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HMC490LP5E Not working as expected

Category: Hardware

Hi there, 

I have a design that uses HMC490LP5E with HMC981LP3E as its controller. I've followed the application example circuit for both parts and on two different boards, I have one that works and one doesn't! I'm trying to figure what could be the problem. The board that works, when probing the VDRAIN and VGATE on the bias control, reads 5V and -1V as expected. However, on the board that doesn't work, both reads near zero. Since both boards have the same circuit design, could it be the HMC490LP5E is sensitive to layout around its VDDs? Below I have two different layout for VDDs. Should the VDDs have separate lines feeding the amp? 

The board that works

That board that doesn't work:

Cheers,

Amin

  • Hello Amin,

    Assuming the active bias controller has had the resistor pods adjusted appropriately to obtain the desired operating IDD and also the Gate voltage is within the HMC490 Absolute rating.

    Then, you are correct. The layout would have a affect on the performance of a board. In your case, the bias voltage for HMC490 has been affected. Looking at your layout that doesn't work, your VDD should have separate line that feed to the amplifier because HMC490 has 3 VDDs.

    Regards,

    Dorant