Other Parts Discussed in Thread: SN74LS07, SN74HC244
[ SN74LS244 ] Start-Up Behavior
Hi,
My customer tests the SN74LS244 together with photo couple as drawing below.
During their initial evaluation, they have seen unexpected pulse from photo coupler output.
I assume that this is expected behavior of the combination of SN74LS244 and photo coupler. During voltage ramp-up, from certain voltage, SN74LS244 starts its operation and try to make output low during the input signal is in low level(<0.8V). Thus we have voltage difference which enough to turn on photo coupler.
To prevent this behavior, what we need to do is replace SN74LS244(3-state output) to some other device with Open-Collector or Open-drain output.
Do you have any other ideas with SN74LS244?
The reason why this behavior is unexpected for my customer is because they have used SN74LS07 which is open collector output.
With this device, output voltage of SN74LS07 just follows VCC5V, so there is no voltage difference.
It's appreciated if you can share your idea with me.
Regards,
Ken
