Datasheet AD8418 (Analog Devices) - 15

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AD8418 Data Sheet SOLENOID CONTROL 5V High-Side Current Sense with a Low-Side Switch SWITCH 1 F
In the case of a high-side current sense with a low-side switch,
N RE S UT OUTPUT +I V V O
the PWM control switch is ground referenced. An inductive
+ 8 7 6 BATTERY 5
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
SHUNT AD8418
current, including the recirculation current, can be measured because the shunt remains in the loop when the switch is off. In
CLAMP INDUCTIVE 1 2 3 4 DIODE
addition, diagnostics can be enhanced because shorts to ground
LOAD N 2 ND F NC
can be detected with the shunt on the high side.
–I G REV
In this circuit configuration, when the switch is closed, the 033 common-mode voltage moves down to near the negative rail.
NC = NO CONNECT.
1546- 1 When the switch is open, the voltage reversal across the inductive Figure 35. High-Side Switch load causes the common-mode voltage to be held one diode drop above the battery by the clamp diode.
High Rail Current Sensing
In the high rail, current sensing configuration, the shunt resistor is
5V
referenced to the battery. High voltage is present at the inputs of
1
the current sense amplifier. When the shunt is battery referenced,
F CLAMP INDUCTIVE N RE S UT OUTPUT
the AD8418 produces a linear ground referenced analog output.
+I V V O DIODE LOAD + 8 7 6
Additionally, the AD8214 can be used to provide an overcurrent
BATTERY 5 –
detection signal in as little as 100 ns (see Figure 36). This feature is useful in high current systems where fast shutdown in
SHUNT AD8418
overcurrent conditions is essential.
OVERCURRENT SWITCH 1 2 3 4 DETECTION (<100ns) N ND UT OUTPUT N 2 –I NC G O –I ND F NC G REV 8 7 6 5
032
NC = NO CONNECT.
1546- 1
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
S N G V +I NC RE
minimizes the possibility of unexpected solenoid activation and
V
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
CLAMP
battery is removed from the load, which prevents damage from
DIODE
potential shorts to ground while still allowing the recirculating
SHUNT
current to be measured and to provide diagnostics. Removing the
RY +
power supply from the load for the majority of the time minimizes
+IN E –IN T 1 8 V INDUCTIVE –
the corrosive effects that can be caused by the differential
GND REF1 2 AD8418 7 LOAD BAT V V
voltage between the load and ground.
REF2 TOP VIEW S 3 6 (Not to Scale) 5V NC 4 5 OUT
When using a high-side switch, the battery voltage is connected
SWITCH NC = NO CONNECT.
to the load when the switch is closed, causing the common-mode voltage to increase to the battery voltage. In this case, when the 034 switch is open, the voltage reversal across the inductive load 1546- 1 causes the common-mode voltage to be held one diode drop Figure 36. High Rail Current Sensing below ground by the clamp diode. Rev. 0 | Page 14 of 16 Document Outline Features Applications General Description Functional Block Diagram Table of Contents Revision History Specifications Absolute Maximum Ratings ESD Caution Pin Configuration and Function Descriptions Typical Performance Characteristics Theory of Operation Output Offset Adjustment Unidirectional Operation Ground Referenced Output VS Referenced Output Bidirectional Operation External Referenced Output Splitting the Supply Splitting an External Reference Applications Information Motor Control 3-Phase Motor Control H-Bridge Motor Control Solenoid Control High-Side Current Sense with a Low-Side Switch High-Side Current Sense with a High-Side Switch High Rail Current Sensing Outline Dimensions Ordering Guide Automotive Products