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AFE4490: AFE4490

Part Number: AFE4490
Other Parts Discussed in Thread: LMV112

Hi ,

We are using AFE4490 IC in our design.We are facing difficulty in passing Radiated emission test.

We have three boards in the design. The Main board with processor , AFE board with two AFE4490 IC's and LED board . The AFE board is connected to processor board with a FPC flex cable.

In AFE baord ,we are using a single 8MHz Oscillator with a clock buffer LMV112 for feeding clock for both AFE's . 

In Radiated emission test , we are seeing a pattern of narrow band emission repeating exactly at 8MHz . The unit emissions crossing the limit in the band 200MHz to 500MHz . We found that the problem area is AFE board by some experiments . The Processor board operating alone has no issues . 

 We observed improvement around 5dB when the LED board is disconnected from the AFE board .  My questions are as follows 

1) AFE board is realized with 2 layer PCB - Is this OK ?

2) We are connecting LED with common Anode push pull configuration , There is no Series resistor for LED . In this case do we need supply pin 17 and pin 18 with 5V ? 

Please suggest any key hardware checks and software settings we need to do to reduce emissions from the board .

Let me know if you need more information. 

  • Hi Dilip,

    Let me check with design team and get back to you by early next week.

  • Hi Dilip,

    Here are few answers as well as comments regarding your issue.
    1) 2 layer PCB should be OK.
    2) As long as you have external 5V supply at anodes of LED, there shouldn't be a problem.
    3) Is the 8MHz emission happening from AFE or "clock buffer + oscillator " . What if you disconnect the buffer from the AFE and do the test?
    4) Did you try pulling AFE_PDN pin LOW and doing the test?
    5) Can you bypass the buffer and give the oscillator's output to AFEs and repeat the test?

  • Hi Prabin ,

    Thank you for the response .

    We tried several iterations with AFE_PDN low , directly feeding the clock , using coaxial cable etc .
    There are some stubs on the board with 8MHz , since we are using a single oscillator to two AFE chip sets .
    The SPI also runs at 8MHz . We are now going with layout change with 4 layer PCB and 50Ohm traces for clock signals.

    Need support in schematics and Layout review from TI .

    Will you be supporting the review .
  • Hi Dilip,

    Since we are already engaged with you guys directly over email, I am closing this thread.
    Yes, you can directly send us the schematics for review.