AN2482 Datasheet, PDF (1/18 Pages) STMicroelectronics – The purpose of this document

AN2482
Application note
PCLT (Programmable current limited termination)
Introduction
The purpose of this document is:
■ To describe the PCLT behavior (refer also to data sheet)
■ To give useful recommendations to achieve robust PCLT designs regarding EMI test
(IEC 61000-4-5 and 4-4)
■ To give information on thermal behavior of PCLT in its application
■ To describe the demonstration board and recommendations for use
Contents
1
PCLT Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 External biasing resistor settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Protection against reverse polarity of power supply . . . . . . . . . . . . . . . . . 5
1.5 Opto-coupler and CMOS modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
Thermal dissipation calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 Normal forward polarity of all inputs case . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Reverse polarity on a single input case . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 R_TH adjustment with PCB area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Experimental T_j measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
Unisolated AS-interface bus application . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Application overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Isolation of the sensor section and the supply from data/supply bus . . . . 10
3.3 Un-isolated connection of the PCLT with AS-Interface controller . . . . . . . 11
4
Electromagnetic compatibility (EMC) requirements . . . . . . . . . . . . . . 12
5
Demo board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1 Description of the PCLT-2A demo board . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2 Operating instructions of the PCLT-2A demo-board . . . . . . . . . . . . . . . . . 15
6
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
February 2007
Rev 1
1/18
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