opa827 reverse battery protection

Matt,

You may NOT reverse supplies in any op amp since doing so would forward-bias ESD protection diodes - see below.

Needless to say no op amp can work with its supplies reversed and doing so without limiting the current to 10mA or less will permanently damage the part.

hi marek,

thanks for the diagram. unfortunately i did recently have a big oops and installed a single-to-dual dip8 adapter backwards in its socket. the 100ma fuse on the mains input blew more or less instantly. however the device still appears to function properly.

so a large current would flow across the normally reverse biased diodes. pardon my limited understanding here, but would the pair of diodes function similar to a simple voltage divider with regard to the voltage at the inputs and output of the op amp?

in other words, if the resistance of each of the two diodes in the pair were approximately equal when forward biased, and the supply rails were closely matched at +12/-12V, then the voltage at the inputs and outputs would be 0v, correct? i'm trying to figure out if the device normally connected to the inputs of the op amps was exposed to harmful voltage/currents. there are 2.4k resistors between the device and op amp.

thanks,

-matt

Matt,

If you truly had 2.4k resistance in series with supplies, this would limit the current thru forward-biased ESD diode to less than 10mA (24V/2.4k).  However, you mentioned 100mA fuse being blown up which makes me think 2.4k resistance is not in series with supplies and therefore you need to analyze in detail the current path - was 100mA current flowing thru the device or thru an external path? 

If 100mA current did flow thru OPA827 even for a short instant of time, it may have partially damaged internal circuitry of the op amp; thus OPA827 may seem to continue to operate after exposure to 24V reversed supplies but some transistors may have been compromised - it typically takes just 3V of reverse-biased Base to Emitter junction to damage any of the internal transistors.  Under such scenario, the op amp may not meet PDS specifications and/or its operating life may have been drastically shortened.

hi marek, the 2.4k was between inputs of the two opa827 and the output of my ak4396 dac chip. very low impedance to the power rails. i've ordered a replacement pair of opa827. should i be concerned about possible damage to the dac chip as well? the output of the opa827 and ak4396 were connected, even if isolated by 2.4kohm :( would the opa827 output the v+/v- rail voltages on its input or output with the polarities reversed? thanks, -matt

Matt,

2.4k between the output of AK4396 DAC and OPA827 input should limit the current to less than 10mA so as long as the DAC output includes the ESD diodes to its rails (based on 0.3V voltage spec limits I think that it does - see below) reversing supplies on OPA827 should not have damaged DAC.