ML4818
UNDER-VOLTAGE LOCKOUT
On power up, when V
CC
is below 16V, the IC draws very
little current (1.1mA typ.) and V
REF
is disabled. When V
CC
rises above 16V, the IC becomes active and V
REF
is
enabled and will stay in that condition until V
CC
falls
below 10.2V. (see Figure 12).
INHIBIT
OUTPUTS
0.555"
1
2
3
24
23
22
21
20
19
18
17
16
15
14
13
I
I
–
+
4V
TO LOGIC
CIRCUITS
5V
V
REF
24
4
5
POWER
DOWN
I
6
7
8
9
9V
V
CC
+
–
INTERNAL
BIAS
I
10
11
12
20
Figure 12. Under-Voltage Lockout and
Reference Circuits.
70
68
66
SUPPLY CURRENT (mA)
64
62
60
58
56
54
52
50
–75
Figure 14. PC Board Copper Area Used as a Heat Sink.
50
40
30
20
–25
25
75
125
175
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
TEMPERATURE
I : HEAT SINK DIMENSION (INCHES)
Figure 13. Supply Current vs. Temperature (°C).
Figure 15.
θ
JA
as a Function of I (see figure 15).
THERMAL INFORMATION
The ML4818 is offered in a Power DIP package. This
package features improved thermal conduction through
the leadframe. Much of the heat is conducted through the
center 4 grounded leads. Thermal dissipation can be
improved with this package by using copper area on the
board to function as a heat sink. Increasing this area can
reduce the
θ
JA
(see figures 14 and 15), increasing the
power handling capability of the package. Additional
improvement may be obtained by using an external heat
sink (available from Staver).
APPLICATIONS
The application circuit shown in Figure 16 features the
ML4818 in a primary-side controlled voltage mode
application with voltage feed-forward. Input voltage is
rectified 120VAC (nominal). Feed-forward is provided by
the RAMP pin via the resistor connected to the high
voltage input. Current is sensed through sense transformer
T4.
9
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
