Dear Specialists,
My customer is considering LMV824 and has a inqury.
Could you please advise?
How is the output when input is out of Input Commom-Mode Voltage Range?
The condition is Voltage follower.
For example, Vcc=5V,Vin=4.5V
(VCM is from -0.3V to 4.3V, therefore 4.5V is out of spec.)
How is the output?
(1) unstable
(2) normal output (4.5V)
(3) causes satulation
(4) other result
Best regards,
Shinichi
Hi Sinichi,
The output could saturate to either rail, or "float" at the common mode limit point.
There are many factors that contribute to the results: Temperature, supply voltage, native offset, differential voltage, current into input pin and the actual circuit configuration. Every device family has a different behavior.
When you violate the input common mode, you cut off the input stage causing it to turn-off. When the input stage dies, all control is lost of the output. Which way the output falls then depends on internal leakages. Once the input stage is cut-off (say, at 4.6V for a 5V supply), going higher makes little difference - as the input stage is already cut-off.
Going over V+ will cause the upper ESD structure to start to conduct, clamping the input to V+.
At Vcm > (V+) + 0.5V, the input currents start to become significant (mA's) as the diodes conduct. Series resistance is needed to prevent large currents and/or external clamp diodes should be used.
Regards,
