OPA277: There have the glitch when the OPA277 was operated below 2V, What is the cause and How can I solve or avoid this problem?

Hi,

is the OPA277 outputting a voltage during power down which is higher than its supply voltage? In this case the voltage glitch could be delivered by the cap in the feedback loop of OPAmp.

Can you please post a complete schematic and explain in detail whan can be seen in the scope plot?

That a normal OPAmp outputs a glitch when powering down is fully normal, because at some point the internal biasing circuitry (constant current sources, aso) stops working and the output voltage is no longer in regulation.

Kai

Hao,

The minimum operating supply voltage for OPA277 is +/-2V  - see below.  Below +/-2V supply voltage the internal circuitry cannot bias up properly resulting in the op amp operating in the open-loop fashion - this results in the output collapsing against one of the rails - a very normal condition in all op amps.

The RC in the feedback of the buffer is for low-pass signal filtering, with cut-off frequency of fc=1/(2Pi*R*C).

Hi Hao,

your last scope plot shows that the output voltage glitch is within the supply voltages. Or by other words, the glitch is not exceeding the supply voltages of OPAmp. So this is fully normal.

If the glitch is unwanted, you can remove it by adding a switch to the output of OPAmp which always opens when the supply voltage falls under a certain level. At the output of switch you will need a pull-down resistor to signal ground.

Another option is to clamp the output voltage of OPAmp to signal ground by the help of a swicth whenever the supply voltage falls under a certain level. Then a resistor in series to the output of OPAmp will limit the current through the clamping switch. Provided the signal voltage isn't too high, even a simple NPN transistor could be used for the clamping switch. This method can often be seen in CD players and other audio circuits.

Kai