What is the disadvantage of having a pullup resistor with a low resistance?
Pull-up resistors may be used at logic outputs where the logic device cannot source current such as open-collector TTL logic devices. Some disadvantages of pull-up resistors are the extra power consumed when current is drawn through the resistor and the reduced speed of a pull-up compared to an active current source.
How do you find the pull up and pull-down resistor value?
First, use IEN, ILKG, and Equation 1 to find the current through the pull-up resistor, IPull-up. Now that IPull-up has been calculated, the maximum value for RPull-up is found by using Equation 2. An output voltage, Vout, of 1.8 V is used as an example. The next step is to find the minimum pull-up resistor value.
What happens when the pull up resistor is too low?
If the resistance value is too low, a high current will flow through the pull-up resistor, heating the device and using up an unnecessary amount of power when the switch is closed. This condition is called a strong pull-up and is avoided when low power consumption is a requirement.
How does a pull down resistor work on a microcontroller?
A pushbutton switch is connected between the supply voltage and a microcontroller pin. In such a circuit, when the switch is closed, the micro-controller input is at a logical high value, but when the switch is open, the pull-down resistor pulls the input voltage down to ground (logical zero value), preventing an undefined state at the input.
How is a pull up resistor connected to a Vcc supply?
This condition means that their output is either grounded when LOW, or floating when HIGH, so an external pull-up resistor, (Rp) needs to be connected from the open-collector terminal of the pull-down transistor to the Vcc supply.
How are pull up resistors used in a logic circuit?
Pull-up resistors are resistors used in logic circuits to ensure a well-defined logical level at a pin under all conditions. As a reminder, digital logic circuits have three logic states: high, low and floating (or high impedance).