TOP245F datasheet(27/52 Pages) POWERINT

27 / 52 page

TOP242-250

1/02

Key Application Considerations

TOPSwitch-II vs. TOPSwitch-GX

Table 4 compares the features and performance differences

between TOPSwitch-GX and TOPSwitch-II. Many of the new

features eliminate the need for additional discrete components.

Other features increase the robustness of design allowing cost

savings in the transformer and other power components.

Function

TOPSwitch-II

TOPSwitch-GX

Figures

TOPSwitch-GX 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

• Reduces or eliminates output

overshoot

External Current Limit

N/A*

Programmable

11,20,21,

• Smaller transformer

100% to 30% of

24,25,27,

• Higher efficiency

default current

28,34,35,

• Allows power limiting (constant over-

limit

38,39

load power independent of line

voltage

• Allows use of larger device for lower

losses, higher efficiency and smaller

heatsink

MAX

67%

78%

• Smaller input cap (wider dynamic

range)

• Higher power capability (when used

with RCD clamp for large V

OR)

• Allows use of Schottky secondary

rectifier diode for up to 15 V output

for high efficiency

Line Feed Forward with N/A*

78% to 38%

7,11,17,

• Rejects line ripple

MAX Reduction

26,27,28,

31,40

Line OV Shutdown

N/A*

Single resistor

11,17,19,

• Increases voltage withstand cap-

programmable

26,27,28,

ability against line surge

31,33,40

Line UV Detection

N/A*

Single resistor

11,17,18,

• Prevents auto-restart glitches

programmable

26,27,28,

during power down

31,32,40

Switching Frequency

100 kHz ±10%

132 kHz ±6%

13,15

• Smaller transformer

• Below start of conducted EMI limits

Switching Frequency

N/A*

66 kHz ±7%

14,15

• Lower losses when using RC and

Option (Y, R and F

RCD snubber for noise reduction in

Packages)

video applications

• Allows for higher efficiency in

standby mode

• Lower EMI (second harmonic below

150 kHz)

Frequency Jitter

N/A*

±4 kHz@132 kHz 9,46

• Reduces conducted EMI

±2 kHz@66 kHz

Frequency Reduction

N/A*

At a Duty Cycle

• Zero load regulation without dummy

below 10%

load

• Low power consumption at no load

Table 4. Comparison Between TOPSwitch-II and TOPSwitch-GX. (continued on next page) *Not available

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