LNK562-564
Y Capacitor
2. Maximum drain current – At maximum ambient
temperature, maximum input voltage and peak output
(overload) power, verify drain current waveforms for any
signs of transformer saturation and excessive leading-edge
currentspikesatstartup.Repeatundersteadystateconditions
andverifythattheleading-edgecurrentspikeeventisbelow
ILIMIT(MIN) at the end of the tLEB(MIN). Under all conditions, the
maximum DRAIN current should be below the specified
absolute maximum ratings.
The placement of the Y capacitor should be directly from the
primary input filter capacitor positive terminal to the common/
return terminal of the transformer secondary. Such a placement
will route high magnitude common-mode surge currents away
from the LinkSwitch-LP device. Note: If an input pi (C, L, C)
EMIfilterisused, thentheinductorinthefiltershouldbeplaced
between the negative terminals on the input filter capacitors.
Output Diode
3. Thermal Check – At specified maximum output
power, minimum input voltage and maximum ambient
temperature, verify that the temperature specifications
are not exceeded for LinkSwitch-LP, transformer, output
diode and output capacitors. Enough thermal margin
should be allowed for part-to-part variation of the RDS(ON) of
LinkSwitch-LPasspecifiedinthedatasheet.Underlowlineand
maximumpower,amaximumLinkSwitch-LPSOURCEpin
temperature of 100 °C is recommended to allow for these
variations.
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-LP 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. A 50 V margin to the 700 V BVDSS specification
gives margin for design variation, especially in Clampless
designs.
F
7
10/05
POWERINT [ Power Integrations ]
