TOP250F-TL datasheet(32/52 Pages) POWERINT

32 / 52 page

TOP242-250

12/04

Quick Design Checklist

As with any power supply design, all TOPSwitch-GX designs

should be veriﬁed on the bench to make sure that components

speciﬁcationsarenotexceededunderworstcaseconditions.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

occurswhentheoutputisoverloadedtoaleveljustbeforethe

power supply goes into auto-restart (loss of regulation).

2. Maximumdraincurrent–Atmaximumambienttemperature,

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

heatsink, 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 TOPSwitch-GX in a forward

converter conﬁguration, 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.powerint.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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