MM74C908N Fairchild Semiconductor, MM74C908N Datasheet - Page 4

• Manufacturer Part Number: MM74C908N
• Description: IC DRIVER RELAY DUAL 30V 8-DIP
• Manufacturer: Fairchild Semiconductor
• Series: 74Cr

Specifications of MM74C908N

• Logic Type: Relay Driver
• Supply Voltage: 3 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Supply Voltage (min): 3 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Number Of Bits: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 74C908; 74C908N

www.fairchildsemi.com
Power Considerations
Calculating Output “ON” Resistance (R
The output “ON” resistance, R
tion temperature, T
and T
where T
and P
device. P
to leakage currents, internal capacitance, switching, etc.)
which are insignificant when compared to the power dissi-
pated in the outputs. Thus, the output power term defines
the allowable limits of operation and includes both outputs,
A and B. P
where I
The average power dissipation, P
duty cycle:
where the duty cycle is the % time in the current source
state. Substituting equations (1) and (5) into (2) yields:
[I
simplifying:
Applications
(See AN-177 for applications)
OA
R
T
P
V
P
I
T
OB
J
(4)
J
D
L
DAV
ON
2
is the load voltage.
2
(Duty Cycle
J
DAV
T
R
T
is given by:
O
I
A
OA
A
A
ON
9 (T
DAV
is the output current, given by:
I
OA
D
2
(Duty Cycle
ambient temperature,
is the average power dissipated within the
R
P
is given by:
2
J
ON
JA
DAV JA
consists of normal CMOS power terms (due
R
ON
[9 (T
25) (0.008)
A
)
I
(Duty Cycle
J
OB
, and is given by:
J
,: (2)
I
2
OB
B
R
25) (0.008)
)
2
ON
(Duty Cycle
, (3)
9:
ON
A
)
, is a function of the junc-
DAV
(1)
JA
(5)
9]: (6a)
, is a function of the
B
)]
thermal resistance,
L
18 )
4
Equations (1), (4), and (6b) can be used in an iterative
method to determine the output current, output resistance
and junction temperature.
For example, let V
V
Duty Cycle
Assuming R
and
and R
L
9(52.6
0V, T
ON
25) (0.008)
A
B
9 (T
ON
75%.
25 C,
J
11 , then:
CC
25) (0.008)
JA
15V, R
9
110 C/W, Duty Cycle
11
LA
9
100 , R
LB
100 ,
A
50%,