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HMC980LP4E Active Bias Controller VNEG Pin

Category: Hardware
Product Number: HMC980LP4E

I am designing a circuit using HMC980LP4E active bias controller and HMC863ALC4 power amplifier. On the HMC980LP4E, I am using the depletion mode of the amplifier (VNEG = Internal) following figure 34 in the datasheet. I expected VNEG input should be -2.46V as described in table 7 (Mode Selection). But, VNEG is measured as +2.8V. This doesn't make sense. I read both Application note AN-1363 and HMC980LP4E datasheet very carefully, but could not find any clue as to why this is. Could you please give any advice as to what is causing this issue.

  • Hi thyung,

    This is certainly unusual.. If possible, can you give me more detail of your start up and shut down sequencing? As well as the timing between bringing each voltage up? It may also be helpful if you could provide a schematic of your circuit/design..



  • Thank you for your reply.

    I applied externally -2.5V to VNEG. And then I found that VGATE and VDRAIN works correctly when I applied the EN signal. But, still I don't know why the internal negative voltage generator doesn't work.