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DS90UB953-Q1: CLK_OUT Resistor Values for IDx

TI Joern
Prodigy 575 points

Part Number: DS90UB953-Q1

Please see the questions below. Thanks in advance.

CLK_OUT/IDX:

For automotive application you need to use lower value resistors because >100 kOhm are not allowed at most of the OEMs. Would be 56 k and 12 k ok?

Best Regards

Joern

  • 0
    TI__Expert 4555 points

    Joern,

    What IDX target voltage are you trying to achieve? There is also a list of recommended values in Section 7.5.1.1 Table 8 of the datasheet:

    www.ti.com/.../ds90ub953-q1.pdf

    Regards,

    Jonny

    Training on FPD-Link Serializer Deserializer devices and system: https://training.ti.com/fpd-link-learning-center

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  • 0 in reply to Jonathan Nguyen
    Prodigy 120 points
    Hi Jonny,

    we want to use IDX=2 with I²C address 0x32 and 1.8 V I²C supply. The resistor values in the data sheet are very high (180 kOhm) and therefore we want to use lower values with the recommended ratio. With 56 kOhm and 12 kOhm we hit ratio of 0.214 very well. Do you see any issues with such smaller values? Is it only because of higher leakage current?

    Thanks and regards,
    Benjamin
  • 0 in reply to Benjamin Peter
    TI__Expert 4555 points
    Hi Benjamin,

    The minimum required load impedance needed is 35k. With the values you suggested, the load impedance is only about 10k.
    At power up, the voltage on the IDX pin is compared to VDD andthe ratio sets various parameters for configuration of the DS90UB953-Q1. Once the DS90UB953-Q1 has beenconfigured, the CLK_OUT/IDX pin switches over to a clock source, intended to provide a reference clock to the
    image sensor.

    Let me come back to this post to provide some further reasoning into why the minimum 35k is needed and potential drawbacks with a lower load impedance.

    Regards,
    Jonny
  • 0 in reply to Jonathan Nguyen
    Prodigy 120 points

    Hi Jonny,

    okay I understand that this high impedance is needed because the pin is multiplexed with clock output. So I think that this might be the reason to keep impedance high to not influence the clock.

    I just saw that this was also written in the data sheet and I missed it. As long as we are not forced to use 0x32 as I²C address the easiest way would be to use IDX 1 because 40.2 kOhm is fine for us.

    Thanks and regards,

    Benjamin