Hi
Can I ask a simple question?
There is no Absolute Maximum Ratings of VREF. I don't know this is usually but I would like to know how much is the Absolute Maximum Ratings of VREF.
Can we assume it same as cathode voltage?
Best Regard,
Koji Hamamoto
Hi Koji,
The REF input is a current input pin and not a voltage input pin. This is the reason all '431 devices such as LMV431 or TL431 only specify the current into the pin. We always recommend a series resistor with the VREF pin such as the images below. In both of the images below the series resistor is between the input for comparison and the REF pin which helps limit the current into the pin. It is not recommended to apply a direct voltage to pin unless that voltage has a maximum voltage around 1.24V for LMV431. I would not use cathode ABS max as VREF ABS max. If you need us to review a schematic, we can.
For example in the first image above, I have the data below showing the effect of raising the voltage on the REF pin on TL431. I also show how the IREF increases because the VREF stays constant for the same setup. I would design the resistance to keep the IREF lower than 1/10 of max current at worst case conditions. While this is for the TL431, the behavior is similar to the LMV431.
-Marcoo
