EPR-16 datasheet(28/36 Pages) POWERINT

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EPR-16 - LinkSwitch 2.75 W Charger/Adapter

17-May-04

11 Appendix B – LNK520P in the High-Side Configuration

11.1 Introduction

In applications with looser CV/CC limits, the lower cost LinkSwitch LNK520P can be used

in the high-side configuration, which may be attractive since the internal MOSFET drive

has been optimized, typically reducing radiated EMI by 6 dB to 10 dB. This appendix

details the changes necessary to replace U1 from a LNK501 to a LNK520 device. In

addition, resultant changes in the output characteristic, efficiency, no-load consumption

and radiated EMI are presented.

11.2 Comparison of LNK501 and LNK520

The LNK501 was designed for use in a high-side configuration, using the VOR across the

primary winding to provide output sensing and feedback. Since the feedback signals

differ, the internal control characteristics of the LNK501/LNK520 have therefore been

specifically optimized for high-side/low-side operation, respectively. The LNK520 was

designed for use in a low-side configuration, using an auxiliary or bias winding to sense

the output and provide feedback. In addition, the LNK520 has a wider I2f data sheet

tolerance than the LNK501.

When using the LNK520 device in the high-side configuration, the output voltage tends to

be higher at no-load and the CC region of the output characteristic is less linear, the

output current increasing as the output voltage reduces. The wider I2f specification of the

LNK520 increases the CC tolerance from approximately

±20% to at least ±25%.

In many applications, for example replacing a linear supply, the wider output tolerances

and linearity are acceptable.

The LNK520 has one key advantage over the LNK501. The internal MOSFET drive has

been optimized to reduce high frequency radiated EMI. Typically a 6 dB to 10 dB

improvement in radiated (>30 MHz) EMI performance is seen compared with the

LNK501.

Page 28 of 36

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EPR-16 Fiches technique(PDF) 28 Page - Power Integrations, Inc.