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LMK05028EVM: Order T06345436, the board with model LMK05028EVM cannot be used

Vivian Sun
Prodigy 90 points

Part Number: LMK05028EVM

Order T06345436
Code D2415497  Model LMK05028EVM  Quantity 1 piece
Customer feedback: The board is not functioning properly. When using the on-board TCXO, JP4 (1, 2 shorted) is connected, JP26 is disconnected, but there is still no signal output; JP26 also needs to be shorted. JP26 is the enable/disable pin for the on-board TCXO.

  • 0
    TI__Genius 17260 points

    Hi Vivian, 

    Can you elaborate more on this issue? The TCXO schematic is shown in Figure 5 of the EVM user guide which documents the functionality of JP4 and JP26. 

  • 0 in reply to Connor Lewis
    Prodigy 90 points

    LMK05028EVM视频.zipLMK05028EVM-TCXO问题.docx
    Hello, regarding the customer's operations and issues, they have been uploaded as an attachment. Please check to see what the cause is and whether a return or exchange is possible.

  • 0 in reply to Vivian Sun
    TI__Genius 17260 points

    Hi Vivian, 

    Thanks for the detailed description here. I've confirmed that with the default TCXO populated on Y2 (7N10070005), the 10MHz output should always be active as long as the TCXO VCC jumper JP4 selects LDO3. For this TCXO the position of JP26 should not have any affect since the the output enable is on pin 8 and not pin 1. 

    Aside from a faulty TCXO, there are a few things that I suspect could be causing issues. In case the SMA connector J12 was overdriven with a high voltage, it's possible that the D11 diodes on the TCXO output were damaged and are causing some kind of short to VDD or GND. With the board powered off, could the customer try measuring the resistance between the R81 resistor and the LDO3 output/GND? If everything is functioning normally this should be high impedance (roughly 1M Ohm on my EVM). Since the TCXO PWR LED lights up on the customer's board I assume the TCXO is getting proper power, but it would also be good to measure this and make sure that it's 3.3V as expected.  

    In case the TCXO is faulty, the simplest solution is most likely to order a replacement board. Do you have an assigned TI sales representative?  If so, they should be able to arrange shipment for a replacement board.