LNK362-364
Optocoupler
2. Maximumdraincurrent–Atmaximumambienttemperature,
maximum input voltage and peak output (overload) power,
verify drain current waveforms for any signs of transformer
saturation and excessive leading-edge current spikes at
startup. Repeat under steady state conditions and verify that
theleading-edgecurrentspikeeventisbelowILIMIT(MIN) atthe
endofthetLEB(MIN). Underallconditions, themaximumdrain
current should be below the specified absolute maximum
ratings.
3. Thermal Check – At specified maximum output power,
minimuminputvoltageandmaximumambienttemperature,
verify that the temperature specifications are not exceeded
for LinkSwitch-XT, transformer, output diode and output
capacitors. Enough thermal margin should be allowed for
part-to-part variation of the RDS(ON) of LinkSwitch-XT as
specifiedinthedatasheet.Underlowline,maximumpower,
a maximum LinkSwitch-XT SOURCE pin temperature of
105 °C is recommended to allow for these variations.
Place the optocoupler physically close to the LinkSwitch-XT to
minimize the primary-side trace lengths. Keep the high current,
high voltage drain and clamp traces away from the optocoupler
to prevent noise pick up.
Output Diode
For best performance, the area of the loop connecting the
secondary winding, the output diode and the output filter
capacitor should be minimized. In addition, sufficient copper
area should be provided at the anode and cathode terminals
of the diode for heat sinking. A larger area is preferred at the
quiet cathode terminal. A large anode area can increase high
frequency radiated EMI.
Quick Design Checklist
As with any power supply design, all LinkSwitch-XT designs
should be verified on the bench to make sure that component
specificationsarenotexceededunderworst-caseconditions.The
following minimum set of tests is strongly recommended:
Design Tools
Up-to-date information on design tools can be found at the
Power Integrations web site: www.powerint.com.
1. Maximum drain voltage – Verify that VDS does not exceed
650Vatthehighestinputvoltageandpeak(overload)output
power. The 50 V margin to the 700 V BVDSS specification
gives margin for design variation, especially in Clampless
designs.
C
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