# fan out of 74ALSO4

Discussion in 'General Electronics Chat' started by muni, Sep 2, 2008.

1. ### muni Thread Starter Active Member

Jul 29, 2008
45
0
QUESTION FROM GATE PAPER AGAIN. REQUEST ANSWER

the inverter 74 ALSO4 has the following specifications.
IOh max = -0.4 mAmp,
IOL max = 8 mAmp
IiH max = 20 mAmp
IiL max = -0.1 mAmp

Calculate fan out based on the above will be
a) 10 b) 20 c) 60 d) 100

i request how to calculate the fan out, though book gives answer but my request is how to calculate this.

SIR I ALSO REQUEST HOW TO UPLOAD MY FILE THAT IS AVAILABLE IN MY PC. I TRIED THROUGH ATTACHMENT I COULDN'T DO IT. PLEASE TELL ME HOW TO ATTAACH FILE INTO THE FORUM

THANK YOU

Last edited: Sep 2, 2008
2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
There is an error in yuor values, the input current is greater than the output current, i think it should be in uA rather than mA.

3. ### muni Thread Starter Active Member

Jul 29, 2008
45
0

sir in that case plase consider your own values and can u give me formula how to calculate fan out for this ic

4. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Fanout is defined as the number of inputs an output can drive. Did you Google fanout?

5. ### muni Thread Starter Active Member

Jul 29, 2008
45
0
sir i've searched through google i'm getting same threads as searcg results. with wikipedia i'm getting this.

The fan-out is simply the number of inputs that can be connected to an output before the current required by the inputs exceeds the current that can be delivered by the output while still maintaining correct logic levels. The current figures may be different for the logic zero and logic one states and in that case we must take the pair that give the lower fan-out. This can be expressed mathematically as
by applying values -0.4 mAmp/ 20 mAmp.
even then answer doesn't match with any of the choices.

request for new look
thank you sir

6. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
The Wikipedia equation includes the floor function. Do you understand what this is?

7. ### muni Thread Starter Active Member

Jul 29, 2008
45
0
no sir i haven't seen the floor functions.

sir i don't know how to upload a file itno the forum else i can show u the calculation. thank you sir . i'm going through floorfunctions

8. ### muni Thread Starter Active Member

Jul 29, 2008
45
0
sir i went through floor functions. but hardly i could understnad any thiing. sorry sir.

in this particular Q there are no calculations to carry on but i think i need right formula to solve it

9. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
IIH max=20uA, not 20mA, as you stated.

Below is a schematic which illustrates how fanout is calculated.

File size:
20.9 KB
Views:
43
10. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Another factor that makes a firm answer impossible, is that the chip might be driving another logic family (like 74LSxx) and the input requirements will be different, directly affecting fanout.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Don't you think we can assume that the values for IOH, IIH, IOL, and IIL given are intended to bracket the problem? Let's not confuse our OP any more than he/she is already.

12. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Point taken - I'm just too aware of finding that the book didn't cover quite all the situations....