HMC465LP5 Biased with HMC981

We are using the HMC465LP5 in our application; the bias to the device is provided by the HMC981 as per the recommended application circuit in the HMC981 datasheet.

We have noted that when the HMC465 bias is OFF (e.g. EN=0 on the HMC981), the gate voltage VGG1 on the HMC465 is ~ -2.5V; this is Vneg on the HMC981.

However, the datasheet for the HMC465LP5 states that the maximum range for VGG1 is -2V to 0V (see page 8-4 of the HMC465 datasheet, Absolute Maximum Ratings).

Should we be concerned that the -2.5V is applied to VGG1?  The two datasheets seem to contradict each other.

  • 0
    •  Analog Employees 
    on Oct 7, 2016 8:16 PM

    Hi rasmith,

    I will look into whether or not there is any margin on the HMC465LP5 Vgg1 pin's AMR.

    I will also ask our ABC apps engineer what changes would be required to the HMC981 app circuit in order to limit the voltage swing at the Vgg1 pin.

    Regards,

    SMcBride

  • 0
    •  Analog Employees 
    on Oct 7, 2016 8:21 PM

    Hi rasmith,

    You can change the Vgate threshold level of HMC981 from -2.5 to -2 V.

    We have an application note on active bias controllers, AN-1363. On the application note, there is a section addressing this. Please refer to AN-1363 for further details on adjusting the Vgate threshold value.

    Best,

    Kagan

  • Kagan:

    Thanks for the information.  I have read AN-1363, and I have modified a circuit to make change the Vgate voltage as recommended in the Application Note.

    However, we have multiple circuit cards already designed with the HMC981 and the following amplifiers: HMC460, HMC463 and HMC465.  All these devices have Vgate between -2V and 0V.    This results in the following questions:

    What are the implications if we don't change the circuit to limit the Vgate voltage to -2V?  

    What is the impact on the devices if the minimum value of Vgate is -2.5V instead of -2V during power-up?

    Will repeated application of -2.5V during power up cause any reliability issues with the amplifiers?

    Thanks for help with this.


    Regards

    Russell

  • 0
    •  Analog Employees 
    on Oct 18, 2016 7:38 PM

    Hi Russell,

    Formally, we would advise you to ensure that your operating voltages adhere to the AMR values shown in the data sheet. That said, if you are unable to change your circuits such that they operate in compliance with the AMR values then I can try to consult with Design to gain a better understanding of what risks may be at hand. However, due to their workload there is no guarantee that I will be able to obtain answers...and those answers would be for insight only and would not be guaranteed. It's my educated guess that the Vgg1 AMR ratings are based upon the drain-to-gate breakdown voltage ratings for the specific wafer fabrication processes used for the die involved. Accordingly, the Vgg1 voltage limit (for quiescent conditions, at least) would likely depend upon your Vdd voltage conditions. If you can tell me your Vdd voltage conditions for each part then I will ask Design for their comment.

    Regards,

    SMcBride

  • Fro the parts I mentioned above, we are using the following drain bias voltages:

    HMC460: Vdrain=8V (Vdd into HMC981 =8.8V)

    HMC463: Vdrain=5V (Vdd into HMC981 = 5.6V)

    HMC465: Vdrain=8V (Vdd into HMC981 = 8.8V)

    Let me know if you need any more information before sending my questions off to the design department.

    Regards

    Russell