MP6509 – 2.7V-TO-18V, 1.2A STEPPER MOTOR DRIVER

MP6509 Rev.1.0

www.MonolithicPower.com

12

8/28/2014

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the other input pin low; for slow decay mode,

apply the PWM signal to one input pin and keep

the other input pin high. See Table 2 for more

configuration details and Figure 5 for detailed

waveforms.

Table 2: PWM Control

A/BIN1

A/BIN2

Mode

H (PWM)

L

Forward

L (PWM)

L

Fast Decay

L

H (PWM)

Reverse

L

L (PWM)

Fast Decay

H

L (PWM)

Forward

H

H (PWM)

Slow Decay

L (PWM)

H

Reverse

H (PWM)

H

Slow Decay

A/B IN1

A/B IN2

Forward

Reverse

Forward

Reverse

Slow Decay

Fast Decay

0

0

0

Figure 5: External PWM Current Control Waveform

Internal PWM Current Control

For this control method, the motor current is

regulated by an internal constant off-time PWM

current control circuit as the following:

• Initially, a diagonal pair of MOSFETs

turns on so current can flow through the

motor winding.

• The current increases in the motor

winding, which is sensed by an external

MOSFET always turns on in spite of

current limit detection.

the internal reference voltage threshold

shuts off the high-side MOSFET.

• The stepper motor’s inductance causes

the current to freewheel through the two

low-side MOSFETs (slow decay).

• During this freewheeling time, the current

decreases until the internal clock reaches

its’ constant off time (typically 30µs). After

that, the high-side MOSFET is enabled to

increase the winding current again.

• The cycle then repeats.

Calculate the current limit as:

REF

LIMIT

SENSE

V

I

R

=

(1)

Figure 6: Internal PWM Current Control Waveform

settings depending on the status of the two

inputs ATT1 and ATT2. This is helpful to reduce

the power dissipation when motor holding current

is supplied. See Table 3 for more configuration

details.