TOP245F datasheet(32/54 Pages) POWERINT

32 / 54 page

Rev. R 10/20

TOP242-250

www.power.com

In Figures 47, 48 and 49, a narrow trace is shown between

the output rectifier and output filter capacitor. This trace

acts as a thermal relief between the rectifier and filter

capacitor to prevent excessive heating of the capacitor.

Quick Design Checklist

As with any power supply design, all TOPSwitch-GX

designs should be verified on the bench to make sure that

components specifications are not exceeded under worst

case conditions. The following minimum set of tests is

strongly recommended:

1. Maximum drain voltage – Verify that peak V

DS does not

exceed 675 V at highest input voltage and maximum

overload output power. Maximum overload output

power occurs when the output is overloaded to a level

just before the power supply goes into auto-restart (loss

of regulation).

2. Maximum drain current – At maximum ambient

temperature, maximum input voltage and maximum

output load, verify drain current waveforms at start-up

for any signs of transformer saturation and excessive

leading edge current spikes. TOPSwitch-GX has

a leading edge blanking time of 220 ns to prevent

premature termination of the ON-cycle.Verify that the

leading edge current spike is below the allowed current

limit envelope (see Figure 52) for the drain current

waveform at the end of the 220 ns blanking period.

3. Thermal check – At maximum output power, minimum

input voltage and maximum ambient temperature, verify

that temperature specifications are not exceeded for

TOPSwitch-GX, transformer, output diodes and output

capacitors. Enough thermal margin should be allowed

for the part-to-part variation of the R

DS(ON) of TOPSwitch-

GX, as specified in the data sheet. The margin required

can either be calculated from the tolerances or it can

be accounted for by connecting an external resistance

in series with the DRAIN pin and attached to the same

heat sink, having a resistance value that is equal to the

difference between the measured R

DS(ON) of the device

under test and the worst-case maximum specification.

Design Tools

For a discussion on utilizing TOP248, TOP249

and TOP250 in forward converter configurations,

please refer to the TOPSwitch-GX Forward Design

Methodology Application Note.

Up-to-date information on design tools can be found at the

Power Integrations website: www.power.com

- DC

Out

PI-2734-043001

Safety Spacing

Y1-

Capacitor

Solder Side

Component Side

Opto-

coupler

Output Filter Capacitors

Maximize hatched copper

areas (

) for optimum

heat sinking

TOP VIEW

Input Filter

Capacitor

R1a - 1c

PRI

SEC

BIAS

TOPSwitch-GX

Figure 49. Layout Considerations for TOPSwitch-GX using R Package.

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