I am planning to use Adum3210 isolators between 2 PIC (5Volts, 20-30khz Data Transmission) Should I use serial current limiting resistors before and after ADUM3210? OR should I use no resistor?
icoupler digital isolator has a CMOS level input characteristic, the impedance is pretty high, so the input current would be limited to like uA level.
for the output we have a totem-pole structure, the output imdedance is rougly 60ohm. the load current would cause a voltage drop inside the chip and the resister in the signal path, and finally impact the voltage on the input port of PIC. we need the impedance and input logic voltage threshold of PIC to determine if we need to insert current limit resistor.
Hope this is helpful.
So if I need 10ma at output of Adum3210 should add 440 ohm extra resistor to output?
I will use at 5 Volts (60+440ohm).
I didn't understand very well from table. fox
this will only happen if you have 0ohm input impedance on PIC. the output current does not only depend on the current limit resistor but also the input impedance of the device which receive this signal. Take adum3210 for example, its input impedance is hundreds of kohm. so even if no current limit resistor, the load current could only be like several uA.
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