1. Electrical Calculations
Sample Calculations 2
Electrical Calculations
with Solutions
Last Mod: January 2008
©Paul R. Godin

2. Calculations
Calculate the values for each circuit using values from the specification sheets.
Use the TI specification sheets for TTL
Use the OnSemi Specification sheets for CMOS

3. Calculate Propagation Delay
74S04 to 7432
7432 to 74LS02
74LS86A to 7408

4. Calculate Fanout 74LS02 to 74LS86A 74LS32 to 7400 74LS02 to 7400

5. Calculate Power Calculate power dissipation for the following device:b
Where:
a: output high
b: output low
c: output at 25% DC
d: output at 50% DC
74S32 c d

6. Calculate Power Calculate power dissipation for the following device:
Where:
One output = 80% DC
One output = high
All other outputs = low
74LS04

7. Calculate Noise Margin
74S04 to 7432
7432 to 74LS02
74LS02 to 74S08
74S08 to 74LS32

8. Solutions

9. Answers (in RED) tPLH + tPLH = 4.5S + 15S = 19.5S
tPHL + tPHL = 5S + 22S = 27S
tPLH + tPHL = 15S + 15S = 30S
tPHL + tPLH = 22S + 15S = 37S
tPLH + tPLH = 30S + 27S = 57S
tPHL + tPHL = 22S + 19S = 41S
tPLH + tPLH = 23S + 27S = 50S
tPHL + tPHL = 17S + 19S = 36S

10. Answers (in RED) 0.4mA / 40A = 10 8mA / 0.8mA = 10 …..Fanout = 10

11. Answers (RED) a: ¼  32mA = 8mA b: ¼  68mA = 17mA
c: ¼  [(0.2532mA)+(0.7568mA)]= 14.75mA
d: ¼  [(0.5032mA)+(0.5068mA)]= 12.5mA
Total current (Icc) = 52.25mA
Total power (Pd) = 5V  52.25mA = mW

12. Answers (RED) a: 1/6  [(0.802.4mA)+(0.206.6mA)]= 0.54mA
b: 1/6  2.4mA = 0.4mA
c: 4/6  6.6mA= 4.4mA
Total current (Icc) = 5.34mA
Total power (Pd) = 5V  5.34mA = 27.6mW
Note: There are 6 gates in this monolithic device.

13. Answers (RED) VOH – VIH = 2.7V – 2V = 0.7V = VnH
VIL – VOL = 0.5V – 0.8V = 0.3V = VnL
VOH – VIH = 2.4V – 2V = 0.4V = VnH
VIL – VOL = 0.4V – 0.8V = 0.4V = VnL

14. End
Paul R Godin
gmail.com