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Original question:

DS90UB933-Q1: DS90UB933 with DS90UB954

DS90UB933-Q1: 933/934 EMI issue(157.25MHz 3.2dB; 188.71MHz 7.5dB)

Amelie Zheng
Genius 10865 points
Part Number: DS90UB933-Q1

Hi Team,

My customer use 933/934 and met EMI issue.

  • 157.25MHz: over 3.2dB
  • 188.7MHz: over 7.5dB

Because PCLK=62.9M,so 188.7MHz is because three times of PCLK.

Because when power off 933, 157.25MHz is disapper, so 157.25MHz is because of 933.

Any advice about fix out 157.25MHz and 188.7MHz?Thanks!

1) 933 and 934 both  work

you can see:

  • 157.25MHz: over 3.2dB (compare to margin)
  • 188.7MHz: over 7.5dB (compare to margin)

2) 933 off, only 934 work

3) 934 off, only 933 work

  • 0
    TI__Guru* 83600 points

    Hello Amelie,

    which clocking mode are you using, PCLK or External CLK?

    Which Mode are you using, 10-bit, 12-bit HF or 10-bit LF?

    You know EMI is a system issue not a device issue, so we may need to review your schematics and Layout!!

  • 0 in reply to Hamzeh Jaradat
    TI__Genius 10865 points

    Hi Hamzeh,

    Thanks for your reply.

    I total agree with you that it is a system issue. And I will ask the customer about the configuration and SCH/PCB as you mentioned before.

    May I ask:

    • Instead of changing PCB, are there other method customer can try first based on your experience? Such as add caps/CML in DOUT...If you can recommend some typical methods, customer can try first and if it doesn't work, we can just review SCH/PCB and ask them to change...

    • What kind of reasons do you think the 157.25MHz come from? When power off 933 ,157.25MHz disappear... I don't know what kind of signal from 933 will lead to 157.25MHz...

    Many thanks again for your help!

  • 0 in reply to Hamzeh Jaradat
    TI__Genius 10865 points

    Hi Hamzeh,

    Please see my feedback below:

    which clocking mode are you using, PCLK or External CLK?

    External CLK, SOC generate PCLK to 933.

    Which Mode are you using, 10-bit, 12-bit HF or 10-bit LF?

    10 BIT

    May I ask:

    • What kind of reasons do you think the 157.25MHz come from? When power off 933 ,157.25MHz disappear... I don't know what kind of signal from 933 will lead to 157.25MHz...

    Thanks!

  • 0 in reply to Amelie Zheng
    TI__Guru* 83600 points

    Hello Amilie,

    When using the 10-bit mode, the PCLK is divided by 2, hence the resulting frequency is 62.9MHz /2 = 31.45MHz. If you multiply this frequency x5 = 157.25MHz.

    You may ask them to reduce the VOD as following: 

    • Write in REG 0x04[7:6] the value 0b’01. (Default = 0b’10)

  • 0 in reply to Hamzeh Jaradat
    TI__Genius 10865 points

    Thanks a lot! 

    It really helps!