Datasheet

LMD18201
SNVS092D –APRIL 1998–REVISED APRIL 2013 www.ti.com
CURRENT SENSING
In many motor control applications it is desirable to sense and control the current through the motor. For these
types of applications a companion product, the LMD18200, is also available. The LMD18200 is identical to the
LMD18201 but has current sensing transistors that output a current directly proportional to the current conducted
by the two upper DMOS power devices to a separate current sense pin. This technique does not require a low
valued, power sense resistor and does not subtract from the available voltage drive to the motor.
To sense the bridge current through the LMD18201 requires the addition of a small sense resistor between the
power ground/sense pin (Pin 7) and the actual circuit ground (see Figure 15). This resistor should have a value
of 0.1Ω or less to stay within the allowable voltage compliance of the sense pin, particularly at higher operating
current levels. The voltage between power ground/sense (Pin 7) and the signal ground (Pin 8) must stay within
the range of −1V to +0.5V. Internally there is approximately 25Ω between pins 7 and 8 and this resistance will
slightly reduce the value of the external sense resistor. Approximately 70% of the quiescent supply current (10
mA) flows out of pin 7. This will cause a slight offset to the voltage across the sense resistor when the bridge is
not conducting. During reverse recovery of the internal protection diodes the voltage compliance between pins 7
and 8 may be exceeded. The duration of these spikes however are only approximately 100 ns and do not have
enough time or energy to disrupt the operation of the LMD18201.
Figure 15. Current Sensing
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