S P O C TM+ 1 2 V SPI Power Controller S h o r t C i r c u i t t o V S and Open Load Detection Application Note Rev. 1.0, 2013-09-25 Automotive Power SPOCTM+ 12V Short Circuit to VS and Open Load Detection Abstract 1 Abstract Note: The following information is given as a hint for the implementation of the device only and shall not be regarded as a description or warranty of a certain functionality, condition or quality of the device. This Application Note is intended to provide detailed application hints regarding the short circuit to VS detection of the SPOCTM+. Furthermore, an open load in OFF detection can be implemented with the use of an external resistor. General information about the SPI Power Controller can be found in the SPOCTM+ data sheets. 2 Introduction TM The SPOC + is a family of four, five or six channels high-side power switches, which are especially designed to control standard exterior front and rear lighting (either lamps or their LED equivalent) in automotive applications. Configuration and status diagnosis is done via SPI. Additionally, there is a current sense signal available for each channel that is routed via a multiplexer to one diagnostic pin. The following table is an overview of all products in SPOCTM+ 12V product family. Table 1 SPOCTM+ 12V product family overview Product Typical ON State Resistance at Tj = 25 °C (RDS(ON,typ)) Ext. driver capability BTS54220-LBA Channel 1, 4: 9 mΩ Channel 2, 3: 27 mΩ no BTS54220-LBE Channel 1, 4: 9 mΩ Channel 2, 3: 27 mΩ yes BTS54040-LBA Channel 1, 2, 3, 4: 39 mΩ no BTS54040-LBE Channel 1, 2, 3, 4: 39 mΩ yes BTS55032-LBA Channel 2, 3, 4: 39 mΩ Channel 1, 5: 110 mΩ no BTS56033-LBA Channel 2, 3, 4: 39 mΩ Channel 1, 5, 6: 110 mΩ no This document will show how to use the internal function of the Switch Bypass Monitor (SBM) to detect whether the output is connected via a low resistance to VS or not. For this short circuit to VS detection no external hardware is required. For the implementation of an open load in off detection an external resistor is required. Application Note 2 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Functionality of Switch Bypass Monitor (SBM) 3 Functionality of Switch Bypass Monitor (SBM) The Switch Bypass Monitor (SBM) is a part of the device logic, which evaluates the VDS voltage of the DMOS. There is only one SBM comparator on the device for all four, five or six channels. Thus, there is an additional multiplexer implemented, which connects the outputs of the channels to the SBM comparator. This multiplexer is also programmed by the current sense multiplexer bits of the diagnosis control register (DCR). For further details please refer to the datasheet. In case of a short circuit to VS and VDS < VDS(SB) the bit DCR.SBM indicates the short circuit to VS. This can be seen for OFF- (Table 2) and ON-state (Table 3). Table 2 SBM and Current Sense during OFF-state 1)2) Operation mode Current sense Bit DCR.SBM Normal operation Z 1 Short Circuit to GND Z 1 Over Temperature Z X Short Circuit to VS Z 0 Open Load Z X 1) Z = high impedance, potential depends on leakage currents and external circuit. X = undefined. 2) During OFF-state the bit dcr.SBMdepends on the potential at the output pin. The potential of the output pin depends in Open Load case on leakage currents. As a result, the bit DCR.SBM can be set either to “1” or “0” during an Open Load in OFF-state. Table 3 SBM and Current Sense during ON-state 1) Operation mode Current sense Bit DCR.SBM Normal operation IL / kILIS 0 Current limitation Z X Short Circuit to GND Z 1 Over Temperature Z X Short Circuit to VS < IL / kILIS 0 Open Load Z 0 1) Z = high impedance, potential depends on leakage currents and external circuit. X = undefined. Application Note 3 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Functionality of Switch Bypass Monitor (SBM) Use of SBM for Short Circuit to VS Detection 3.1 In case of a short circuit between one output pin and VS supply voltage a major part of the load current will flow through the short circuit. As a result, a lower current compared with the normal operation will flow through the DMOS of the SPOCTM+, which can be recognized at the current sense signal. In case of a current sense signal below the normal value, a software strategy is required to verify, whether an over temperature failure or a short circuit to VS leads to the low current sense signal. The following flow chart shows a possible way to implement a software strategy (see Table 4 for the SPI commands required by this sequence): Legend: Process Switch MUX to active channel n Decision Measure sense voltage VIS Yes Switch OFF channel Yes Store No No V IS > VIS(nom,max) ERR_MUX SC to VS or Open Load DCR.SBM = 1 Yes Store data No VIS < VIS(nom,min) Read DCR.SBM Yes Display Store VIS Switch MUX to next channel Over Load No ERR_MUX = n Channel n latched OFF (nretry reached) Yes No VIS < VIS( worstcase ) Under Load Open Load Figure 1 Decision flow chart to detect a Short Circuit to VS or a Channel Latch OFF (nretry reached) With this software routine it is possible to distinguish between short circuit to VS and over temperature. A complete differentiation between short circuit to VS and open load is not possible, because during open load the output potential depends on leakage currents. This can also cause a VDS voltage below VDS(SB). Therefore, the open load case may behave like a short circuit to VS. Application Note 4 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Functionality of Switch Bypass Monitor (SBM) For the determination of VIS(nom,min) and VIS(nom,max) please refer to the following two equations. VIS ( nom,min) = VIS( nom,max) = I nom,min kILIS,max I nom,max k ILIS,min ⋅ RIS ,min (1) ⋅ RIS,max (2) For the determination of VIS(worstcase) please refer to the following calculation. For example: The nominal load of channel 0 is a 21 W bulb. But it is also possible to put a 10 W or 5 W bulb into the socket of the 21 W load. Therefore, it might be interesting to recognize, if there is an open load or only a wrong bulb connected. The implementation of a VIS threshold with a value of 0.25 V for a sense resistor RIS = 2.7 kΩ is recommended. So, if the VIS voltage is below this threshold, then an Open Load failure is detected, otherwise a Under Load current caused the failure. The following calculation shows an example with typical values in bulb-mode, how the minimum sense voltage can be calculated. For channels with LED-mode higher accuracies can be achieved by switching into LED-mode. The switch into LED-mode can be done dynamically also when the channel is switched ON. Nominal current of a 10 W bulb: Inom,10W = 0.74 A Typical kILIS ratio for channel 2 in bulb-mode: kILIS = 2000 Typical sense resistor: RIS = 2.7 kΩ V IS = I nom ,10 W 0 .74 ⋅ R IS = ⋅ 2700 = 1 k ILIS 2000 (3) For the worst case calculation the following formula should be used: V IS ( worstcase ) = I nom ,10 W min ⋅ R IS ,min k ILIS ,max (4) The implemented threshold should be below this value. Application Note 5 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Functionality of Switch Bypass Monitor (SBM) 3.2 Use of SBM for Differentiation between Short Circuit to VS and Open Load If a short circuit to VS should be distinguished from an open load (e.g. broken bulb) an external output pull down resistor is required. The following figure shows the circuit with the additional output pull down resistor ROUT_pd: VS OUT ROUT_pd Figure 2 Load External Circuit for Open Load Detection in OFF state With the following formula the output pull down resistor ROUT_pd can be calculated to ensure during open load condition that device and system leakage currents do not cause the bit DCR.SBM to transition to a logic 0. ROUT _ pd < VS − VDS ( SB ), max I L ( OFF ), max + I SystemLeak age (5) Taking VS = 9 V, VDS(SB),max = 4.5 V, IL(OFF),max = 50 µA and neglecting system leakages for the moment, the resulting ROUT_pd should be smaller than 90 kΩ. The following figure shows the flow chart for the software strategy to distinguish between an Open Load and a short circuit to VS failure: Application Note 6 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Functionality of Switch Bypass Monitor (SBM) Legend: Process Switch MUX to active channel n Decision Measure sense voltage VIS Yes Switch OFF channel Store data No VIS < VIS(nom,min) Yes Store Read DCR.SBM Yes Display Store VIS No V IS > VIS(nom,max) ERR_MUX Switch MUX to next channel No DCR.SBM = 1 Yes SC to VS Over Load No ERR_MUX = n Channel n latched OFF (nretry reached) Yes No VIS < VIS( worstcase ) Under Load Open Load Figure 3 Decision flow chart to detect a Short Circuit to VS, a Channel Latch OFF (nretry reached) or an Open Load In the figure above a the differentiation between open load and a too low load current can be done by the implementation of a VIS threshold voltage as described in the Chapter 3.1 Application Note 7 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Functionality of Switch Bypass Monitor (SBM) 3.3 Detection and Reaction strategies The software procedures shown in Chapter 3.1 and Chapter 3.2 can be used for “single event detection”, meaning that each procedure execution will determined whether there is an Open Load, a Short Circuit to VS, or a channel latched OFF (which would be a clear indication of Short Circuit to Ground) at the time of execution. In Automotive enviroment such failure conditions can be also intermittent. In such case a “single event detection” strategy represents a too high risk for the application. For this reason OEMs usually implement a “multiple event detection” strategy. Some possible examples are: • • • • “n” events detected in a row (this is the simplest approach - n = 3 or 5 for loads where a fast detection is preferable to wrong detectiona) – this is the simplest approach – n = 3 or 5 for loads where a fast detection is preferable to a wrong detection (Turning lights, Stop lights) – n = 10 or more if the loads are less critical “n” events detected out of “m” load activation cycles (where n < m) “n” events within a given timeframe (for instance, the time between two ingnition key activations) “n” events detected in a row, with increased time delay between load activation attempts While it is possible to detect an Open Load or a Short Circuit to VS when the load is OFF, the detection of a Short Circuit to Ground requires at least one activation (in other words, an ON phase). In modern automotive applications hardly this represents a problem. In general many lamps or LED are operated in PWM, with frequency range from 80 Hz to 200 Hz. In this way each load can have a diagnosis in ON and one in OFF within a short (12 ms for 80 Hz) timeframe. When the multiple event detection condition is reached, the microcontroller reacts accordingly. Both Detection and Reaction strategies can be different from OEM to OEM, although some elements are common because fixed by law. For example a malfunction (Open Load, Short Circuit to Ground, Short Circuit to VS) detected at one lamp or LED used for as Turning light forces a double intermittance frequency on the others Turning lights. The general response to a detection (valid for any malfunction) can include: • • • load deactivation blinking at double frequency for the other loads with the same function (Turning lights) warning lamp on the dashboard or a warning message displayed on the board computer (optional, normally reserved to premium cars) A simplified general strategy for Detection and Reaction can be the following: 1. Perform diagnostic procedure on every PWM cycles – In case of many loads with different PWM frequency, the slowest one (the one with the lowest frequency) should be taken as reference – Diagnostic in ON state and in OFF state should be done at least once for every PWM cycle of the reference load 2. Perform a “multiple event detection” – Turning lights: 3 events in a row, or 4 events in 6 diagnosis cycles – Stop lights: 5 events in a row, or 7 events in 10 diagnosis cycles – Other lights (Head Lamp, Tail Lamp, etc.): 10 events in a row, where the first activation is driven by the user and the other 9 are controlled by the microcontroller to attempt an error recovery 3. Adapt the reaction to the load type – Turning lights: load deactivated - other Turning lights blinking at double frequency – Stop lights: load deactivated – Other lights (Head Lamp, Tail Lamp, etc.): load deactivated Application Note 8 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Conclusion 4 Conclusion By the use of the Switch Bypass Monitor it is possible to distinguish between the operation modes described in Chapter 2. Therefore, a sophisticated software strategy is required. Summary: • • Without any external hardware it is possible to distinguish between short circuit to VS, channel latched OFF and an Under Load. A complete differentiation between short circuit to VS and Open Load is not possible. By using an external output pull down resistor it is possible to distinguish between short circuit to VS, Open Load, channel latched OFF and Under Load conditions. 5 Additional Information The following table shows the corresponding SPI commands needed for the flow charts showed in Figure 1 and Figure 3. Further information about SPOCTM+ 12V SPI protocol are available in product datasheets. Table 4 SPI commands for flow chart “processes” Requested Operation Frame sent to SPOC+ (SI pin) Frame received from SPOC+ (SO pin) with the next command Switch MUX to active channel “n” 11110aaaB 0aaaaaaaB where “aaaB” = n - 1 in binary (Standard Diagnosis) example: when MUX must be set to channel 3 the corresponding command is 11110010B (3 - 1 = 2 → 010 in binary) Switch OFF channel “n” 0aaaaaaaB 10aaaaaaB where “aaaaaaB” is the content that (Standard Diagnosis) needs to be written in the Output Configuration Register OUT. The number of bits that can be written depends on the SPOCTM+ 12V product used. Read DCR.SBM bit Application Note 01110000B 1111abbbB where: “aB” = DCR.SBM status “bbbB” = DCR.MUX status 9 Rev. 1.0, 2013-09-25 SPOCTM+ 12V Short Circuit to VS and Open Load Detection Revision History 6 Revision History Revision Date Changes Rev. 1.0 2013-09-25 Application Note released Application Note 10 Rev. 1.0, 2013-09-25 Edition 2013-09-25 Published by Infineon Technologies AG 81726 Munich, Germany © 2013 Infineon Technologies AG All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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