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HMC980 and HMC637A bias issue

I have used one of the circuits recommended in depl_master_appscircuit_HMC980LP4E-HMC637LP5 document. I am getting -2.4V at Neg out, not current drawn. 

We observe +ve 2.2V at V Gate of HMC980LP4E to  Vgg1 of HMC637ALP5. As I understand this should be negative voltage  to the HMC637 amplifier.

Please let me know solution.

Regards,

Suresh



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[edited by: JValeriani at 8:02 PM (GMT 0) on 9 Oct 2019]
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  • Hi Suresh,

    I'm not sure I fully understand your question.

    It sounds like the charge pump is working because you're seeing -2.4V at the VNEG pin. That means you should be able to get negative voltages on the VGATE output as well. You're saying that you're seeing +2.2V on the VGATE output? What voltage are you seeing on VG2? What voltage are you applying to VDD? What voltage are you seeing on VDRAIN?

    Can you get a scope plot of the turn on when you pull the enable high with all of the above voltages? It would help to figure out where your issue is.

    Also, how are you testing this? On a board you designed, or using two eval boards from ADI? If you're trying to hook two ADI boards together, be sure to use the shortest cables possible.

    Thanks,
    Weston

  • Hello Weston,

     

    We have designed our own boards for testing.

     

    Please find attached the voltage measured at VGate and VNeg.

     

    +12V Supply and +4V for enable and VDig pins has been provided

     

    We are seeing 4V at Vg2 pin.

     

    Concern is  we are seeing +Ve voltage at V gate.

     

     

    Regards,DOCX

  • Hi Suresh,

    Without seeing the schematic for your board design and how you're testing the part, it's very difficult to say why you're having problems. Can you provide a scope plot showing the following lines while triggering on the ENABLE pin going from GND to VDIG?
    - EN
    - VDRAIN
    - VGATE
    - VG2

    What current are you seeing the HMC637 draw? Is it correct, or too high? With a positive voltage on the gate of the HMC637, the pin is way outside the ABSMAX range, so it's possible that the HMC637 is damaged. If not, you should be seeing a huge current draw.

    Is it possible that you have your power supply current limited so that the HMC637 can't draw enough current to satisfy the loop for the HMC980? Maybe the HMC637 isn't able to get current from the supply, so the HMC980 is responding by increasing VGATE to try and satisfy the current.

    Also, the typical value for VGG2 for the HMC637 is 5V. You need to set your resistive divider on the VG2CONT pin to generate about 6.3V.

    Finally, you need to account for the voltage drop across the internal FET of the HMC980 with your VDD voltage. In order to see 12V on the VDRAIN output of the HMC980 at 400mA of current, you need to apply 12.62V to VDD.

    Thanks,
    Weston

Reply
  • Hi Suresh,

    Without seeing the schematic for your board design and how you're testing the part, it's very difficult to say why you're having problems. Can you provide a scope plot showing the following lines while triggering on the ENABLE pin going from GND to VDIG?
    - EN
    - VDRAIN
    - VGATE
    - VG2

    What current are you seeing the HMC637 draw? Is it correct, or too high? With a positive voltage on the gate of the HMC637, the pin is way outside the ABSMAX range, so it's possible that the HMC637 is damaged. If not, you should be seeing a huge current draw.

    Is it possible that you have your power supply current limited so that the HMC637 can't draw enough current to satisfy the loop for the HMC980? Maybe the HMC637 isn't able to get current from the supply, so the HMC980 is responding by increasing VGATE to try and satisfy the current.

    Also, the typical value for VGG2 for the HMC637 is 5V. You need to set your resistive divider on the VG2CONT pin to generate about 6.3V.

    Finally, you need to account for the voltage drop across the internal FET of the HMC980 with your VDD voltage. In order to see 12V on the VDRAIN output of the HMC980 at 400mA of current, you need to apply 12.62V to VDD.

    Thanks,
    Weston

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