LT1999-10 Datasheet, PDF (19/24 Pages) Linear Technology – High Voltage, Bidirectional Current Sense Amplifier Low Power Shutdown <10μA

LT1999-10/LT1999-20/
LT1999-50
Typical Applications
Solenoid Current Monitor
The solenoid of Figure 7 consists of a coil of wire in an
iron case with permeable plunger that acts as a movable
element. When the MOSFET turns on, the diode is reversed
biased off, and current flows through R_SENSE to actuate
the solenoid. If the MOSFET is turned off, the current
in the MOSFET is interrupted, but the energy stored in
the solenoid causes the diode to turn on and current to
freewheel in the loop consisting of the diode, R_SENSE and
the solenoid.
Figure 7 shows the LT1999 monitoring currents in a
ground referenced solenoid used when the coil is hard
tied to the case, and is tied to ground. Figure 8 shows a
supply referenced solenoid whose coil is insulated from
the case. The LT1999 will interface equally well to either
of these two configurations.
Bidirectional PWM Motor Monitor
Pulse width modulation is commonly used to efficiently
vary the average voltage applied across a DC motor. The
H-bridge topology of Figure 9 allows full 4-quadrant control:
clockwise control, counter-clockwise control, clockwise
regeneration, and counter-clockwise regeneration. The
LT1999 in conjunction with a non-inductive current shunt
is used to monitor currents in the rotor. The LT1999 can
be used to detect stuck rotors, provide detection of over-
current conditions in general, or provide current mode
feedback control.
Figure 10 shows a plot of the output voltage of the LT1999.
V_S
OFF
ON
5V
V⁺
1
V_+IN
2
4k
V⁺
R_SENSE
V_–IN
3
4k
5V
V⁺
SOLENOID
4
0.1µF
LT1999
SHDN
+
–
0.8k
0.8k
V⁺
2µA
8 _VSHDN
R_G
–
+
V⁺
7 _VOUT
160k
6 ^VREF
160k
0.1µF
5
1999 F07a
V_OUT
SOLENOID RELEASES
SOLENOID PLUNGER PULLS IN
V_+IN
TIME (50ms/DIV)
Figure 7. Solenoid Current Monitor for Ground Tied Solenoid. The Common Mode
Inputs to the LT1999 Switch Between V_S and One Diode Drop Below Ground
2.5V
1999 F07b
1999fb
19