How do you determine pull up value?
The actual value of the pull-up’s resistance depends on the impedance of the input pin, which is closely related to the pin’s leakage current. A rule of thumb is to use a resistor that is at least 10 times smaller than the value of the input pin impedance.
What is the purpose of a pull-up resistor?
In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC.
Why do I need external resistors for 3.3V?
Requires an external load resistors on the 3.3V supply, if the 3.3V system has a very low minimum current consumption. Possible noise on the 3.3V supply due to current injected into it. The 3.3V input must have a high impedance (small input leakage, such as CMOS). SERIES RESISTOR WITH EXTERNAL SCHOTTKY DIODE CLAMP TOWARD THE 3.3V LINE.
What is the voltage drop from 5V to 3.3V?
The input of the 3.3V system is pulled up to 3.3V through R1. Then the 5V-system outputs 0V, the diode is forward biased, so the voltage at the 3.3V input will be the forward voltage drop of the diode: about 0.6-0.7V for silicon diodes, or 0.35V for Schottky diodes.
Can a pull up resistor increase high level voltage?
This solution is most often rejected due to insufficient margins. If the above conditions are close, you can often boost the high-level output voltage slightly with a pull-up resistor (to 3.3V) and direct connect the signals. The pull-up resistor can provide a small amount of high-level voltage increase.
Can a 5V input be connected to a 3.3V output?
Direct connection between a 3.3V CMOS and a 5V TTL device is possible. First, when interfacing with TTL inputs, any “modern” CMOS output will work, as the high level output voltage of a 3.3V CMOS is close to 3.3V (note!