TOP232-234
Key Application Considerations
TOPSwitch-FX vs. TOPSwitch-ll
Table 3 compares the features and performance differences
between TOPSwitch-FX and TOPSwitch-II. Many of the new
features eliminate the need for costly discrete component.
Other features increase the robustness of design allowing cost
savings in the transformer and other power components.
Function
TOPSwitch-II TOPSwitch-FX Figures Advantages
Soft-Start
N/A*
10 ms
• Limits peak current and voltage
component stresses during start-up
• Eliminates external components
used for soft-start in most
applications
• Minimizes output overshoot
External Current Limit
N/A*
67%
Programmable
100% to 40% of
default current
limit
8, 17,
• Smaller transformer
18, 21, • Higher efficiency
22
4
• Allows tighter power limit
during output overload conditions
DCMAX
78%
• Smaller input cap (wider dynamic
range)
• Higher power capability (when used
with RCD clamp for large VOR)
• Allows use of Schottky secondary
rectifier diode for up to 15 V output
for high efficiency
Line Feed Forward with N/A*
DCMAX Reduction
78% to 38%
4, 8, 14, • Rejects line ripple
23
• Increases transient and surge
voltage withstand capability
Line OV Shutdown
Line UV Detection
Switching Frequency
N/A*
Single resistor
programmable
8, 14,
16, 23
• Increases voltage withstand cap-
ability against line surge
N/A*
Single resistor
programmable
5, 8, 14, • Prevents auto-restart glitches
15, 23
during power down
100 kHz 10%
132 kHz 7%
10
• Smaller transformer
• Fundamental below 150 kHz for
conducted EMI
Switching Frequency
Option (TO-220 only)
N/A*
66 kHz 7%
11, 12 • Lower losses when using RC and
RCD snubber for noise reduction in
video applications
• Allows for higher efficiency in
standby mode
• Lower EMI (second harmonic below
150 kHz)
Frequency Jitter
Cycle Skipping
N/A*
N/A*
4 kHz@132 kHz 6, 28
2 kHz@66 kHz
• Reduces conducted EMI
At DCMIN (1.5%)
4
• Zero load regulation without dummy
load
• Low power consumption at no load
*Not available
Table 3. Comparison Between TOPSwitch-II and TOPSwitch-FX. (continued on next page)
B
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PAM [ POWER ANALOG MICOELECTRONICS ]
