AN578 APPLICATION NOTE POWER CROSSING BEHAVIOUR OF LINE CARD PROTECTION INTRODUCTION The purpose of this document is to explain the behaviour of LCP 150S/1511/1512 devices during the coupling between a telecommunication line and a mains line. TEST DIAGRAM Figure 1 shows the test diagram. The mains 220 V 50 Hz is applied to the test assembly through an isolation transformer. A relay driven by a mono-pulse generator allows the conducting time to be adjusted. The current through the device is adjusted by a series resistor. Figure 1. Test Diagram RELAY 0 to 4K 1/1 Line A 220V LCPxxx 50Hz GND ISOLATION G AT E TRANSFORMER + - POWER SUPPLY 48V MEASUREMENTS During the tests three kinds of behaviour occur: a) As shown in Figure 2 the device acts as a clamping device (non-firing) due to the small value of the current which never exceeds the latching current of the structure. May 2004 REV. 2A - 3601 1/5 AN578 Figure 2. Voltage and current for a non-firing device 0V -48V 0A Voltage between line A and GND. Current through the line A b) In the second operating region the LCPxxx fires and the piece under test is still functional after 15 minutes. – Figure 3.1 shows the start of the firing (the peak of the current wave through the device is just over the latching limit). – Figure 3.2 the amplitude of the current wave through the device is greater than in the precedent case, so the device is well fired after a few hundred microseconds. c) In the third operating region the device has been destoyed in a time depending on the current through the LCPxxx. Figure 3. Equivalent circuit of both driver and receiver adjacent lines 0V -48V 0V -48V 2/5 3.1 With I slightly higher than I latch. 3.2 With I considerably higher than I latch. AN578 ANALYSIS Table 1. Operating Region Definition OPERATING REGION LCP 150 LCP 1512 LCP 1511 A/clamping 0 to 70 mA * O to 70 mA * O to 70 mA * B/non destructive region 0.07 to 2 A * 0.07 to 1.2A* 0.07 to 0.8A * Over 2 A * Over 1.2 A * Over 0.8 A * C/destructive region * RMS current Table 1 shows the range of the three operating regions, while Figure 4, which illustrates region C, allows us to determine the destruction time limit of each device versus the current through the structure (RMS current at 25°C). Figure 4. Characteristics of Region C (With Vgate = -48 V) LCP150 / 1511 / 1512 I(Arms) 20 10 5 2 1 0,5 0,5 1 2 5 10 20 50 100 t(S) LCP150 LCP1512 LCP1511 CONCLUSION Figure 4: The devices in the LCPxxx family have common characteristics, divided into three regions: a) Clamping mode, still functional after 15 minutes b) Crowbar mode (firing) still functional after 15 minutes of test at 25°C c) Crowbar mode, with a destruction time defined by Figure 4. The given curves enable the appropriate series elements to be chosen, for example a PTC device. 3/5 AN578 REVISION HISTORY Table 2. Revision History 4/5 Date Revision Description of Changes March-1993 1 First Issue 3-May-2004 2 Stylesheet update. No content change. AN578 Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2004 STMicroelectronics - All rights reserved STMicroelectronics GROUP OF COMPANIES Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States www.st.com 5/5