How do you calculate pull-up resistors?
Calculate actual values of pull up and pull-down resistor In order to calculate pull-up and pull-down resistance, we need to first apply the formula in Ohm’s Law: Resistance = Voltage/Current, or R= V/I.
How large should a pull-down resistor be?
You generally want a large resistor value (10kΩ), but you don’t want it too large as to conflict with condition 2. A 4MΩ resistor might work as a pull-up, but its resistance is so large (or weak) that it may not do its job 100% of the time.
Why a pull-up resistor is required for an open collector gate?
A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. Some open-collector gates, such as the 74LS06 are capable of driving larger loads because their outputs can be connected to supplies of up to 30 volts via an external pull-up resistor.
How do I choose i2c pullup resistor?
Notice the two pull-up resistors on the two communication lines. Resistor selection varies with devices on the bus, but a good rule of thumb is to start with 4.7kΩ resistor and adjust down if necessary. I2C is a fairly robust protocol, and can be used with short runs of wire (2-3m).
Why use 10k pull-up resistor?
The 10k resistor (R2) is there the make sure the voltage on the pin is held at a stable high level. “High” as in a value close to the supply voltage. The reason that I chose the value 10k is that from my experience I know that 10k to 100k pull-up resistors usually work fine in almost all circuits.
What is an open drain output?
An open-drain or open-collector output pin is driven by a single transistor, which pulls the pin to only one voltage (generally, to ground). When the output device is off, the pin is left floating (open, or hi-z).
What is a weak pull-up resistor?
A resistor with relatively high resistance is called a “weak” pull-up or pull-down; when the circuit is open, it will pull the output high or low more slowly, but will draw less current.
How does a pull-down resistor work?
The pull-down resistor holds the logic signal near to zero volts (0V) when no other active device is connected. It pulls the input voltage down to the ground to prevent an undefined state at the input. It should have a larger resistance than the impedance of the logic circuit.
What is 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. A pull-up resistor effectively establishes an additional loop over the critical components, ensuring that the voltage is well-defined even when the switch is open.
What is open collector pull-up resistor?
Open collector outputs require a pull-up resistor (R in the image above) for the output to be able to properly “output high”. The pull-up resistor is connected between the output pin and the output voltage (Vcc in the image above) that is desired for a high state.
How many pull up resistors for I2C?
The I2C bus must have pull-up resistors, one on the SDA line and one on the SCL line. They’re typically 4.7K or 10K ohm, but should be in the range of 2K to 10K.
How many pull ups I2C?
The I2C specification allows a maximum of 3 mA pull-up current on each I2C line.
Can a pull up resistor be used with an open drain?
There are few things that have to be considered when using a pull-up resistor with the open drain output configuration: Rising edge slope – The pull-up resistor in combination with the inherent capacitance of the line forms a low-pass filter.
How big of a pull down resistor do I Need?
All these parameters are mentioned in the datasheet. We can use maximum of 500 ohm resistor for Pull-down. But again, we should use a resistor value less than 500 ohms. We can say a pin is “open collector output” when the IC can’t drive the output “HIGH” but can only drive its output “LOW”.
How does a pull up resistor work in an IC?
Since the output is either ground or open circuit, we need to connect an external Pull-Up resistor which can turn the pin “HIGH” when the transistor is OFF. This is same for Open drain; the only difference is that the internal transistor inside the IC is a MOSFET.
How does a pull up resistor work in a logic gate?
With a pull-up resistor connected, the output still works in the same way as a normal logic gate in that when the output transistor is OFF (open), the output is HIGH, and when the transistor is ON (closed), the output is LOW. Thus the transistor turns ON to pull the output to a LOW level.