Problems when using HMC980LP4E eval board with HMC487LP5 eval board

I have a HMC487LP5E (PA) evaluation board. When I use an adjustable voltage supply and follow the application note on how to bias the PA it works perfectly and draws the expected 1300 mA with a gate voltage of appoximately -0.2 V and a 7 V drain voltage.

When I try to use the Active Bias Control (ABC) HMC980LP4E to supply the PA it does not work. When the ABC is not connected to the PA it gives out a drain voltage when enabled and a positive gate voltage (2.5 V). When it is unconnected and disabled the drain voltage is 0 V and the gate voltage is -2.5 V (as expected). When the PA is connected and the ABC is enabled VDRAIN is 0 V and VGATE is -0.7 V. I have tried adjusting RSENSE (R10 potentiometer). I have tried with S1=VDIG and S0=VDIG which would require a VDD of 7.9 V according to Table 1 in the datasheet of the ABC. I have also tried with S1=VDIG and S0=GND with a VDD of 8.1 V as given in Table 3 of the datasheet of the ABC for the HMC487 PA.

ALM is low in all cases and TRIGOUT is also low. Any suggestions on how I can find out what I am doing wrong?

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  • Hi,

    Yes that was also my impression that the parts work separately. I am using the ADI EVB (both for HMC487 and HMC980). I will attach a photo of the connections.

    I tried adding R5=270K and R7=180K (available values). Should I try other values? Or what do you mean by tweaking the resistor values? Everything else is connected as in your picture of the schematic.

    I get these voltages now:

    Unconnected and enabled HMC980 (VDIG=3.6 V, EN=3.6 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=8.1 V

    VGATE=4.16 V

    Unconnected and disabled HMC980 (VDIG=3.6 V, EN=0 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=0.0 V

    VGATE=-0.88 V

    Connected to HMC487 and enabled HMC980 (VDIG=3.6 V, EN=3.6 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=0.0 V

    VGATE=-0.001 V

    Connected to HMC487 and disabled HMC980 (VDIG=3.6 V, EN=0 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=0.0 V

    VGATE=-0.008 V

    I have tested the AMP by itself and saved the log of Vgate, Idd and Igate. The log is attached.

Reply
  • Hi,

    Yes that was also my impression that the parts work separately. I am using the ADI EVB (both for HMC487 and HMC980). I will attach a photo of the connections.

    I tried adding R5=270K and R7=180K (available values). Should I try other values? Or what do you mean by tweaking the resistor values? Everything else is connected as in your picture of the schematic.

    I get these voltages now:

    Unconnected and enabled HMC980 (VDIG=3.6 V, EN=3.6 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=8.1 V

    VGATE=4.16 V

    Unconnected and disabled HMC980 (VDIG=3.6 V, EN=0 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=0.0 V

    VGATE=-0.88 V

    Connected to HMC487 and enabled HMC980 (VDIG=3.6 V, EN=3.6 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=0.0 V

    VGATE=-0.001 V

    Connected to HMC487 and disabled HMC980 (VDIG=3.6 V, EN=0 V, S0=3.6 V, S1=0 V):

    VDD=8.1 V

    VDRAIN=0.0 V

    VGATE=-0.008 V

    I have tested the AMP by itself and saved the log of Vgate, Idd and Igate. The log is attached.

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