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HMC980 vs HMC981

Category: Hardware
Product Number: HMC980; HMC981


I am doing some DC tests using an Electronic Load on HMC980 and HMC981 DevBoards, an I'm having different results.


  • Does not matter what sequence VDIG and VDD are applied. It just works.
  • EN pin enables and disables VDRAIN and VGATE as intended, and does not cause it to latch.


  • VDIG needs to be turned on AFTER VDD, contrary to graph in datasheet.
  • When disabling the ABC using the EN pin it latches off, requiring power cycle of VDIG.

Would you know why this difference in the power up sequence and EN pin behaviour?


Mateus Ohse 

  • Hi Mateus Ohse ,

    The startup sequence illustrated in the datasheet should be followed to avoid damage to the ABC. The reverse order should be followed to power down the ABC. Can I ask why you are testing the ABC in this way? What is your end application?



  • Hi Dan,

    With the HMC980, what I am experiencing is that if I follow the power-up sequence from the datasheet, it does not start:

    I actually have to apply VDD prior to VDIG for it to start.

    And then looking at HMC981 datasheet, the Power-up waveform is VDD first and then VDIG:

    And also, the EN pin on HMC980, is causing it to latch, while it's working as indented on HMC981.

    Can I ask why you are testing the ABC in this way? What is your end application?

    Just doing some basic DC bench checks, before I connect it to an amplifier.


  • I would suggest connecting the ABC to an amp and following the recommended bias sequencing.. I suspect that the bias sequencing will work with an active amplifier in line (remember to reverse for power down).