# Do I need to connect a resistor to either one of the 2 input pins of this “and” logic component? If so, what would be the value for it?

The said component is sn74lvc1g08 from TI, datasheet.

I was planning on connecting 3 1.5 volt AA batteries (in other words, 4.7 or 4.8 volts max in total) to one of the input pins (either A or B) and I'm quite sure although not 100% sure that a resistor is necessary, but I don't really know how to calculate the value of the resistor.

Please give a rather detailed procedure regarding the method of calculation. Thanks in advance.

I'm working on some safe-critical project and I'm ticking in "extremely meticulous" mode so please bear with me.

• an AA battery at 0.5V is quite dead already, 3 batteries would probably never trigger a "low" input (or at least not reliably) – Wesley Lee Apr 12 '16 at 9:05
• Could you give a bit more context - why are you connecting the batteries direct to an input pin? Are they the same batteries that power the circuit? – pjc50 Apr 12 '16 at 13:58
• I failed to find the button to reply to each one of you so I'll make my response in one go: – user6107491 Apr 13 '16 at 1:16
• I failed to find the button to reply to each one of you so I'll make my response in one go: I do not anticipate it to ever give a "low", I have other mechanisms to measure the battery level, this circuit in discussion is used to decide whether a battery was plucked out of its chamber, so there's the context. And no, it is not the batteries which power this particular circuit, it powers a "main circuit" other than this one, this one is used to monitor the 3 batteries and has its very own battery as an independent power source. – user6107491 Apr 13 '16 at 1:23

• @user6107491 You are correct, the input of a CMOS transistor looks like a 10$^{12}$Ω resistor shunted by a 5 pF capacitor. So the input current is less than 1 µA. Any additional resistor in front of the input would have no effect. – tcrosley Apr 13 '16 at 2:29