Electronic – TTL, Totem Pole vs. Open Collector Output

digital-logiclogic-leveltransistorsttl

What is the difference of these two ttl nand gates?

What is a totem pole, what does it do and what is it used for?

When connecting multiple ttl logic gates together is it better to use one or the other?

open collector

totem pole

Best Answer

Totem Pole output drives the output high and low. Open collector will only pull the output low; it does not drive the output high, only releases the output to float.

Multiple open collector outputs may be tied together to operate in a wire-OR arrangement, where any output may pull the output low. In this case, a pullup resistor is used to establish a logic 1 when all outputs are off.

Open collector may also be used to drive non-gate loads, such as LEDs, small solenoids, etc., as long as the load voltage and current is within the rating of the open collector device.