[sdiy] NJM2068 gone bad

Michael E Caloroso mec.forumreader at gmail.com
Fri Jun 26 15:46:19 CEST 2020


Diode protection only works if they are connected to a voltage
potential. Either under power, or if the PSU is turned off resulting
in near zero voltage potential.  If the IC or circuit board is not
connected to a voltage potential then the components are vulnerable to
ESD damage.  When handling them under this condition you must still
use ESD safe handling precautions.  You can't expect end users
assembling the module in a system to follow ESD safe procedures.

MC

On 6/25/20, Tristan <tu at alphalink.com.au> wrote:
>
> Is the device completely enclosed or can the circuit board and/or components
> be directly
> touched during handling? Do your testers follow ESD safe procedures? ESD
> protection on the
> inputs will not protect devices on the board if they come into direct
> contact with a statically
> charged body. Even the internal protection diodes on the chip have limits
> and will break down
> with repeated exposure to shocks.
>
> /Tristan
>
> On Fri, Jun 26th, 2020 at 5:45 AM, "Frédéric (Opensource)"
> <marzacdev at gmail.com>
> wrote:
>
>> Hi Tom, hi Jay,
>>
>> first, thank you for your answers.
>>
>> For the ESD protection I meant TVS diodes, not regular
>> bipolar diodes so the protection is for both pulse polarity.
>>
>> For current injection, there is a 20k input impedance that
>> limits the risk in case of overvoltage below the threshold
>> of the TVS (which is about 16V, this parameter has a big
>> tolerance).
>>
>>  > was the system and/or part known good when it shipped
>>  > out?
>>
>> Yes, it seems to have correctly passed the factory test bench.
>> The system was used by a tester who did not noticed any weird
>> behavior and then shipped over to an other tester who noticed
>> the distortion immediately.
>>
>> Today, I made a series of tests going above all ratings on power
>> rails input levels and everything I could think of and could not
>> reproduce the issue, damaging the circuit. Also the device has
>> successfully passed all ESD tests when we went for the CE / FCC
>> compliance.
>>
>> So maybe a problem of soldering or a defective chip.
>>
>> Thanks again for your time and answers,
>> Frédéric
>>
>>
>> Le 25/06/2020 à 00:23, Tom Corbitt a écrit :
>> > Just to clarify, was the system and/or part known good when it shipped
>> >
>> > out?
>> >
>> > Assuming it was, you mention the protection ESD diode and reverse
>> > protection but I wonder does the circuit have any other protection for
>> >
>> > voltages below ESD levels but over the safe maximum for the chip?
>> >
>> >  I see +/- 18V max listed on the datasheet I looked at.
>> >
>> > That's just my first instinct, that someone plugged in something with
>> > too great of a potential and it damaged one of the two channels.
>> >
>> > It's easy enough to test and there are very simple fixes if it is an
>> > issue (36V zener with a current limiting resistor in parallel with
>> > input is a very basic old school way to do it, plenty of smarter
>> > folks here on the list with better ideas and ways I'm sure)
>> >
>> > Tom
>> >
>> >
>> > On Wed, Jun 24, 2020 at 1:23 PM Frédéric (Opensource)
>> > <marzacdev at gmail.com <mailto:marzacdev at gmail.com>> wrote:
>> >
>> >     Hi to everyone,
>> >
>> >     In a client audio design, I used a NJM2068 dual op-amp
>> >     as the input signal conditioner before the ADC circuit.
>> >
>> >     The op-amp is powered with symmetrical supply rails (+12V, -12V)
>> >     provided by the power bus of an eurorack system.
>> >     Rails are protected by series shottky diodes therefore the
>> >     case of a polarity reversal can be discarded I presume.
>> >
>> >     Audio input has an ESD protection diode and the impedance
>> >     between the + input of the amp and the input jack tip is about
>> >     20k (resistor). The input is specified for "eurorack level"
>> > signals.
>> >
>> >     Unfortunately, after the field tests, we got back one module
>> >     whose input op-amp had a defective channel. Input signal would
>> >     be saturated while being far away from the rails.
>> >
>> >     Had any of you a bad experience with this component?
>> >
>> >     I am also open for all suggestions about what wrong could
>> >     have happened?
>> >
>> >     Best from Bonn,
>> >     Frédéric
>> >
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>> >
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