Freescale Semiconductor, Inc. Application Note Document Number: AN4834 Rev. 3.0, 5/2015 Output Current Sensing For the MC12XS6 eXtreme Switch Device Family 1 Introduction This application note describes current sense performances for SMARTMOS eXtreme switch devices belonging to the MC12XS6 family. The application note covers • the enhanced current sense mode dedicated to low current loads, such as light emitting diodes (LED) • current sense accuracy • the practical implementation of a calibration procedure to get optimized results This document does not address errors linked to MCU and the external resistor connected to the CSNS pin. © Freescale Semiconductor, Inc., 2015. All rights reserved. Contents Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Chapter 3 Selectable Current Sensing Overview . . . . . . . . . . . . 3 Chapter 4 Device Performance Without Calibration . . . . . . . . . . 5 Chapter 5 Device Performance with Calibration . . . . . . . . . . . . . 7 Chapter 6 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Chapter 7 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Scope 2 Scope The eXtreme switch MC12XS6 family is the latest achievement in automotive lighting drivers. It consists of a scalable family of devices compatible in software, MCU interface, and footprint. This product family is designed for low-voltage automotive and industrial lighting applications, and is composed of nine devices with various RDS(on) values and number of outputs to best fit various load and applications. All devices of this family are footprint and software compatible. Table 1. MC12XS6 Family Part Number Type MC07XS6517BEK Penta MC17XS6500BEK Penta MC17XS6400EK Datasheet OUT1 OUT2 OUT3 OUT4 OUT5 17 m 17 m 7.0 m 7.0 m 7.0 m 17 m 17 m 17 m 17 m 17 m Quad 17 m 17 m 17 m 17 m NC MC25XS6300EK Triple 25 m 25 m 25 m NC NC MC10XS6325EK Triple 25 m NC 10 m 10 m NC MC12XS6D1 MC12XS6D2 MC10XS6200EK Dual NC NC 10 m 10 m NC MC10XS6225EK Dual 25 m NC 10 m NC NC MC40XS6500EK Penta MC12XS6D3 40 m 40 m 40 m 40 m 40 m MC08XS6421EK Quad MC12XS6D4 21 m 21 m 8.0 m 8.0 m NC This application note refers to the enhanced analog feedback provided by the device with its CSNS pin. This output pin of the IC is dedicated for battery voltage, IC's temperature or current sensing. The family of eXtreme switches include an Advanced Current Sensing mode (ACM) giving an optimized accuracy of the output current from each channel. In this mode, the error amplifier offset contribution to the CSNS error can be eliminated from the measurement result by averaging each of two sequential current sense measurements. VBAT VBAT VBAT VCC 5.0 V Regulator GND VCC Main MCU GND SO CSB SCLK SI RSTB CLK A/D1 TRG1 PORT PORT PORT PORT PORT A/D2 VBAT VCC SI CP CSB OUT1 SCLK SO OUT2 RSTB CLK OUT3 CSNS SYNCB OUT4 LIMP IN1 OUT5 IN2 IN3 IN4 GND OUT6 VBAT OUT Smart Power CSNS GND IN Figure 1. Typical Application Diagram AN4834 Output Current Sensing Rev. 3.0 5/2015 2 Freescale Semiconductor, Inc. Selectable Current Sensing Overview 3 Selectable Current Sensing Overview 3.1 Current Sense Definition The CSNS output pin of the device provides ratio metric feedback of the output current of each channel (multiplexed by the SPI). The maximum current reported by the CSNS pin (1.0 mA) corresponds to the maximum current allowed on the corresponding channel. This maximum current varies along the RDS(on) type and the SPI configuration (full scale range). 1.0 mA ICSNS/IOUT = 1.0 mA/(100% FSR) typ. Note: FSR value depends on the SPI setting 0 mA Figure 2. Current Sense Interpretation The current sensing can be adjusted according to the intended lamp wattage and operation mode. An overcurrent active low signal can be configured for each channel corresponding to the full scale range (FSR) current of the affected channel. There are two bits available on the SPI register to set the correct FSR related to selected application. A default FSR value (OCLO bit = ACM bit = 0) can be divided by two or four, depending on this configuration. Figure 3 shows FSR (right side) and accuracy (left side) for all RDS(on) values composed by the family vs. the SPI register configuration: overcurrent low (OCLO) and Advanced Current Sensing mode (ACM). Current Sense (OCLO = 0, ACM = 1) Reduced Precision Analog Current Sense Current Sense (OCLO = 1, ACM = 1) Reduced Precision Current Sense (OCLO = 0, ACM = 0) Current Sense (OCLO = 1, ACM = 0) ILOAD[mA] 7.0 & 8.0 m channel: 55 110 220 5500 11000 22000 10 m channel: 45 90 180 4500 9000 18000 27.5 55 110 2750 5500 11000 24 48 96 2400 4800 9600 19.5 39 78 1950 3900 7800 17 & 21 m channel: 25 m channel: 40 m channel: 1% FSR values vs. selected mode 100% FSR values vs.selected mode Figure 3. Current Sense Performances vs. SPI Register Configuration As an example, if the 7.0 m output is configured with OCLO = 1 and ACM = 0, then FSR = 11 A. With an output current of 5.5 A, the CSNS pin provides 500 A. AN4834 Output Current Sensing Rev. 3.0 5/2015 Freescale Semiconductor, Inc. 3 Selectable Current Sensing Overview 3.2 Current Sense Performances at Low Current The current sense is unique in the market for its high reliability to diagnose either low or high current with an enhanced accuracy. Table 2 shows the minimum current sense reporting accuracy for both extreme RDS(on) values along the family: MC07XS6517B for 7.0 m and 17 m, and MC40XS6500 for 40 m channel performance. Values displayed are based on the statistical analysis of three different lots for each device with 3-Sigma (these are not the limits from the specification). It shows the default accuracy (No Calibration) as well as with 1 or 2 points calibration. Extracted values come from the configuration OCLO bit = 1 and ACM bit = 0. Table 2. Minimum Current Sense Accuracy in OCLO = 1 (no ACM) for 7.0, 17, and 40 m Channels 07XS6517B (OCLO = 1 / ACM = 0) - FSR = 5.5/11A 40XS6500 (OCLO = 1 / ACM = 0) - FSR = 3.9A Min/Max precision % FSR Absolute Current Min/Max precision No calibration 1pt offset calibration 2pts calibration Min Max Min Max Min Max Absolute Current % FSR No calibration 1pt offset calibration 2pts calibration Min Max Min Max Min Max OUT1 (17 m) 1% 55.0 mA -42% 59% -40% 50% -40% 50% OUT1 (40 m) 1% 39.0 mA -30% 36% -28% 31% -28% 31% OUT2 (17 m) 1% 55.0 mA -46% 49% -44% 39% -43% 39% OUT2 (40 m) 1% 39.0 mA -33% 32% -29% 26% -28% 25% OUT3 (7.0 m) 1% 110.0 mA -62% 66% -57% 56% -57% 56% OUT3 (40 m) 1% 39.0 mA -37% 32% -34% 23% -34% 23% OUT4 (7.0 m) 1% 110.0 mA -64% 61% -59% 50% -59% 50% OUT4 (40 m) 1% 39.0 mA -41% 32% -38% 23% -38% 22% OUT5 (7.0 m) 1% 110.0 mA -68% 56% -61% 50% -61% 49% OUT5 (40 m) 1% 39.0 mA -38% 40% -31% 22% -32% 23% ACM mode helps to significantly improve the accuracy at low output current as shown in Table 3. Table 3. Minimum Current Sense Accuracy in OCLO = 1 and ACM Mode = 1 for 7.0, 17, and 40m Channels 07XS6517B (OCLO = 1 / ACM = 1) - FSR = 2.75/5.5A 40XS6500 (OCLO = 1 / ACM = 1) - FSR = 1.95A Min/Max precision % FSR Absolute Current Min/Max precision No calibration 1pt offset calibration 2pts calibration Min Max Min Max Min Max % FSR Absolute Current No calibration 1pt offset calibration 2pts calibration Min Max Min Max Min Max OUT1 (17 m) 1% 27.5 mA -22% 21% -12% 13% -11% 12% OUT1 (40 m) 1% 19.5 mA -20% 11% -9% 9% -8% 8% OUT2 (17 m) 1% 27.5 mA -20% 22% -11% 13% -10% 13% OUT2 (40 m) 1% 19.5 mA -19% 13% -7% 9% -6% 8% OUT3 (7.0 m) 1% 55.0 mA -36% 30% -25% 17% -25% 17% OUT3 (40 m) 1% 19.5 mA -15% 16% -9% 9% -8% 9% OUT4 (7.0 m) 1% 55.0 mA -34% 30% -25% 17% -24% 17% OUT4 (40 m) 1% 19.5 mA -17% 19% -11% 10% -10% 9% OUT5 (7.0 m) 1% 55.0 mA -44% 24% -27% 18% -26% 18% OUT5 (40 m) 1% 19.5 mA -14% 21% -9% 10% -8% 10% The following pages show the current sense precision for the power output channels 7.0, 10, 17, 25, and 40 m of the 07XS6517B, 17XS6500B, 17XS6400, 10XS6225, 10XS6200, 10XS6325, 25XS6300, and 40XS6500(1). Accuracy is displayed for the worst case output of each RDS(on) value. All graphs present the data with: X-axis = Full Scale Range/Y-axis = min/max% error on the value read on the CSNS pin. Notes 1. Device 08XS6421 shares the same performances as the 07XS6517B and is not shown on the following pages. The data presented are valid within the temperature range -40 °C < TAMB < 125 °C and voltage range 9.0 V < Voltage < 18 V The following "trumpet curves" represent the following configurations: Current sense precision without calibration: 1. Devices performances in non-ACM configuration and OCLO = 1 2. Devices performances in ACM configuration and OCLO = 1 Current sense precision with calibration: 1. Devices performances in ACM and OCLO = 1 - 1 point Offset calibration 2. Devices performances in ACM and OCLO = 1 - 2 points Offset calibration AN4834 Output Current Sensing Rev. 3.0 5/2015 4 Freescale Semiconductor, Inc. Device Performance Without Calibration 4 Device Performance Without Calibration 4.1 Device Performances in Non-ACM Configuration and OCLO = 1 MC07XS6517 Output5 7.0 m: OCLO = 1/ACM = 0 (FSR = 11 A) 70% 70% 1% FSR (Iout= 110 mA) 50% 50% 30% 2% 5% 10% -10% 0 30% 10 % 10 100% FSR (Iout = 11 A) 25 % 20 30 40 50 60 70 80 90 100 % error % error MC10XS6225 Output3 10 m: OCLO = 1/ACM = 0 (FSR = 9.0 A) 10% -10% 0 -30% -30% -50% -50% -70% 10 20 40 50 -70% % FSR 60 70 80 90 100 70 80 90 100 % FSR MC10XS6225 Output1 25 m: OCLO = 1/ACM = 0 (FSR = 4.8 A) MC17XS6400 Output4 17 m: OCLO = 1/ACM = 0 (FSR = 5.5 A) 60% 30 60% 50% 40% 40% 30% 0% 0 10 20 30 40 50 60 70 80 90 100 20% % error % error 20% 10% -20% 0% -10% -40% -60% 0 10 20 30 40 50 60 -20% -30% % FSR % FSR MC40XS6500 Output5 40 m: OCLO = 1/ACM = 0 (FSR =3.9 3.8 A A) 40% % error 20% 0% 0 10 20 30 40 50 60 70 80 90 100 -20% -40% % FSR Figure 4. Devices in Configuration OCLO Bit = 1; ACM Bit = 0 AN4834 Output Current Sensing Rev. 3.0 5/2015 Freescale Semiconductor, Inc. 5 Device Performance Without Calibration 4.2 Device Performances in ACM Configuration and OCLO = 1 MC07XS6517B Output5 7.0 m: OCLO = 1/ACM = 1 (FSR = 5.5 A) 30% MC10XS6325 Output3 10 m: OCLO = 1/ACM = 1 (FSR = 4.5 A) 30% 20% 10% 0 10 20 30 40 50 60 70 80 90 100 -10% % error % error 10% 0% 0 10 20 30 40 50 60 70 80 90 100 80 90 100 -10% -20% -30% -30% -50% -40% % FSR MC17XS6500B Output5 17 m: OCLO = 1/ACM = 1 (FSR = 2.75 A) 40% % FSR MC10XS6325 Output1 25 m: OCLO = 1/ACM = 1 (FSR = 2.4 A) 20% 30% 10% 10% Axis Title % error 20% 0% 0 10 20 30 40 50 60 70 80 90 100 0% 0 10 20 30 40 50 60 70 -10% -10% -20% -20% -30% -30% % FSR % FSR MC40XS6500 Output3 40 m: OCLO = 1/ACM = 1 (FSR = 1.95 A) 20% % error 10% 0% 0 10 20 30 40 50 60 70 80 90 100 -10% -20% % FSR Figure 5. Devices in Configuration OCLO Bit = 1; ACM bit = 1 AN4834 Output Current Sensing Rev. 3.0 5/2015 6 Freescale Semiconductor, Inc. Device Performance with Calibration 5 Device Performance with Calibration The accuracy of the current sensing depends on the following contributors: 1. Device-to-device variation due to manufacturing 2. Output current vs. selected full scale range 3. Ambient temperature range -40 °C to 125 °C 4. Battery voltage range 9.0 V to 18 V With a calibration strategy, the precision of current sensing can be improved significantly. It helps to remove the device-to-device effect or the offset error at low output current. Calibration is the process which determines the exact gain and offset values for specific parts. The onboard microcontroller calculates IOUT according to the formula: IOUT = (ICSNS*GAIN) + OFFSET ICSNS ICSNS ICSNS/IOUT = 1.0 mA/(100% FSR) typ. 1.0 mA 1mA IMIN( CSNS) IMIN(CSNS) 100% FSR IIOUT OUT 100% FSR Figure 6. Output Current Sensing Notes 2. FSR value depends on the SPI setting, as described in Section 3,"Selectable Current Sensing Overview". Two different calibration strategies are proposed: • One calibration point - Offset calibration — TAMB = 25 °C/VBAT = 14 V — IOUT = 2.0% FSR • Two calibration points (ACC ICSNS 2 CAL) - Offset and Gain calibration — TAMB = 25 °C/VBAT = 14 V — IOUT = 2.0% FSR (Offset calibration) and IOUT = 50% FSR (Gain calibration) These calibration procedures help to improve current sense precision for a voltage range between 9.0 V and 18 V, and the ambient temperature range -40 °C < TA < 125 °C. The following pages show the current sense accuracy with 1 point offset or 2 points gain + offset calibration at 14 V. Pictures are shown for the worst case output of each RDS(on) in ACM mode. For 1 point Gain calibration performances, refer to the specification in Section 6,"References". AN4834 Output Current Sensing Rev. 3.0 5/2015 Freescale Semiconductor, Inc. 7 Device Performance with Calibration 5.1 Device Performances in ACM and OCLO = 1 with 1 Point Offset Calibration MC07XS6517B Output5 7.0 m: OCLO = ACM = 1 (FSR = 5.5 A) Calibration : 1 pt offset at 110 mA 20% MC10XS6225 Output3 10 m: OCLO = 1/ACM = 1 (FSR = 4.5 A) Calibration : 1 pt offset at 90 mA 30% 20% 10% 0 10 20 30 40 50 60 70 80 90 100 -10% % error % error 10% 0% 0% 0 10 20 30 40 50 60 70 80 90 80 90 100 -10% -20% -20% -30% -30% % FSR MC17XS6500B Output5 17 m: OCLO = ACM = 1 (FSR = 2.75 A) Calibration : 1 pt offset at 55 mA 20% 10% 10% 5% 0% 0 10 20 30 40 50 60 70 MC10XS6225 Output1 25 m: OCLO = 1/ACM = 1 (FSR = 2.4 A) Calibration : 1 pt offset at 48 mA 15% 80 90 100 % error % error 30% % FSR 0% 0 -10% -5% -20% -10% -30% 10 20 30 40 -15% 50 60 70 100 % FSR % FSR MC40XS6500 Output5 40 m: OCLO = ACM = 1 (FSR = 1.95 A) Calibration : 1 pt offset at 38 mA 10% % error 5% 0% 0 10 20 30 40 50 60 70 80 90 100 -5% -10% % FSR Figure 7. Devices in Configuration OCLO Bit = 1; ACM bit = 1; Calibration = 1 point offset (2%FSR)/Voltage = 14 V AN4834 Output Current Sensing Rev. 3.0 5/2015 8 Freescale Semiconductor, Inc. Device Performance with Calibration 5.2 Devices Performances in ACM and OCLO = 1 with 2 Points Offset Calibration MC07XS6517B Output5 7.0 m: OCLO = ACM = 1 (FSR = 5.5 A) Calibration : 1 pt offset at 110 mA/1 pt Gain at 2.75 A 20% 25% 15% 10% 0% 0 10 20 30 40 50 60 70 80 90 100 -10% 5% % error % error MC10XS6225 Output3 10 m OCLO = ACM = 1 (FSR = 4.5 A) Calibration : 1 pt offset at 90 mA/1 pt Gain at 2.25 A -20% -5% 0 10 20 30 40 50 60 70 80 90 100 -15% -30% -25% % FSR % FSR MC17XS6500B Output5 17 m: OCLO = ACM = 1 (FSR = 2.75 A) Calibration : 1 pt offset at 55 mA/1 pt Gain at 1.375 A 30% MC25XS6300 Output3 25 m OCLO = ACM = 1 (FSR = 2.4 A) Calibration : 1 pt offset at 48 mA/1 pt Gain at 1.2 A 20% 15% 20% 10% 5% 0% 0 10 20 30 40 50 60 70 80 90 100 % error % error 10% 0% 0 10 20 30 40 50 60 70 80 90 100 -5% -10% -10% -20% -15% -30% -20% % FSR % FSR MC40XS6500 Output3 40 m: OCLO = ACM = 1 (FSR = 1.95 A) Calibration : 1 pt offset at 38 mA/1 pt Gain at 975 mA 10% % error 5% 0% 0 10 20 30 40 50 60 70 80 90 100 -5% -10% % FSR Figure 8. Devices in Configuration OCLO Bit = 1; ACM bit = 1; Calibration = 1 point offset (2%FSR)/1 point Gain (50%FSR)/Voltage = 14 V AN4834 Output Current Sensing Rev. 3.0 5/2015 Freescale Semiconductor, Inc. 9 References 6 References Following are URLs where you can obtain information on related Freescale products and application solutions: Document Number Description URL MC12XS6 Product Summary Page http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC12XS6 Analog Home Page Home Page http://www.freescale.com/analog AN4834 Output Current Sensing Rev. 3.0 5/2015 Freescale Semiconductor, Inc. 10 Revision History 7 Revision History Revision Date 1.0 2/2014 2.0 3.0 5/2014 5/2015 Description • Initial release • • • • Version pass 1p4 added for this AN Current Sense Performances vs. SPI Register Configuration figure updated Minimum Current Sense Reporting in ACM Mode and OCLO = 1 figure added Chapters 4 & 5 reworked. Adapted format to display trumpet curves for all channels in OCLO = 1, ACM or non-ACM, without calibration (Device Performance Without Calibration), and 1 or 2 points with calibration (Devices Performances in ACM and OCLO = 1 with 2 Points Offset Calibration) • • • • Scope completed with additional explanation on current sense Results adapted for version B of the 07XS6517 and 17XS6500 Curves removed to simplify the document Performances of all 12XS6 devices integrated in the document AN4834 Output Current Sensing Rev. 3.0 5/2015 Freescale Semiconductor, Inc. 11 How to Reach Us: Information in this document is provided solely to enable system and software implementers to use Freescale Home Page: freescale.com products. There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated Web Support: freescale.com/support Freescale reserves the right to make changes without further notice to any products herein. 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Freescale and the Freescale logo are trademarks of Freescale Semiconductor, Inc., Reg. U.S. Pat. & Tm. Off. SMARTMOS is a trademark of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © 2015 Freescale Semiconductor, Inc. Document Number: AN4834 Rev. 3.0 5/2015