AD8418 [ADI]

Bidirectional, Zero Drift, Current Sense Amplifier; 双向,零漂移,电流检测放大器
AD8418
型号: AD8418
厂家: ADI    ADI
描述:

Bidirectional, Zero Drift, Current Sense Amplifier
双向,零漂移,电流检测放大器

放大器
文件: 总16页 (文件大小:300K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
Bidirectional, Zero Drift,  
Current Sense Amplifier  
AD8418  
Data Sheet  
FEATURES  
GENERAL DESCRIPTION  
Typical 0.1 µV/°C offset drift  
The AD8418 is a high voltage, high resolution current shunt  
amplifier. It features an initial gain of 20 V/V, with a maximum  
0.15% gain error over the entire temperature range. The  
buffered output voltage directly interfaces with any typical  
converter. The AD8418 offers excellent input common-mode  
rejection from −2 V to +70 V. The AD8418 performs bidirectional  
current measurements across a shunt resistor in a variety of  
automotive and industrial applications, including motor  
control, battery management, and solenoid control.  
Maximum 400 µV voltage offset over full temperature range  
2.7 V to 5.5 V power supply operating range  
Electromagnetic interference (EMI) filters Included  
High common-mode input voltage range  
−2 V to +70 V operating  
−4 V to +85 V survival  
Initial gain = 20 V/V  
Wide operating temperature range: −40°C to +125°C  
Bidirectional operation  
Available in 8-lead SOIC and 8-lead MSOP  
Common-mode rejection ratio (CMRR): 86 dB, dc to 10 kHz  
Qualified for automotive applications  
The AD8418 offers breakthrough performance throughout the  
−40°C to +125°C temperature range. It features a zero drift core,  
which leads to a typical offset drift of 0.1 µV/°C throughout the  
operating temperature range and the common-mode voltage  
range. The AD8418 is fully qualified for automotive applications  
and includes EMI filters and patented circuitry to enable output  
accuracy with pulse-width modulation (PWM) type input  
common-mode voltages. The typical input offset voltage is  
200 µV. The AD8418 is offered in 8-lead MSOP and SOIC  
packages.  
APPLICATIONS  
High-side current sensing in  
Motor controls  
Solenoid controls  
Power management  
Low-side current sensing  
Diagnostic protection  
Table 1. Related Devices  
Part No.  
AD8205  
AD8206  
AD8207  
AD8210  
Description  
Current sense amplifier, gain = 50  
Current sense amplifier, gain = 20  
High accuracy current sense amplifier, gain = 20  
High speed current sense amplifier, gain = 20  
FUNCTIONAL BLOCK DIAGRAM  
V
= –2V TO +70V  
V = 2.7V TO 5.5V  
S
CM  
70V  
V
V
1
REF  
S
V
OUT  
V
V
S
AD8418  
CM  
0V  
+IN  
–IN  
EMI  
+
FILTER  
I
SHUNT  
OUT  
G = 20  
R
SHUNT  
V /2  
S
EMI  
FILTER  
50A  
SHUNT  
–50A  
I
0V  
GND  
V
2
REF  
Figure 1.  
Rev. 0  
Document Feedback  
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other  
rightsof third parties that may result fromits use. Specifications subject to change without notice. No  
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Trademarks andregisteredtrademarks are the property of their respective owners.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781.329.4700  
Technical Support  
©2013 Analog Devices, Inc. All rights reserved.  
www.analog.com  
 
 
 
 
AD8418  
Data Sheet  
TABLE OF CONTENTS  
Features .............................................................................................. 1  
Unidirectional Operation.......................................................... 11  
Bidirectional Operation............................................................. 11  
External Referenced Output ..................................................... 12  
Splitting the Supply .................................................................... 12  
Splitting an External Reference ................................................ 12  
Applications Information .............................................................. 13  
Motor Control............................................................................. 13  
Solenoid Control ........................................................................ 14  
Outline Dimensions....................................................................... 15  
Ordering Guide .......................................................................... 16  
Automotive Products................................................................. 16  
Applications....................................................................................... 1  
General Description......................................................................... 1  
Functional Block Diagram .............................................................. 1  
Revision History ............................................................................... 2  
Specifications..................................................................................... 3  
Absolute Maximum Ratings............................................................ 4  
ESD Caution.................................................................................. 4  
Pin Configuration and Function Descriptions............................. 5  
Typical Performance Characteristics ............................................. 6  
Theory of Operation ...................................................................... 10  
Output Offset Adjustment............................................................. 11  
REVISION HISTORY  
9/13—Revision 0: Initial Version  
Rev. 0 | Page 2 of 16  
 
Data Sheet  
AD8418  
SPECIFICATIONS  
TA = −40°C to +125°C (operating temperature range), VS = 5 V, unless otherwise noted.  
Table 2.  
Parameter  
Test Conditions/Comments  
Min  
−8  
Typ  
Max  
Unit  
GAIN  
Initial  
Error Over Temperature  
Gain vs. Temperature  
VOLTAGE OFFSET  
20  
V/V  
%
ppm/°C  
Specified temperature range  
0.15  
+8  
Offset Voltage, Referred to the Input (RTI)  
Over Temperature (RTI)  
Offset Drift  
25°C  
200  
µV  
µV  
µV/°C  
Specified temperature range  
400  
+1  
−1  
+0.1  
130  
INPUT  
Input Bias Current  
Input Voltage Range  
Common-Mode Rejection Ratio (CMRR)  
µA  
V
dB  
dB  
Common mode, continuous  
Specified temperature range, f = dc  
f = dc to 10 kHz  
−2  
90  
+70  
100  
86  
OUTPUT  
Output Voltage Range  
Output Resistance  
RL = 25 kΩ  
0.015  
VS − 0.020  
V
2
DYNAMIC RESPONSE  
Small Signal −3 dB Bandwidth  
Slew Rate  
250  
1
kHz  
V/µs  
NOISE  
0.1 Hz to 10 Hz (RTI)  
2.3  
µV p-p  
Spectral Density, 1 kHz (RTI)  
OFFSET ADJUSTMENT  
Ratiometric Accuracy1  
Accuracy, Referred to the Output (RTO)  
Output Offset Adjustment Range  
POWER SUPPLY  
110  
nV/√Hz  
Divider to supplies  
Voltage applied to VREF1 and VREF2 in parallel  
VS = 5 V  
0.4995  
0.015  
2.7  
0.5005  
1
VS − 0.020  
V/V  
mV/V  
V
Operating Range  
5.5  
2.6  
V
mA  
dB  
Quiescent Current Over Temperature  
Power Supply Rejection Ratio  
Temperature Range  
VOUT = 0.1 V dc  
80  
For Specified Performance  
Operating temperature range  
−40  
+125  
°C  
1 The offset adjustment is ratiometric to the power supply when VREF1 and VREF2 are used as a divider between the supplies.  
Rev. 0 | Page 3 of 16  
 
 
AD8418  
Data Sheet  
ABSOLUTE MAXIMUM RATINGS  
Table 3.  
Stresses above those listed under Absolute Maximum Ratings  
may cause permanent damage to the device. This is a stress  
rating only; functional operation of the device at these or any  
other conditions above those indicated in the operational  
section of this specification is not implied. Exposure to absolute  
maximum rating conditions for extended periods may affect  
device reliability.  
Parameter  
Rating  
Supply Voltage  
6 V  
Input Voltage Range  
Continuous  
Survival  
Differential Input Survival  
Reverse Supply Voltage  
ESD Human Body Model (HBM)  
Operating Temperature Range  
Storage Temperature Range  
Output Short-Circuit Duration  
−2 V to +70 V  
−4 V to +85 V  
5.5 V  
0.3 V  
2000 V  
−40°C to +125°C  
−65°C to +150°C  
Indefinite  
ESD CAUTION  
Rev. 0 | Page 4 of 16  
 
 
Data Sheet  
AD8418  
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS  
–IN  
1
2
3
4
8
7
6
5
+IN  
AD8418  
GND  
V
V
1
REF  
S
TOP VIEW  
V
2
REF  
(Not to Scale)  
NC  
OUT  
NC = NO CONNECT. DO NOT  
CONNECT TO THIS PIN.  
Figure 2. Pin Configuration  
Table 4. Pin Function Descriptions  
Pin No.  
Mnemonic  
Description  
1
2
3
4
5
6
7
8
−IN  
GND  
Negative Input.  
Ground.  
Reference Input 2.  
No Connect. Do not connect to this pin.  
Output.  
Supply.  
Reference Input 1.  
Positive Input.  
VREF2  
NC  
OUT  
VS  
VREF1  
+IN  
Rev. 0 | Page 5 of 16  
 
AD8418  
Data Sheet  
TYPICAL PERFORMANCE CHARACTERISTICS  
10  
40  
30  
8
20  
6
10  
4
0
2
–10  
–20  
–30  
–40  
–50  
–60  
–70  
0
–2  
–4  
–6  
–8  
–10  
40  
25  
10  
5
20  
35  
50  
65  
80  
95 110 125  
1k  
10k  
100k  
1M  
10M  
TEMPERATURE (°C)  
FREQUENCY (Hz)  
Figure 3. Typical Offset Drift vs. Temperature  
Figure 6. Typical Small Signal Bandwidth (VOUT = 200 mV p-p)  
20  
18  
16  
14  
12  
10  
8
110  
100  
90  
80  
70  
60  
50  
6
4
2
0
–2  
0
5
10  
15  
20  
25  
30  
35  
40  
10  
100  
1k  
10k  
100k  
1M  
DIFFERENTIAL INPUT VOLTAGE (mV)  
FREQUENCY (Hz)  
Figure 7. Total Output Error vs. Differential Input Voltage  
Figure 4. Typical CMRR vs. Frequency  
0.5  
0.4  
500  
400  
V
= 5V  
S
NORMALIZED AT 25°C  
0.3  
300  
0.2  
200  
+IN  
–IN  
0.1  
100  
0
0
–0.1  
–0.2  
–0.3  
–0.4  
–0.5  
–100  
–200  
–300  
–400  
–500  
–4  
0
4
8
12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80  
(V)  
–40 –25 –10  
5
20  
35  
50  
65  
80  
95 110 125  
V
CM  
TEMPERATURE (°C)  
Figure 8. Bias Current per Input Pin vs. Common-Mode Voltage (VCM  
)
Figure 5. Typical Gain Error vs. Temperature  
Rev. 0 | Page 6 of 16  
 
Data Sheet  
AD8418  
2.0  
1.9  
1.8  
1.7  
1.6  
1.5  
1.4  
1.3  
1.2  
1.1  
1.0  
25mV/DIV  
V
= 5V  
S
INPUT  
500mV/DIV  
V
= 2.7V  
OUTPUT  
S
V
= 2.7V  
S
–5  
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80  
INPUT COMMON-MODE VOLTAGE (V)  
TIME (1µs/DIV)  
Figure 9. Supply Current vs. Input Common-Mode Voltage  
Figure 12. Fall Time (VS = 2.7 V)  
INPUT  
25mV/DIV  
INPUT  
25mV/DIV  
500mV/DIV  
OUTPUT  
OUTPUT  
500mV/DIV  
V
= 5V  
S
V
= 2.7V  
S
TIME (1µs/DIV)  
TIME (1µs/DIV)  
Figure 13. Fall Time (VS = 5 V)  
Figure 10. Rise Time (VS = 2.7 V)  
INPUT  
INPUT  
100mV/DIV  
25mV/DIV  
OUTPUT  
OUTPUT  
1V/DIV  
500mV/DIV  
V
= 2.7V  
V
= 5V  
S
S
TIME (1µs/DIV)  
TIME (1µs/DIV)  
Figure 14. Differential Overload Recovery, Rising (VS = 2.7 V)  
Figure 11. Rise Time (VS = 5 V)  
Rev. 0 | Page 7 of 16  
AD8418  
Data Sheet  
INPUT  
100mV/DIV  
OUTPUT  
200mV/DIV  
OUTPUT  
40V/DIV  
INPUT COMMON MODE  
2V/DIV  
V
= 5V  
S
TIME (1µs/DIV)  
TIME (4µs/DIV)  
Figure 15. Differential Overload Recovery, Rising (VS = 5 V)  
Figure 18. Input Common-Mode Step Response (VS = 5 V, Inputs Shorted)  
70  
60  
100mV/DIV  
50  
5V  
40  
INPUT  
2.7V  
1V/DIV  
30  
20  
10  
0
OUTPUT  
V
= 2.7V  
S
–40 –25 –10  
5
20  
35  
50  
65  
80  
95 110 125  
TIME (1µs/DIV)  
TEMPERATURE (°C)  
Figure 16. Differential Overload Recovery, Falling (VS = 2.7 V)  
Figure 19. Maximum Output Sink Current vs. Temperature  
35  
30  
25  
20  
15  
10  
5
200mV/DIV  
5V  
INPUT  
2.7V  
2V/DIV  
OUTPUT  
0
V
= 5V  
S
–40 –25 –10  
5
20  
35  
50  
65  
80  
95 110 125  
TIME (1µs/DIV)  
TEMPERATURE (°C)  
Figure 17. Differential Overload Recovery, Falling (VS = 5 V)  
Figure 20. Maximum Output Source Current vs. Temperature  
Rev. 0 | Page 8 of 16  
Data Sheet  
AD8418  
0
–50  
0.4  
0.3  
–100  
–150  
–200  
–250  
–300  
–350  
–400  
–450  
–500  
0.2  
0.1  
0
–0.1  
–0.2  
–0.3  
–0.4  
0
1
2
3
4
5
6
7
8
9
10  
–40 –25 –10  
5
20  
35  
50  
65  
80  
95 110 125  
OUTPUT SOURCE CURRENT (mA)  
TEMPERATURE (°C)  
Figure 21. Output Voltage Range from Positive Rail vs. Output Source Current  
Figure 24. CMRR vs. Temperature  
200  
180  
160  
140  
120  
100  
80  
1800  
1500  
1200  
900  
600  
300  
0
60  
40  
20  
0
1
2
3
4
5
6
7
8
9
10  
–8  
–6  
–4  
–2  
0
2
4
6
8
OUTPUT SINK CURRENT (mA)  
GAIN ERROR DRIFT (PPM/°C)  
Figure 22. Output Voltage Range from Ground vs. Output Sink Current  
Figure 25. Gain Drift Distribution  
+125°C  
+25°C  
–40°C  
V
= 5V  
S
1800  
1500  
1200  
900  
600  
300  
0
–400  
–300  
–200  
–100  
0
100  
200  
300  
400  
V
(µV)  
OS  
Figure 23. Offset Voltage Distribution  
Rev. 0 | Page 9 of 16  
AD8418  
Data Sheet  
THEORY OF OPERATION  
The AD8418 is a single-supply, zero drift, difference amplifier  
that uses a unique architecture to accurately amplify small  
differential current shunt voltages in the presence of rapidly  
changing common-mode voltages.  
The reference inputs, VREF1 and VREF2, are tied through 100 kΩ  
resistors to the positive input of the main amplifier, which allows  
the output offset to be adjusted anywhere in the output operating  
range. The gain is 1 V/V from the reference pins to the output  
when the reference pins are used in parallel. When the pins are  
used to divide the supply, the gain is 0.5 V/V.  
In typical applications, the AD8418 is used to measure current  
by amplifying the voltage across a shunt resistor connected to its  
inputs by a gain of 20 V/V (see Figure 26).  
The AD8418 offers breakthrough performance without  
compromising any of the robust application needs typical of  
solenoid or motor control. The ability to reject PWM input  
common-mode voltages and the zero drift architecture  
providing low offset and offset drift allows the AD8418 to  
deliver total accuracy for these demanding applications.  
The AD8418 is designed to provide excellent common-mode  
rejection, even with PWM common-mode inputs that can change  
at very fast rates, for example, 1 V/ns. The AD8418 contains  
patented technology to eliminate the negative effects of such  
fast changing external common-mode variations.  
The AD8418 features an input offset drift of less than 500 nV/°C.  
This performance is achieved through a novel zero drift  
architecture that does not compromise bandwidth, which is  
typically rated at 250 kHz.  
V
= –2V TO +70V  
V = 2.7V TO 5.5V  
S
CM  
70V  
V
V
1
REF  
S
V
OUT  
V
V
S
AD8418  
CM  
0V  
+IN  
–IN  
EMI  
+
FILTER  
I
SHUNT  
OUT  
G = 20  
R
SHUNT  
V /2  
S
EMI  
FILTER  
50A  
SHUNT  
–50A  
I
0V  
GND  
V
2
REF  
Figure 26. Typical Application  
Rev. 0 | Page 10 of 16  
 
 
Data Sheet  
AD8418  
OUTPUT OFFSET ADJUSTMENT  
VS Referenced Output  
The output of the AD8418 can be adjusted for unidirectional or  
bidirectional operation.  
This mode is set when both reference pins are tied to the positive  
supply. It is typically used when the diagnostic scheme requires  
detection of the amplifier and the wiring before power is applied to  
the load (see Figure 28).  
UNIDIRECTIONAL OPERATION  
Unidirectional operation allows the AD8418 to measure currents  
through a resistive shunt in one direction. The basic modes for  
unidirectional operation are ground referenced output mode  
and VS referenced output mode.  
V
S
AD8418  
R1  
For unidirectional operation, the output can be set at the negative  
rail (near ground) or at the positive rail (near VS) when the  
differential input is 0 V. The output moves to the opposite rail  
when a correct polarity differential input voltage is applied. The  
required polarity of the differential input depends on the output  
voltage setting. If the output is set at the positive rail, the input  
polarity needs to be negative to move the output down. If the  
output is set at ground, the polarity must be positive to move  
the output up.  
R4  
R3  
+
–IN  
+IN  
OUT  
R2  
V
1
2
REF  
V
REF  
GND  
Figure 28. VS Referenced Output  
Ground Referenced Output  
When using the AD8418 in this mode, both referenced inputs are  
tied to ground, which causes the output to sit at the negative rail  
when there are zero differential volts at the input (see Figure 27).  
BIDIRECTIONAL OPERATION  
Bidirectional operation allows the AD8418 to measure currents  
through a resistive shunt in two directions.  
V
S
In this case, the output is set anywhere within the output range.  
Typically, it is set at half-scale for equal range in both directions.  
In some cases, however, it is set at a voltage other than half scale  
when the bidirectional current is nonsymmetrical.  
AD8418  
R1  
R4  
R3  
+
–IN  
+IN  
OUT  
Adjusting the output is accomplished by applying voltage(s) to  
the referenced inputs.  
R2  
V
V
1
2
REF  
REF  
V
REF1 and VREF2 are tied to internal resistors that connect to an  
internal offset node. There is no operational difference between  
the pins.  
GND  
Figure 27. Ground Referenced Output  
Rev. 0 | Page 11 of 16  
 
 
 
 
 
AD8418  
Data Sheet  
V
S
EXTERNAL REFERENCED OUTPUT  
Tying both pins together and to a reference produces an output  
equal to the reference voltage when there is no differential input  
(see Figure 29). The output moves down from the reference  
voltage when the input is negative, relative to the −IN pin, and  
up when the input is positive, relative to the −IN pin.  
AD8418  
R1  
R4  
R3  
+
–IN  
+IN  
OUT  
R2  
V
S
V
V
1
2
REF  
REF  
AD8418  
R1  
GND  
R4  
R3  
+
–IN  
+IN  
OUT  
Figure 30. Split Supply  
R2  
V
V
1
2
REF  
REF  
SPLITTING AN EXTERNAL REFERENCE  
The internal reference resistors can be used to divide an external  
reference by 2 with an accuracy of approximately 0.5%. Splitting  
an external reference can be done by connecting one VREFx pin to  
ground and the other VREFX pin to the reference (see Figure 31).  
2.5V  
GND  
Figure 29. External Referenced Output  
V
S
SPLITTING THE SUPPLY  
By tying one reference pin to VS and the other to the ground pin,  
the output is set at half of the supply when there is no differential  
input (see Figure 30). The benefit is that an external reference  
is not required to offset the output for bidirectional current  
measurement. Tying one reference pin to VS and the other to  
the ground pin creates a midscale offset that is ratiometric to  
the supply, which means that if the supply increases or decreases,  
the output remains at half the supply. For example, if the supply  
is 5.0 V, the output is at half scale or 2.5 V. If the supply increases by  
10% (to 5.5 V), the output goes to 2.75 V.  
AD8418  
R1  
R4  
R3  
+
–IN  
+IN  
OUT  
R2  
V
V
1
2
REF  
REF  
5V  
GND  
Figure 31. Split External Reference  
Rev. 0 | Page 12 of 16  
 
 
 
 
 
 
Data Sheet  
AD8418  
APPLICATIONS INFORMATION  
referenced op amp because ground is not typically a stable  
MOTOR CONTROL  
reference voltage in this type of application. The instability of  
the ground reference causes inaccuracies in the measurements  
that can be made with a simple ground referenced op amp. The  
AD8418 measures current in both directions as the H-bridge  
switches and the motor changes direction. The output of the  
AD8418 is configured in an external referenced bidirectional  
mode (see the Bidirectional Operation section).  
3-Phase Motor Control  
The AD8418 is ideally suited for monitoring current in 3-phase  
motor applications.  
The 250 kHz typical bandwidth of the AD8418 allows  
instantaneous current monitoring. Additionally, the typical  
low offset drift of 0.1 µV/°C means that the measurement error  
between the two motor phases is at a minimum over temperature.  
The AD8418 rejects PWM input common-mode voltages in the  
−2 V to +70 V (with a 5 V supply) range. Monitoring the current  
on the motor phase allows sampling of the current at any point  
and provides diagnostic information such as a short to GND  
and battery. Refer to Figure 33 for the typical phase current  
measurement setup with the AD8418.  
CONTROLLER  
5V  
+IN  
V
OUT  
NC  
V
1
S
REF  
MOTOR  
AD8418  
5V  
SHUNT  
–IN GND  
V
2
REF  
2.5V  
H-Bridge Motor Control  
Another typical application for the AD8418 is as part of the  
control loop in H-bridge motor control. In this case, the shunt  
resistor is placed in the middle of the H-bridge so that it can  
accurately measure current in both directions by using the  
shunt available at the motor (see Figure 32). Using an amplifier  
and shunt in this location is a better solution than a ground  
Figure 32. H-Bridge Motor Control  
V+  
M
I
I
I
U
V
W
V–  
5V  
5V  
INTERFACE  
AD8214  
CIRCUIT  
AD8418  
AD8418  
OPTIONAL  
PART FOR  
OVERCURRENT  
PROTECTION AND  
FAST (DIRECT)  
SHUTDOWN OF  
POWER STAGE  
CONTROLLER  
BIDIRECTIONAL CURRENT MEASUREMENT  
REJECTION OF HIGH PWM COMMON-MODE VOLTAGE (–2V TO +70V)  
AMPLIFICATION  
HIGH OUTPUT DRIVE  
Figure 33. 3-Phase Motor Control  
Rev. 0 | Page 13 of 16  
 
 
 
 
AD8418  
Data Sheet  
5V  
SOLENOID CONTROL  
High-Side Current Sense with a Low-Side Switch  
SWITCH  
OUTPUT  
In the case of a high-side current sense with a low-side switch,  
the PWM control switch is ground referenced. An inductive  
load (solenoid) is tied to a power supply. A resistive shunt is  
placed between the switch and the load (see Figure 34). An  
advantage of placing the shunt on the high side is that the entire  
current, including the recirculation current, can be measured  
because the shunt remains in the loop when the switch is off. In  
addition, diagnostics can be enhanced because shorts to ground  
can be detected with the shunt on the high side.  
+
8
7
6
5
BATTERY  
AD8418  
SHUNT  
CLAMP  
DIODE  
INDUCTIVE  
LOAD  
1
2
3
4
In this circuit configuration, when the switch is closed, the  
common-mode voltage moves down to near the negative rail.  
When the switch is open, the voltage reversal across the inductive  
load causes the common-mode voltage to be held one diode  
drop above the battery by the clamp diode.  
NC = NO CONNECT.  
Figure 35. High-Side Switch  
High Rail Current Sensing  
In the high rail, current sensing configuration, the shunt resistor is  
referenced to the battery. High voltage is present at the inputs of  
the current sense amplifier. When the shunt is battery referenced,  
the AD8418 produces a linear ground referenced analog output.  
Additionally, the AD8214 can be used to provide an overcurrent  
detection signal in as little as 100 ns (see Figure 36). This feature  
is useful in high current systems where fast shutdown in  
overcurrent conditions is essential.  
5V  
OUTPUT  
CLAMP  
DIODE  
INDUCTIVE  
LOAD  
+
8
7
6
5
BATTERY  
SHUNT  
AD8418  
OVERCURRENT  
DETECTION (<100ns)  
SWITCH  
1
2
3
4
OUTPUT  
8
7
6
5
NC = NO CONNECT.  
AD8214  
Figure 34. Low-Side Switch  
High-Side Current Sense with a High-Side Switch  
1
2
3
4
The high-side current sense with a high-side switch configuration  
minimizes the possibility of unexpected solenoid activation and  
excessive corrosion (see Figure 35). In this case, both the switch  
and the shunt are on the high side. When the switch is off, the  
battery is removed from the load, which prevents damage from  
potential shorts to ground while still allowing the recirculating  
current to be measured and to provide diagnostics. Removing the  
power supply from the load for the majority of the time minimizes  
the corrosive effects that can be caused by the differential  
voltage between the load and ground.  
CLAMP  
DIODE  
SHUNT  
+
+IN  
–IN  
1
2
3
4
8
7
6
5
INDUCTIVE  
LOAD  
V
V
1
GND  
REF  
S
AD8418  
V
2
TOP VIEW  
REF  
(Not to Scale)  
5V  
NC  
OUT  
SWITCH  
When using a high-side switch, the battery voltage is connected  
to the load when the switch is closed, causing the common-mode  
voltage to increase to the battery voltage. In this case, when the  
switch is open, the voltage reversal across the inductive load  
causes the common-mode voltage to be held one diode drop  
below ground by the clamp diode.  
NC = NO CONNECT.  
Figure 36. High Rail Current Sensing  
Rev. 0 | Page 14 of 16  
 
 
 
 
Data Sheet  
AD8418  
OUTLINE DIMENSIONS  
5.00 (0.1968)  
4.80 (0.1890)  
8
1
5
4
6.20 (0.2441)  
5.80 (0.2284)  
4.00 (0.1574)  
3.80 (0.1497)  
0.50 (0.0196)  
0.25 (0.0099)  
1.27 (0.0500)  
BSC  
45°  
1.75 (0.0688)  
1.35 (0.0532)  
0.25 (0.0098)  
0.10 (0.0040)  
8°  
0°  
0.51 (0.0201)  
0.31 (0.0122)  
COPLANARITY  
0.10  
1.27 (0.0500)  
0.40 (0.0157)  
0.25 (0.0098)  
0.17 (0.0067)  
SEATING  
PLANE  
COMPLIANT TO JEDEC STANDARDS MS-012-AA  
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS  
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR  
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.  
Figure 37. 8-Lead Standard Small Outline Package [SOIC_N]  
Narrow Body  
(R-8)  
Dimensions shown in millimeters and (inches)  
3.20  
3.00  
2.80  
8
1
5
4
5.15  
4.90  
4.65  
3.20  
3.00  
2.80  
PIN 1  
IDENTIFIER  
0.65 BSC  
0.95  
0.85  
0.75  
15° MAX  
1.10 MAX  
0.80  
0.55  
0.40  
0.15  
0.05  
0.23  
0.09  
6°  
0°  
0.40  
0.25  
COPLANARITY  
0.10  
COMPLIANT TO JEDEC STANDARDS MO-187-AA  
Figure 38. 8-Lead Mini Small Outline Package [MSOP]  
(RM-8)  
Dimensions shown in millimeters  
Rev. 0 | Page 15 of 16  
 
AD8418  
Data Sheet  
ORDERING GUIDE  
Model1, 2  
Temperature Range  
−40°C to +125°C  
−40°C to +125°C  
−40°C to +125°C  
−40°C to +125°C  
−40°C to +125°C  
−40°C to +125°C  
Package Description  
8-Lead MSOP  
8-Lead MSOP, 13Tape and Reel  
8-Lead MSOP  
8-Lead MSOP, 13Tape and Reel  
8-Lead SOIC_N  
8-Lead SOIC_N, 13Tape and Reel  
Package Option  
Branding  
AD8418BRMZ  
RM-8  
RM-8  
RM-8  
RM-8  
R-8  
Y4N  
Y4N  
Y4M  
Y4M  
AD8418BRMZ-RL  
AD8418WBRMZ  
AD8418WBRMZ-RL  
AD8418WBRZ  
AD8418WBRZ-RL  
R-8  
1 Z = RoHS Compliant Part.  
2 W = Qualified for Automotive Applications.  
AUTOMOTIVE PRODUCTS  
The AD8418W models are available with controlled manufacturing to support the quality and reliability requirements of automotive  
applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers  
should review the Specifications section of this data sheet carefully. Only the automotive grade products shown are available for use in  
automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to  
obtain the specific Automotive Reliability reports for these models.  
©2013 Analog Devices, Inc. All rights reserved. Trademarks and  
registered trademarks are the property of their respective owners.  
D11546-0-9/13(0)  
Rev. 0 | Page 16 of 16  
 
 
 
 

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