codewiz
Joined: 14 Sep 2008
Posts: 75
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 28 Jun 2009 9:29 difference between 74hc and 74ls |
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| please, i like to know about d difference between LS and HC versions of 74xx series in terms of power supply range, output current ability i.e the source current, robustness. i really need an expert analysis. can i replace say74HC164 with 74LS164? What are the consequences?
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Thanhlongbin
Joined: 13 Jul 2009
Posts: 48
Location: Hanoi-Vietnam
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13 Jul 2009 11:35 difference between 74ls and 74hc |
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| codewiz wrote: |
| please, i like to know about d difference between LS and HC versions of 74xx series in terms of power supply range, output current ability i.e the source current, robustness. i really need an expert analysis. can i replace say74HC164 with 74LS164? What are the consequences? |
There're many diff. Some major are here:
1. Supply voltage: 74LS': 5V+/-0.2. 74HC': 2V to 6V
2. Output current: 74LS' is asymmetrial I-High~ -0.4mA, I-Low ~ +4mA; 74HC'is symmetrial Ih,Il =4mA
3. Output voltage: 74HC's has better wave form (U-low=0v, U-high=4V)=> good for output to DAC !!!.
3. Propogadation delay: 74LS' ~ 3ns, 74HC' ~ 6ns.
4. Fan-out capacility: both are the same.(10-16 max.)
In my experience, for low rate application (under 10MHz clock), LS and HC can be exchanged each by other. For higher rate clock (20MHz), I use 74HC' with 3v3 voltage supply!!!!
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