How to Handle Open Collector Output pins

Open Collector Output pins should be tied to a valid logic level so the output remains fixed at a valid voltage level when the device turns off. Wire AND-ing requires a resistor pull-up which needs to function for the range of devices tied to the wire-AND. The minimum value of pull-up is calculated while only one output is low, the maximum value of pull-up is calculated while all outputs are high. Both equations are listed below:

R_{Pull-Up {min}} = ( [V_{cc {max}} - V_OL] / [I_OL - Num_{Input Unit Loads {Low}} * I_IL] )

R_{Pull-Up {max}} = ( [V_{cc {min}} - V_OH] / [I_OH * Num_{Output Unit Loads} + Num_{Input Unit
Loads {High}} * I_IH] )

Num_{Input Unit Loads {Low}} = the number of input devices connected to the wired-OR
Num_{Output Unit Loads} = the number of Open Collector devices connected together

IC devices use Open Collector outputs for a number of reasons:
... Wiring AND-ing two or more Open Collector device outputs together
... Allowing the device to drive another type of device at a different V_cc.

How to Handle Tri-State Output pins
How to Handle Unused Input pins
How to Handle Bus-Hold Input Pins

**Related pages on this site:**
. Standard Logic Voltage Thresholds .	. Bus Logic Thresholds .	. Logic Speed x Power Chart .	. Trace Termination .	. Ground/Power Planes .

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