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opa171 failing in field

Brent Bouws
Prodigy 10 points
Other Parts Discussed in Thread: OPA171

Hello,

  We are using the OPA171 in the production design of a LED luminiare control module.  The OPA is acting as a buffer/follower in a 0 - 10 VDC output dimming control circuit.  The circuit is fed by a PWM from a microcontroller.  The Vcc voltage is 24 VDC.  The 24 V is generated by a AC / DC converter that converter line voltage to 24 VDC.

  We are having some of our units returned, where this opamp has failed.  The failure mode is that the impedance from Vcc to Gnd is 30 - 80 ohms.

  Has anyone observed this failure mode before on the OPA171 or similar component?

  What scenarios could cause this failure mode?

  I have not been able to repeat the failure mode in the lab.  I tried increasing the Vcc with a bench supply up to 50 V, but that did not induce the failure mode.

I had one unit exhibit this failure mode while it was in our office space.  Thus, I know that it was not being exposed to extreme temperatures.  Attached is a snippet of the schematic where the opa171 is used.

Any help is greatly appreciated,

Brent

  • 0
    TI__Guru 63790 points

    Brent,

    You have to be very careful how you measure the impedance between the positive and negative supply pins so you do not forward bias p-n junction where negative supply (p-type material) is above the positive supply (n-type material).  In other words, reversing the voltage on power supplies (for example, by using an ohmmeter with wrong polarity) would forward bias parasitic p-n junction and result in erroneous reading.  To this end, you should measure known good units of OPA171 to make sure that your diagnosis of low impedance between power supplies pins are true indications of the damage to the IC. 

    Any actual 30-80 ohm resistance from positive to negative supply would point to the electrical overstress, EOS, damage that most likely occurred due to excessive transient voltage between the supply pins; e.g. high voltage spikes coming from AC/DC converter during power up sequence.  Any voltage in excess of the maximum rated supply voltage of 40V (see Absolute Maximum Ratings table below) could cause such damage. 

    In order to prevent such damage, Zener diodes or transient voltage suppressors, TVS, with the maximum 40V breakdown voltage, should be placed on each of OPA171 supply pins – below please see the complete EOS protection scheme.  Also, please watch the Precision Labs four-part video series on the subject of electrical overstress.  It covers a lot of details of selecting the TVS diodes and series limiting resistors to prevent EOS damage.  Below is a link to the TI Precision Labs: