AN453 Application note TDE1897C, TDE1897R, TDE1898C and TDE1898R in extreme overload conditions Introduction The purpose of this document is to provide the circuit designer with some insight into how the TDE1897C, TDE1897R, TDE1898C and TDE1898R devices behave in extreme overload conditions. Although the conditions may range outside the limits of the guaranteed performances described in the device datasheet, erroneous connections during the installation phase may occur and momentarily create such conditions. The performed tests confirm the extreme ruggedness of this device and its ability to overcome the accidental overload. The TDE1897C, TDE1897R, TDE1898C and TDE1898R are monolithic intelligent power switch (IPS) in high-side configuration made in BCD technology (see Figure 1). They can drive resistive and inductive loads such as lamps, relays, electrovalves and so on. An internal voltage clamping diode to +VS creates, in inductive loads, a fast demagnetization path with no external components. Suitable for industrial applications, the device operates in the 18- to 35 V supply range, delivering output currents up to 500 mA. In typical applications, it can drive up to 1 or 1.5 H load coils (48 to 60 Ω typical associated resistance). Figure 1. December 2008 Block diagram Rev 3 1/8 www.st.com Contents AN453 Contents 1 Overload conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Overload operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Measurements and calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2/8 AN453 1 Overload conditions Overload conditions To investigate how the TDE1897C, TDE1897R, TDE1898C and TDE1898R behave in extreme inductive overload conditions, which can occur when too big a load is connected to the device output, tests have been performed in bias conditions that lead the device to function out of the operatives and rated limits specified in the datasheet. The test conditions (depicted in Figure 2) are the following: VS = +24 V, IO = internal limited, Tamb = 25 °C, L = 1.4 H (non saturating), RL = 12 Ω, Vi = 2 V (Vih)(a), Tj = from Θ Lim-TH to Θ Lim and above(b). Figure 2. Inductive load equivalent circuit and demagnetization cycle waveforms a. The input signal asks for a permanent "on" state. b. Θ Lim and TH = thresholds of intervention and hysteresis of the internal thermal protection circuit. 3/8 Overload operation 2 AN453 Overload operation Due to the internal limitation (ISC), the output current (IO) is not limited by the load (VS/Rl = 2 A, ISC ≤ 1.5 A) but by the device itself. As soon as the current reaches ISC, the IPS goes out of the minimum resistance state and increases its voltage drop so that IO = ICS. The silicon temperature of the DUT increases rapidly up to the thermal protection threshold value (Θ Lim) and such protection tries to cut-off the output DMOS. The output’s turn-off forces the demagnetization cycle, which discharges the energy of the inductive load (to VS) through the device. Because of the higher energy in the magnetic load and the higher peak power (see Note 1), the higher-clamped current value (ISC) produces, during demagnetization, more stress conditions. During the "on" state, the power (Pdon) on the DUT (see the 225 msec. interval in Figure 3) is defined by the IO (ISC) and Rl values. The chip temperature rapidly increases and reaches the upper thermal protection threshold value (Θ Lim). At that moment the protection is triggered on, inducing a switch-off of the output channel. Due to the inductive component in the load, you must wait for the associated demagnetization phase (some 50 msec. after the 225 msec. interval) to see the actual switch-off. The DUT then starts to cool down staying in the off state until the chip temperature goes down to a lower thermal threshold value (Θ Lim-TH). When this lower limit is attained, the thermal protection circuit withdraws itself and the chip resumes its normal functions and restarts another cycle. In fact, its input will have been connected permanently to a voltage level of more than 2 V, meaning a continuous request for conduction. A new overload cycle begins and a periodic repetition of the following: ● Load charging ● Current limitation ● Over-temperature and demagnetization ● Cooling down in the off state. It can be noted that, for given thermal parameters (Zth, thermal protection levels and hysteresis), differences in Pdon affect only the "TON" and "TOFF" duration and ratio of such periodic repetitions. Note: 4/8 1 During the demagnetization phase, the power dissipated inside the IPS chip is: IO(t) * VCL. IO (t) decays to zero from ISC, VCL is set by the IPS itself to approximately 50 V. AN453 3 Measurements and calculations Measurements and calculations For a typical TDE1897C or TDE1897R sample in Minidip package (see Figure 3) in "thermal" periodic repetition, the current (self-limited region) is limited to 1.1 A and the voltage across the DUT is equal to 10.8 V for 225 msecs of "on" time. The energy dissipated on the DUT in the demagnetization cycle is equal to 1.28 J. ● The repetition cycle rate is equal to 0.27 Hz (t = 3.7 seconds) ● Pdon (average) = 1.1 A × 10.8 V × 0.225 sec/3.7s = 0.72 W ● Pdem (average) = 1.28 J × 0.27 cycles/s = 0.346 W. Adding the small power dissipated to operate the quiescent current and for IO(t)^2*RON in the load charging region, the total power P(tot) of 1.1 W is considered a realistic value. Minidip (on the test-socket) Rthj-amb is approximately 85 °C/W, which leads the average temperature in the hot region of the chip to 115/120 °C (the chip is not homogeneous in temperature; higher temperatures are reached, during dissipation, in the area of the output DMOS). Figure 3. TDE1897R or TDE1897C in Minidip Figure 4. package output voltage (CH2) and output current (CH1) vs. time in thermal periodic repetition TDE1897R or TDE1897C in Minidip package output current and temperature in the test point vs. time 5/8 Conclusion 4 AN453 Conclusion The complex protection system of the TDE1897C, TDE1897R, TDE1898C and TDE1898R also prove effective in extreme overload conditions. Although the behavior of such devices in these conditions cannot be guaranteed due to the high temperatures that accelerate the intrinsic ageing mechanism, the tests performed show that there is a lot of margin beyond the limits guaranteed in the device datasheet. These tests also show that it is quite likely that such devices will survive non-permanent overloads like the ones that can occur in practice during the installation or modification of an industrial control system. 6/8 AN453 5 Revision history Revision history Table 1. Document revision history Date Revision Changes December 2003 1 Initial release July 2005 2 – Updated the layout look & feel. – Changed title 10-Dec-2008 3 – Document reformatted. No content change. – Obsoleted SIP9 package reference 7/8 AN453 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectual property contained therein. UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZED ST REPRESENTATIVE, ST PRODUCTS ARE NOT RECOMMENDED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY, DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. ST PRODUCTS WHICH ARE NOT SPECIFIED AS "AUTOMOTIVE GRADE" MAY ONLY BE USED IN AUTOMOTIVE APPLICATIONS AT USER’S OWN RISK. Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any liability of ST. ST and the ST logo are trademarks or registered trademarks of ST in various countries. Information in this document supersedes and replaces all information previously supplied. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners. © 2008 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 of America www.st.com 8/8