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MPY634: MPY634 V+ pin and Input pin internal short problem

hoonmin Jang
Prodigy 60 points
Part Number: MPY634

Hello 

I'm using MPY634 mixer chip

As shown in the picture below, the power pins(15V/-15V) are connected to the power supply and only the ground is connected to the x2 y2 pins,

but an internal short has occurred between the input terminal and the V+ power pin.

In what cases can an internal short between the input pin and the power pin occur? please tell me about that case.

And could the cause be caused by the soldering iron touching the pin for a long time?

Thank you.
  • 0
    Guru 140200 points

    Hi Hoonmin,

    I would try to clean the adapter board. Take a toothbrush and lots of spirit. Then blow the spirit under the chip away with your mouth and dry the board thoroughly before powering again.

    Kai

  • 0
    TI__Genius 9115 points

    Hi Hoonmin,

    There appears to be a very large amount of solder flux residue on your breakout board. Solder flux is a conductive material and flux residues left on the board can become conductive bridges that will cause electrical shorts between pins.

    I recommend using a flux remover solvent for PCBs and a toothbrush as Kai recommended to thoroughly clean your board.

    It is possible for an inexperienced PCB assembler to damage component packages, pins or PCB traces with the solder tip, in which case you must start over with a fresh board and components. Typically that type of error would be visibly obvious, such as a component pin falling off of the package or the PCB trace delaminating from the board.

    It is always recommended to clean a PCB after it is assembled or modified with solder flow.

    Regards,

    Zach

  • 0 in reply to Zach Olson
    Prodigy 60 points

    Thank you.

    As you answered, I cleaned the solder flux and tested again, but the internal short is still there.

    And when I checked on a total of 4 chips, there was a short between the output and -Vs pins in common.

    Since internal short has already occurred due to solder flux, does internal short still occur even after wiping it off? 

    And maybe it has something to do with the EOS issue?
  • 0 in reply to hoonmin Jang
    Guru 140200 points

    Hi Hoonmin,

    be very careful when you make measurements with an Ohm-meter or else trying to find out an assumed short-circuit between certain pins of chip. This can easily destroy the chip by violating the absolute maximum ratings. See the datasheet. Also, the input voltages must never exceed the supply voltages. So, during a power-up, first power up the MPY634, then apply the input signals. And vice versa when powering-down, first remove the input signals, then power down the MPY634.

    Kai

  • 0 in reply to hoonmin Jang
    TI__Genius 9115 points

    Hi Hoonmin,

    Upon visual inspection of your board do you see any remaining solder or flux residue bridges across the amplifier pins or PCB copper? I notice in your image there is at least one PCB trace that has exposed copper due to solder mask removal from your soldering iron. These types of errors in PCB soldering produce additional surface level conduction paths that can result in electrical shorts.

    If the device was powered on while the circuit was shorted it is possible that the device was damaged due to violation of the absolute maximum ratings.

    Additionally, as Kai mentioned, an ohm-meter functions by applying a voltage to a circuit and measuring the resulting current. If the amplifier is powered off (Vs = 0V) and your ohmmeter applies a voltage to the input pin of 4V for example, the absolute maximum ratings have been violated and your device can be damaged.

    The following TI Precision Labs video provides an introduction to electrical overstress and how an amplifier can be damaged.

    https://training.ti.com/ti-precision-labs-op-amps-electrical-overstress-introduction?context=1139747-1139745-14685-1138807-13956

    Regards,

    Zach