I am using MCP16312-E/MS buck regulator and need the component to always be on. I am therefore connecting the enable pin to the Vin supply. Do you need a current limiting resistor? Whilst the resistor I have in series with the enable pin will limit the current, it will also 'take' all of the supply voltage so the voltage at the enable pin itself will be 0V? Is this correct? If so, what should be done instead?
I absolutely agree with @DirkBruere - you should read the datasheet.
I read the datasheet and it says nothing
Let's see if that is true.
First, the very first picture in it has EN pin connected to Vin. This tells you that for "always ON" applications you don't need the resistor at all.
Second, in the Absolute Maximum Ratings you can see that maximum input voltage is 32V and EN pin can be 0.3V higher, i.e. 32.3V maximum. This confirms that you can connect EN pin directly to input voltage.
Third, in DC Characteristics you can see that maximum EN Input Leakage Current is 1 microampere at 5V. It won't be too much higher than that at higher input voltages.
1 uA current through 1 MOhm resistor allows you to calculate voltage drop on resistor. In this case 1uA * 1MOhm = 1V. So, if your input voltage is 5V then the voltage on EN pin would be 5V - 1V = 4V.
Finally, in the same table you look for EN input voltage characteristics, and find that EN Input Logic High minimum is 1.85V, so anything above it will switch device ON. Calculated above 4V voltage is certainly sufficient. However depending on input capacitance the start-up time can be quite high. For this reason 1k-10k resistors are more typical for this pin, just as @DirkBruere suggested.
So, from the datasheet it is clear that 1) you don't need resistor at all, but 2) if you add it then 1 MOhm resistor will work, although smaller value is more appropriate.
No, everything in the datasheet says there is no need for a resistor, EN can be directly connected to Vin.
Datasheet says EN pin has no internal pull up or pull down resistor, it must not be left floating, and it can handle whatever voltage there is on Vin.
However, it is not wrong to connect it via a resistor, for some purposes it might be even beneficial to do so.