Typical Applications

BASIC MOTOR DRIVER

The LMD18201 can directly interface to any Sign/Magnitude

PWM controller. The LM629 is a motion control processor

that outputs a Sign/Magnitude PWM signal to coordinate ei-

ther positional or velocity control of DC motors. The

LMD18201 provides fully protected motor driver stage.

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 resis-

tor 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 7). This resistor should have a value of 0.1

Ω or less to

stay within the allowable voltage compliance of the sense

pin, particularly at higher operating current levels. The volt-

age between power ground/sense (Pin 7) and the signal

ground (Pin 8) must stay within the range of −1V to +0.5V. In-

ternally there is approximately 25

Ω between pins 7 and 8

and this resistance will slightly reduce the value of the exter-

nal sense resistor. Approximately 70% of the quiescent sup-

ply 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 in-

ternal 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.

DS010793-10

FIGURE 6. Basic Motor Driver

DS010793-11

FIGURE 7. Current Sensing

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