Post Go back to editing

HMC980LP4 External Supply Bias Sequence

Dear Support,

I'm using the HMC980LP4 to bias HMC797AP at 10V and IDSQ=400mA. 

The HMC980 is configured to use the internal VGG generator, and is biased from VDIG=+3.3V and VDD=+10.6V power supplies.  EN is floating.  VG2 is programmed for +3.5V.

I'm following the information found in the HMC980 datasheet suggesting that VDIG be applied first, then VDD.  

I've noticed for the period with ONLY VDIG applied, VGATE goes positive resulting in gate-source junction for the HMC797 (VGG1) being forward biased at +0.6V.  Is this a concern for the HMC797?

Is the VGATE output for the HMC980 current limited?  

Also, does the proper turn-of sequence for the HMC980 follow the opposite sequence?  VDD turned off followed by VDIG?

Thank you.

Parents
  • Hi GeoffcatCPI,

    Yes, the turn off sequence is the opposite of the turn on sequence in the datasheet. I find it peculiar that the Vgg1 is going positive. That would normally not be advised for a product like the HMC797. Does this is happen for a very brief period of time before correcting to the proper negative voltage when the rest of the sequencing is performed? Also, does everything else in respect to the HMC797 look as expected when you fully power up? (Idd, Vgg, Igg, etc..)

    Thanks,

    DanO

Reply
  • Hi GeoffcatCPI,

    Yes, the turn off sequence is the opposite of the turn on sequence in the datasheet. I find it peculiar that the Vgg1 is going positive. That would normally not be advised for a product like the HMC797. Does this is happen for a very brief period of time before correcting to the proper negative voltage when the rest of the sequencing is performed? Also, does everything else in respect to the HMC797 look as expected when you fully power up? (Idd, Vgg, Igg, etc..)

    Thanks,

    DanO

Children