Freescale Semiconductor Application Note Document Number: AN5066 Rev. 1.0, 1/2015 Repetitive Short-circuit Performances Featuring the MC12XS6 IC's family 1 Introduction This application note relates to the robustness of devices of the eXtreme Switch MC12XS6 device family in cases of various repetitive short-circuit conditions. The MC12XS6 family is the latest achievement in term of low-voltage lighting applications. It is an evolution of the successful generation of MC12XS3 eXtreme Switches. This family is composed of nine different devices. Those dual, triple, quad, and penta outputs devices are footprint and software compatible, with a wide panel of low RDS(on) MOSFETs fitting the various types of automotive and industrial bulbs. Programming, control, and diagnostics are accomplished using a 16-bit SPI interface, which provides a large panel of configurations, analog and digital information related to the device in its application, and a full set of protection features to ensure its safety. All information provided by this SMARTMOS device through the SPI gives the MCU all the key information to reflect device and output status. This device also provides a wide flexibility of configurations in addition to highly sophisticated fault and failure mode handling. For feature information, refer to the individual device data sheets. © Freescale Semiconductor, Inc., 2015. All rights reserved. Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Short-circuit Protection Strategy. . . . . . . . . . . . . . . 2 3 Repetitive Short-circuit Test Setup . . . . . . . . . . . . . 4 4 Repetitive Short-circuit Test Results . . . . . . . . . . . 6 5 Engineering Evaluations . . . . . . . . . . . . . . . . . . . . . 7 6 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Short-circuit Protection Strategy 2 Short-circuit Protection Strategy The MC12XS6 devices include up to five self-protected high-side switches, with its extended protection and diagnostics, to detect bulb outage and short-circuit fault conditions. Additionally, this device incorporates a pulse width modulation control module, to improve lamp lifetime with bulb power regulation at no less than 25 Hz, and address the dimming application (daytime running light). The MC12XS6 family proposes different load protection features: • latched overcurrent protection, • severe short-circuit protection. • overcurrent in the On state Those protections are preferred to conventional current limitations, to minimize the thermal overstress within the device in cases of overload conditions. The delta (T) is drastically reduced to a value which does not affect the device's reliability. 2.1 Transient Overcurrent Protection MC12XS6 includes a transient overcurrent protection at each Turn On command. This profile, represented in Figure 1, is configurable through the SPI: • OCHI1 can be decreased by 15% or 50%, depending on the dynamic output voltage at Turn On or ambient temperature • OCHI1…3 can be adjusted from 37 ms (Short OCHI feature) to 130 ms (NO HID feature) • OCLO threshold has three selectable values and a range from 2.0 A to 22 A over the family • OCHI1/2/3 profile could also be disabled during turn On, in case of a resistive load (NO OCHI feature) • MC12XS6 offers the possibility to start another transient overcurrent profile in the On state when the output current exceeds OCLO (OCHI OD feature) Figure 1. Multi-step Transient Overcurrent Protection 2.2 Severe Short-circuit Protection In addition to latched overcurrent protection, a severe short-circuit detection is available during lamp switching to immediately turn off the output in cases of an extremely low short-circuit event. This feature lowers the junction temperature in this extreme condition where the high-side MOSFET is not yet in the RDS(on) state. 2.3 Short-circuit in the On State The configurable OCLO threshold is triggered once the OCHI1/2/3 profile is passed and available for as long as the output stays on. It acts as a fuse with configurable values and protects the output once the transient trip is gone. However, the device could allow transient events while in the On state during user demands, with the OCHI OD feature. AN5066 Application Note Rev. 1.0 1/2015 2 Freescale Semiconductor Short-circuit Protection Strategy 2.4 Digital Diagnostics For each of those previous listed undesirable events, the type of fault can be distinguished through a specific SPI register, dedicated per output. Table 1. Output Channel Status Register SO Address # Ch 1…5 status 2…0 SO Data D15 D14 D13 D12 D11 D10 D9 D8 D7 0 x x x Fm DSF OVLF OLF res D6 D5 D4 D3 D2 D1 D0 OTSx OTWx OC2x OC1x OC0x OLONx OLOFFx The SO output register provides a detailed diagnostic for each channel where Open Load or Thermal diagnostics are listed, alongside the type of overcurrent event (bits OC[0…2]x). Figure 2 shows the various type of event that are reported into the channel status SPI register. #2~#6 OC2x OC1x OC0x over current status 0 0 0 no overcurrent 0 0 1 OC HI1 0 1 0 OC HI2 0 1 1 OC HI3 1 0 0 OC LO 1 0 1 OC HIOD 1 1 0 SSC 1 1 1 not used Figure 2. Overcurrent Status Flags AN5066 Application Note Rev. 1.0 1/2015 Freescale Semiconductor 3 Repetitive Short-circuit Test Setup 3 Repetitive Short-circuit Test Setup The repetitive short-circuit tests were performed in accordance with Chapter 12 of AEC-Q100 specification, published by the Automotive Electronics Council (last revision September14, 2006). The goal is to force the device to switch “On” and “Off” cyclically in a short-circuit condition to accelerate silicon device fatigue. In addition, Freescale performed its own tests adapted to the device's protections, to fulfill the different use cases in an application. 3.1 Short-circuit Conditions Some test cases are defined in the AEC specification: • Hot Repetitive Short-circuit Test: an infinite “on” command where the temperature does NOT return to operating temperature (TAMB) between each pulse • Cold Repetitive Short-circuit Test - Short Pulse: a repetitive turn-on command of 10 ms periods where the temperature returns to operating temperature (TAMB) between each pulse • Cold Repetitive Short-circuit Test - Long Pulse: a repetitive turn-on command of 300 ms periods where the temperature returns to operating temperature (TAMB) between each pulse The short-circuit case applied to the Smart Power Switch is dependent of its failure handling during short-circuit events. Figure 3. AECQ100-12 Decision Tree Based on the decision tree, Freescale performs its robustness assessment in cold repetitive short-circuit short pulse conditions. Figure 4 illustrates the typical hardware used for the assessment. Figure 4. AECQ100-12 Short-circuit Test Setup AN5066 Application Note Rev. 1.0 1/2015 4 Freescale Semiconductor Repetitive Short-circuit Test Setup Tests applied for the MC12XS6 devices were based on specific short-circuit conditions, activating each overload protection feature, as described in Table 2. and Figure 5. Table 2. Short-circuit Test Types Test # (2) Description 1 Terminal short-circuit of 20 m (RSHORT) AECQ100-12 and Freescale Test 2 Load short-circuit of 50 m or 100 m (RSHORT) (1) AECQ100-12 and Freescale Test 3 Overload condition exceeding the nominal current Freescale Test 4 Overcurrent in the On-state (applied after Transient overcurrent profile) Freescale Test Notes 1.RSHORT is choosen depending on ISHORT (RSHORT = 50 m if ISHORT > 100 A) 2.These test numbers refers to those identified in Figure 5. Figure 5. Repetitive Short-circuit Tests Modes 3.2 Hardware environment for short-circuit tests According to the conditions outlined in the previous section, the available hardware fulfills the following requirements: • Fixed input and output inductance value • Variable input and output resistance values • Configurable ambient temperature • High sample quantity capability • Continuous individual SPI monitoring to record the exact number of cycles to failure Devices are mounted on 4 layer PCBs, with layout and construction reflecting the application conditions. Each PCB is inserted into sockets that are on a common Burn-in-board (10 PCBs per Burn-in-board). The line impedance represents the wire harness put on each Input/output of each PCB. Burn-in-boards are loaded in a thermally controlled oven with outside connections for power and logic. Permanent monitoring performed by the supervision can digitally trace the different failures reported by each device. AN5066 Application Note Rev. 1.0 1/2015 Freescale Semiconductor 5 Repetitive Short-circuit Test Results 4 Repetitive Short-circuit Test Results Table 3. presents the summary of repetitive test results for all devices from the MC12XS6 family in AECQ100-12 test conditions. Tests have been performed for load short-circuit condition, and for each device: Table 3. AECQ100-12 Reliability Test Results at TAMB = 85 °C and Voltage = 14 V Short-circuit Case (3) Supply Line Terminal short-circuit on 7.0 m, 8.0 m, and 10 m outputs (test 1) Load Line AECQ100-12 Grade A 5.0 H/20 m Terminal short-circuit on 17 m, 21 m, 25 m, and 40 moutputs (test 1) A 5.0 H/10 m Load short-circuit on 7.0 m, 8.0 m, and 10 m outputs (test 2) 5.0 H/100 m D Load short-circuit on 17 m, 21 m, 25 m, and40 m outputs (test 2) 5.0 H/50 m D Notes 3.These test numbers refers to those identified in Figure 5. Table 4. shows the summary of repetitive short-circuit tests in custom conditions. Those results are extracted from performances of three devices over the family: MC07XS6517, MC17XS6500, and MC17XS6400, and done on all output types. Tests were voluntary stopped at 500 k cycles. Table 4. Freescale Repetitive Short-circuit Test Results at TAMB = 70 °C Battery Voltage Short-circuit case Supply Line 0.3 m/2.5 mm2 Turn On into short-circuit condition (tests 1 and 2) 16 V 5.0 m/2.5 mm2 0.3 m/2.5 mm2 Short-circuit in On state (test 4) 14 V 5.0 m/2.5 mm2 On state overload 95% of OCHI1/2/3 level (test 3) 16 V 0.3 m/6.0 mm2 Load Line Fault Triggered Output Cycle Without Failure 5.0 m/1.0 mm2 OCHI1 (test 2) (4) > 500 k SSC (test 1) (4) > 500 k Undervoltage > 500 k 0.3 m/1.0 mm2 5.0 m/1.0 mm2 0.3 m/1.0 mm2 > 500 k OCLO > 500 k > 500 k 0.3 m/6.0 mm2 OCHI1/2/3 > 1.0 M Notes 4.These test numbers refers to those identified in Figure 5. AN5066 Application Note Rev. 1.0 1/2015 6 Freescale Semiconductor Engineering Evaluations 5 Engineering Evaluations The device's level of robustness is a function of ambient temperature. With the default device's configuration, the number of cycles to failure decreases above 50 °C. Several features embedded in the device help maximize the device robustness in different application cases. • Feature OCHI-15%: once the embedded thermal sensor detects an ambient temperature above 63 °C, the robustness of the device is improved, thanks to a lower power dissipation during short-circuit conditions • Overtemperature shutdown (OTS): With a high ambient temperature (> 110 °C) the device may shutdown with the OTS feature, at a lower current peak, resulting in a lower power dissipation during a short-circuit • NO OCHI: Depending on the application and ambient temperature, which eliminates the lamp inrush, the OCHI window can be disabled during turn on, significantly minimizing the thermal increase during a short-circuit • When a PWM is applied to the lamps by the SPI, the OCHI window is disabled for each commutation except the 1st one Based on these statements and engineering studies done internally, Figure 6 shows the derating results over the ambient temperature in the AECQ100-12 conditions. Figure 6. AECQ100-12 Results Over Ambient Temperature Grades mentioned on Table 3. and Figure 6 pertain to Table 5. which are extractions from the AECQ100-12 reliability standard. Table 5. AECQ100-12 Reliability Standards Grade # Cycles Lots/Samples per Lot # Fails A > 1,000,000 3/10 0 B > 300,000 — 1,000,000 3/10 0 C > 100,000 — 300,000 3/10 0 D > 30,000 — 100,000 3/10 0 E > 10,000 — 30,000 3/10 0 F > 3000 — 10,000 3/10 0 G > 1000 — 3000 3/10 0 H 300 — 1000 3/10 0 O < 300 3/10 0 AN5066 Application Note Rev. 1.0 1/2015 Freescale Semiconductor 7 References 6 References Document Number and Description MC12XS6D3 MC12XS6D3 URL http://cache.freescale.com/files/analog/doc/data_sheet/MC12XS6D1.pdf Data Sheet MC12XS6D4 http://cache.freescale.com/files/analog/doc/data_sheet/MC12XS6D3.pdf http://cache.freescale.com/files/analog/doc/data_sheet/MC12XS6D4.pdf Freescale.com Support Pages MC12XS6 Product Summary Page Power Management Home Page Analog Home Page URL http://www.freescale.com/webapp/sps/site/prod_summary.jsp http://www.freescale.com/webapp/sps/site/homepage.jsp?code=POWERMGTHOME http://www.freescale.com/analog AN5066 Application Note Rev. 1.0 1/2015 8 Freescale Semiconductor Revision History 7 Revision History Revision Date 1.0 1/2015 Description of Changes Initial release AN5066 Application Note Rev. 1.0 1/2015 Freescale Semiconductor 9 How to Reach Us: Information in this document is provided solely to enable system and software implementers to use Freescale products. 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