I'm trying to design a circuit with MAX8934AETI+. I'm confused about how to connect a pin to logic level high. For example, pin 6 in the picture below is meant to be connected to logic level high to assign the input current limit to 500mA, but does this mean I need to put a resistor in series with it? I do not see anything else in the datasheet about this.

Typical Application


2 Answers 2


On your datasheet, the table on page 7 gives the logic thresholds as low max of 0.4 V, high min of 1.3 V. The absolute max ratings allow 0 to 6 V on PEN2. This means it can be connected directly to a VCC of 5 V.

However, resistors are cheap, expose a test point, and allow you ground that point during debug or test if that's a useful thing to do, or easily hand modify a PCB to change the function. If you've got space and the budget for a resistor, then it doesn't hurt to use one. Use one on every pullup and pull down if you can, you never know when the ability to easily change a 'fixed' pin is going to save you some trouble.

You might wonder why I looked at the absolute max ratings. The idea of pulling inputs up with a resistor being a very good idea dates back to the days of TTL, when the VCC absolute max was 7 V, but the inputs could only tolerate 5.5 V. If the rail spiked to between 5.5 V and 7 V during some fault condition, then ICs with a resistor pullup would survive, those with direct pullups might not.


For ATE testability, resistors are used, but not necessary for CMOS, otherwise.

However for TTL due to failure modes with reverse Vbe inputs >5.5 V a current limiting 10k resistor can be shared by 10 inputs.

These design rules were set about 50 yrs ago.


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