viper20b STMicroelectronics, viper20b Datasheet - Page 14

• Manufacturer Part Number: viper20b
• Description: Smps Primary I.c.
• Manufacturer: STMicroelectronics

VIPer20B / VIPer20BSP
schematic to be adapted depending the specific
needs. If the proposed schematic is used, the
pulse duration must be kept at a low value (500ns
is sufficient) for minimizing consumption. The
optocoupler must be able to provide 20mA
through the optotransistor.
PRIMARY PEAK CURRENT LIMITATION
The primary I
effect, the output power can be limited using the
simple circuit shown in figure 18. The circuit
based on Q1, R
the COMP pin in order to limit the primary peak
current of the device to a value:
I
14/17
Figure 15: Typical Compensation Network
Figure 17:External Clock Synchronization
DPEAK
V
COMP
H
OSC
ID
DPEAK
1
10 k
13V
0.5
VDD
and R
+
-
current and, as resulting
C2
2
VIPer
COMP SOURCE
OSC
clamps the voltage on
F C00452
R1
C1
13V
VDD
DRAIN
-
+
VIPer
COMP SOURCE
FC00 472
DRAIN
where:
V
The suggested value for R
220K .
OVER-TEMPERATURE PROTECTION:
Over-temperature protection is based on chip
temperature sensing. The minimum junction
temperature at which over-temperature cut-out
occurs is 140
The device is automatically restarted when the
junction temperature decreases to the restart
temperature threshold that is typically 34
the shutdown value (see figure 6).
Figure 16: Slope Compensation
Figure 18:Current Limitation Circuit Example
COMP
0.6
R2
C1
x
o
OSC
C while the typical value is 160
R
R1
R3
Q1
1
R
13V
VDD
2
R
OSC
2
+
-
R1
R2
13V
VDD
VIPer
C2
COMP SOURCE
+
1
-
+R
FC 00 482
VIPe r
COMP SOURCE
2
Q1
C3
DRAIN
is in the range of
FC00462
DRAIN
o
C below
o
C.