noise on the FPD-Link channel.
    2. We recommend sending a higher voltage (>10V) over the COAX cable and then using a high-efficiency voltage regulator to drop the voltage to the required levels.
    3. Channel specifications, such as Return Loss or Insertion Loss, are easier to meet with lower current.
    4. In most Ferrite Bead datasheets, the manufacturers only specify the parameters of the bead at zero DC bias current. However, when these ferrite beads are used for power supply filtering, the load current going through the beads is never zero. And as the DC bias current increases from zero, the parameters of the Ferrite Bead can drastically change. For effective power supply noise filtering, a general rule of thumb is that you should use ~20% of the rated current for the Ferrite Bead. But the 953 datasheet specifies that the recommended "4G" PoC circuit can work effectively with a PoC current of <150mA.
    5. You can refer to this App Note for more information on PoC design with the 953: https://www.ti.com/lit/an/snla272/snla272.pdf?ts=1626106697928&ref_url=https%253A%252F%252Fwww.google.com%252F

    I will also need to do some digging to see if we have any recommended PoC circuits that can support more than 200mA and work with the UB953. I will get back to you on this.

    Best,

    Justin Phan

  • +1 in reply to Justin Phan
    TI__Mastermind 28380 points

    Hi Choi,

    I've completed your Schematic Review. Attached is a PDF with my comments:

    TI_DR_953_Reviewed.pdf

    And for your second question, I would like to reiterate that the "4G" PoC circuit listed in the datasheet is our recommended solution for the UB953, when it runs at a Forward Channel line rate of about 4Gbps with the UB954/UB960 deserializers. The recommended PoC current is less than 150mA.

    I recommend that you increase the DC voltage in your application and lower the current requirement. And then use high efficiency voltage regulators at the destination to bring the PoC voltage to the required levels. The lower current will result in less noise over the cable and help with meeting the channel loss requirements. 

    Best,

    Justin Phan