Datasheet AD8417 (Analog Devices) - 14

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AD8417 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. Tie an inductive
+ 8 7 6 BATTERY 5
load (solenoid) to a power supply and place a resistive shunt
–
between the switch and the load (see Figure 34). An advantage of placing the shunt on the high side is that the entire current,
SHUNT AD8417
including the recirculation current, is measurable because the shunt remains in the loop when the switch is off. In addition,
CLAMP INDUCTIVE 1 2 3 4
diagnostics are enhanced because shorts to ground are detected
DIODE LOAD N 2
with the shunt on the high side.
–I ND F NC G REV
In this circuit configuration, when the switch is closed, the common-mode voltage decreases to near the negative rail. When 033 1882- the switch is open, the voltage reversal across the inductive load
NC = NO CONNECT.
1 Figure 35. High-Side Switch 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 +I V V O DIODE LOAD
the AD8417 produces a linear ground referenced analog output.
+ 8 7 6 BATTERY 5
Additional y, the AD8214 provides 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
SHUNT AD8417
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.
1882- 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
minimizes the possibility of unexpected solenoid activation and
REV
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
CLAMP DIODE
potential shorts to ground while still allowing the recirculating current to be measured and to provide diagnostics. Removing
SHUNT
the power supply from the load for the majority of the time that
RY + +IN E –IN T 1 8
the switch is open minimizes the corrosive effects that can be
V INDUCTIVE – GND REF1 2 AD8417 7 LOAD BAT
caused by the differential voltage between the load and ground.
VREF2 V TOP VIEW S 3 6 (Not to Scale) 5V
When using a high-side switch, the battery voltage is connected
NC 4 5 OUT SWITCH
to the load when the switch is closed, causing the common-mode
NC = NO CONNECT.
voltage to increase to the battery voltage. In this case, when the 034 switch is open, the voltage reversal across the inductive load 11882- causes the common-mode voltage to be held one diode drop Figure 36. High Rail Current Sensing below ground by the clamp diode. Rev. E | Page 14 of 17 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION TYPICAL APPLICATION CIRCUIT REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION OUTPUT OFFSET ADJUSTMENT UNIDIRECTIONAL OPERATION Ground Referenced Output Mode VS Referenced Output Mode 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 PINOUT OPTION ENGINEERED FOR FMEA OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS