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Help needed for HMC183QS24

I had 2 HMC183QS24 used in a 8 channel switched filter bank. The 2 HMC183 are mirrored and the TLL inputs are synchronized by a CD74HCT04PWR (Hex inverter by Texas Instrument).

At first, the system works fine. However, the HMC183 suddenly fails as the 2 HMC183 switches are no longer synchronized (seems like the A B C pin of HMC183 is no longer controlling the channels as the original truth table) while the input voltage of A,B,C pin is correct. (The output of the Hex inverter is correct, and by theory the 2 HMC183 SHOULD be synchronized) The problem remains after changing the CD74HCT04PWR and all other components.

In addition to this situation, sometimes one or multiple channels would simply lose all reflections and S21 responses.

When HMC183 is replaced with new ICs, the system works fine, however sometimes the HMC 183 fail again. I have not able to identify the actual causes by now.

The system schematic and the system truth table is attached, The TTL input is lowered by a clamping circuit (from +5v~0v to 0v~-5V). the Hex inverter is powered by -5V through GND pin  to work with 0~-5v TTL signals. All DC power supplies are made by voltage-stabilized DC power source. All instruments and the filter bank are grounded. 

So the Questions are:

1, in what circumstance would some of the channels fail while others works fine in HMC183?

2, In what circumstance would the HMC183's Pin A,B,C fail to control the right channel?

3, are there any problem with the DC and TTL input circuits in my system?

4, what are the absolute maximum input voltage and current for Pin A,B,C of HMC183? Would low voltage cause this kind of problem?

I'm stuck with this problem for days, and lost 8 HMC183 chips for this problem. Help needed urgently, Thanks in advance!!



It seems like your driver circuit is not generating correct bias for the low state and high state of the driven HMC183QS24. I suggest you to depopulate HMC183QS24 parts and check high and low voltage levels on A,B,C control inputs if they are within range specified for the HMC183QS24.

The zener diode (BZT52H-B5V1) you use is rated at high zener current of 5mA which could be why the correct high and low voltage levels are not produced. I suggest you to replace your zener diodes with the SM16Z4689 Zener Diode Array which is suitable for that kind of driver circuit.



  • Thanks a lot, like.

    I have requested samples of SM16Z4689 and will try your recommendation.

    Currently, with BZT52H-B5v1, when the control board is supplied with +5v input for D0 D1 D2 pin, measured control output (HMC183 input) is totally correct and meets the truth table, (either exact 0V or -4.99V)

    When the control board input is below +1.5V, the control board output remains 0v. When the control input is above 2.1V, the control board can successfully identify the high state of input signal. However, when the control board input is between +1.5V~+2.1V, the control board output will not be stable, it shows -3v something. and the on/off state of D0, D1, will effect voltage output of C pin, which is not suppose to happen (because C pin is only connected to D2).

    Seems like when the control input is between +1.5V~+2.1V, the out put of the HEX inverter is disordered. Will it be a potential cause for the damage of the HMC183?

    So do you have any further suggestions for this? thanks a lot

  • Hi,

    If the digital control inputs are kept an indeterminate voltage level for a long period of time, the part could be damaged due to the large leakage currents flow on internal circuitries. All the digital control inputs of HMC183QS24 should always be kept within the valid logic levels (VIHor VIL) specified in product datasheet.


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