Input resistance problem

chenbingjy

Input resistance problem [Copy link]

The picture above is a manual of a stepper motor driver. What does the input resistance of 220 ohms mean? Does it mean that an external 220 ohm resistor is required? Thank you!

maychang

"Does it mean that an external 220 ohm resistor is required?" No. The input resistance of 220 ohms means that the input terminal to the ground is equivalent to a 220 ohm resistor, which can be regarded as a 220 ohm resistor connected between the pin and the ground inside the chip or module. This puts forward certain requirements for the drive signal: when the input high level is 4V, the drive circuit must be able to supply at least 4/220=0.018 (A) current.

chenbingjy

maychang posted on 2018-8-20 16:17 "Does it mean that an external 220 ohm resistor is required?" No. The input resistance of 220 ohms means that the input terminal to ground is equivalent to a 220 ohm resistor, ...

Thank you

chenbingjy

The manual says that PU+ can be connected to 24V or 5V. If it is higher than 5V, a current limiting resistor is required. If it is connected to 24V, is the current limiting resistor value calculated like this? 24-5=19 19/0.018=500 ohms. At least 500 ohms

maychang

chenbingjy posted on 2018-8-20 16:36 The manual says that PU+ can be connected to 24V or 5V. If it is higher than 5V, a current limiting resistor needs to be connected. If it is connected to 24V, is the current limiting resistor value calculated like this? ...

The manual does not say what the input resistance of the PU+ end is. For things like this, it is best to contact the customer service of the module manufacturer.

chunyang

It is estimated that there is an optocoupler LED end inside, and there is a current limiting resistor for 5V. You can check the input current index and use Ohm's law to calculate. If PU+- and DR+- are connected to the LED side of the optocoupler, and 220 ohms is the current limiting resistor, then the calculation is very simple, but be sure to confirm it. If the manual cannot confirm it, contact the manufacturer.