TOP243 View Datasheet(PDF) - Power Integrations, Inc

Part Name

Description

Manufacturer

TOP243

Extended power, design elexible, integrated off-line switcher

Power Integrations, Inc 

TOP242-250

Function

TOPSwitch-FX

TOPSwitch-GX

TOPSwitch-GX Advantages

P/G Package Current Identical to Y

Limits

packages

TOP243P or G and

TOP244P or G internal

current limits reduced

Y/R/F Package Current 100% (R and F

Limits

package N/A*)

90% (for equivalent RDS ) (ON)

Thermal Shutdown

125 °C min.

130 °C min. 75 °C

70 °C hysteresis hysteresis

Maximum Duty Cycle 90 µA

Reduction Threshold

60 µA

Line Under-Voltage

Negative (turn-off)

Threshold

Soft-Start

N/A*

40% of positive (turn-on)

threshold

10 ms (duty cycle) 10 ms (duty cycle + current

limit)

• Matches device current limit to

package dissipation capability

• Allows more continuous design to

lower device dissipation (lower RMS

currents)

• Minimizes transformer core size

• Optimizes efficiency for most

applications

• Allows higher output powers in

high ambient temperature

applications

• Reduces output line frequency

ripple at low line

• DMAX reduction optimized for

forward design

• Provides a well defined turn-off

threshold as the line voltage falls

• Gradually increasing current limit

in addition to duty cycle during soft-

start further reduces peak current

and voltage

• Further reduces component

stresses during start up

Table 5 (cont). Comparison Between TOPSwitch-FX and TOPSwitch-GX. *Not available

TOPSwitch-GX Design Considerations

Power Table

Data sheet power table (Table 1) represents the maximum practi-

cal continuous output power based on the following conditions:

TOP242 to TOP246: 12 V output, Schottky output diode, 150 V

reflected voltage (V ) and efficiency estimates from curves con-

OR

tained in application note AN-29. TOP247 to TOP250: Higher

output voltages, with a maximum output current of 6 A.

For all devices, a 100 VDC minimum for 85-265 VAC and

250 VDC minimum for 230 VAC are assumed and sufficient heat

sinking to keep device temperature ≤100 °C. Power

levels shown in the power table for the R package device

assume 6.45 cm2 of 610 g/m2 copper heat sink area in an

enclosed adapter, or 19.4 cm2 in an open frame.

TOPSwitch-GX Selection

Selecting the optimum TOPSwitch-GX depends upon required

maximum output power, efficiency, heat sinking constraints

and cost goals. With the option to externally reduce current

limit, a larger TOPSwitch-GX may be used for lower power

applications where higher efficiency is needed or minimal heat

sinking is available.

Input Capacitor

The input capacitor must be chosen to provide the minimum DC

voltage required for the TOPSwitch-GX converter to maintain

regulation at the lowest specified input voltage and maximum

output power. Since TOPSwitch-GX has a higher DCMAX than

TOPSwitch-II, it is possible to use a smaller input capacitor.

For TOPSwitch-GX, a capacitance of 2 µF per watt is possible

for universal input with an appropriately designed transformer.

Primary Clamp and Output Reflected Voltage V

OR

A primary clamp is necessary to limit the peak TOPSwitch-GX

drain to source voltage. A Zener clamp requires few parts and

takes up little board space. For good efficiency, the clamp

Zener should be selected to be at least 1.5 times the output

reflected voltage V as this keeps the leakage spike conduc-

OR

tion time short. When using a Zener clamp in a universal input

application, a VOR of less than 135 V is recommended to allow

for the absolute tolerances and temperature variations of the

Zener. This will ensure efficient operation of the clamp circuit

and will also keep the maximum drain voltage below the rated

breakdown voltage of the TOPSwitch-GX MOSFET.

29 H

9/02

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