AN4834, Output Current Sensing - Application Note

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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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11
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Document Number: AN4834
Rev. 3.0
5/2015
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