Hi,
If OPA as TLV379 is not powerd up, and we apply a voltage which has a 1.2V maximum to IN+ and IN-. Then what effect to OPA may produce? Can it influence the parameters of OPA? If we design as it, what attention should we pay to? Please give us some suggestions, thanks!
Hello Shawn,
Obviously, the op-amp will not be functional with no supply voltage - so NO specifications are applicable when Vs = 0V.
The inputs are protected by ESD diodes from each input to both supplies.
Below diagram shows the placement of the ESD diodes.
Like "normal" diodes, they will start conducting about 400mV, and will be in full conduction by 800mV.
If VCC is at 0V, and a positive voltage is applied to an input, then the upper ESD diodes will forward bias and clamp the input to the V+ line. Essentially - you will be back-feeding the supply line through the ESD diode.
Current through the diodes needs to be limited - as they are not designed for continuous power dissipation. Current must be limited to below the Abs Max value of 10mA. The less the better.
Series resistance can be added in series with the input to limit the current. Adding a minimum of 1kohm (or more) per volt is required.So at a minimum you should have 2K of series resistance - though more is better - for a 2V input. This resistance can be part of any restive dividers, feedback or filters.
See the TI Precision labs series on ESD and Electrical Over-stress (EOS) for more information:
