• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 33 subscribers
  • Views 429 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

DS90UB960-Q1: TVS

DS90UB960-Q1: VPOC noise

Zehui Li
Intellectual 540 points
Part Number: DS90UB960-Q1


Hi,

     Here is a description from Datasheet Page166.     

     "The VPOC noise must be kept to 10 mVp-p or lower on the source / deserializer side of the system. The VPOC fluctuations on the serializer side, caused by the sensor's transient current draw and the DC resistance of cables and PoC components, must be kept at minimum as well. Increasing the VPOC voltage and adding extra decoupling capacitance (> 10 µF) help reduce the amplitude and slew rate of the VPOC fluctuations."

    When we talk about "noise", do we refer to the absolute Vpp of VPOC including the regulator output ripple and load transient  and so on? What is the measure condition?

    BTW, I read datasheets of other devices, and they define "VPOC" as the input voltage of regulator after POC on the serializer board. And Rin+ noise is required 10mVp-p max. Does DS90UB960-Q1 has the similar requirement?

  • 0
    TI__Mastermind 28420 points

    Hello,

    Thank you for your question. We are currently working on updating many of our datasheets and application notes so there may be some differences in the exact wording used across documents currently. When talking about noise regarding the POC network there are two main types/locations. For the purpose of this post I'll refer to the two as VPOC noise and RIN+ noise. VPOC noise is the noise seen on the serializer side of the link and  RIN+ noise is the noise seen on the deserializer side of the link. The image below shows the measurement nodes/locations in context of the entire FPD-Link system.

    VPOC noise comes from the serializer and sensor operation and is measured at the input of the DC regulators. When measuring VPOC noise, you can expect a waveform similar to the image below. The supply noise comes from the switching of the regulators and the pulses are due to the varying current draw of the sensor (periods of transmitting active video data vs blanking data). The requirements for VPOC noise are:

    • VPOC supply noise less than 100mV peak-to-peak
    • VPOC pulse less than 500mV peak-to-peak
    • VPOC pulse slew rate greater than 200μs/V

    RIN+ noise is the noise that is seen at the input of the RIN+ pin of the deserializer. A large amount of noise on the RIN+ pin can result in degradation of the FPD-Link signal. The RIN+ noise must be less than 10mV peak-to-peak between 0 and 50MHz.

    Regards,
    Darrah

  • 0 in reply to Darrah Merillat
    Intellectual 540 points

    Hi Darrah,

         About VPOC, the pulse is caused by changing current and DC resistance of the whole channel. Do you have any recommendation about the DC resistance limit of the whole channel or the PCB？

  • 0 in reply to Zehui Li
    TI__Mastermind 28420 points

    Hello,

    Please reach out to your local TI sales representative to request the FPD-Link channel specifications documentation.