MP6500

– 35V, 2.5A, STEP MOTOR DRIVER W/ INTERNAL CURRENT SENSE

MP6500 Rev. 1.01

www.MonolithicPower.com

13

12/27/2017

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© 2017 MPS. All Rights Reserved.

Blanking Time

There is usually a current spike during the

switching transition due to the

body diode’s

reverse-recovery current and the distributed

winding capacitance of the motor. This current

spike requires filtering to prevent it from

erroneously shutting down the HS-FET.

After the PWM cycle begins, the output of the

current sense comparator is ignored for the

fixed blanking time. This blanking time results in

a minimum on time for the PWM cycle.

Automatic Decay Mode

The MP6500 uses a fully automatic decay

mode to provide accurate current regulation.

Initially, slow decay is used. At the end of the

threshold, then fast decay mode is initiated by

reversing the state of the H-bridge outputs.

Once the current level during this fast decay

decay is again engaged for another fixed off

time. After the completion of this second fixed

off time, a new PWM cycle begins.

Figure 3 below shows the automatic decay

mode operation during a current reduction as a

result of a step input.

Fast

Decay

Change

Slow

Decay

In some cases, specifically high voltage and low

inductance or the regulation of very small

currents, the minimum on time of the PWM

cycle (set by the blanking time described above)

can cause the current to rise very quickly. In

this case, both slow and fast decay are used

(see Figure 4).

Current regulation of low

current / low inductance

Fast

Decay

Slow

Decay

Figure 4: Current Regulation of Low Current/Low

Inductance

Microstep Selection (MS1, MS2)

The step mode is selected by applying logic

high and low voltages to the MS1 and MS2 (see

Table 1). The MP6500 supports full-, half-,

quarter-,

and

eighth-step

modes

for

progressively finer step resolution and control.

Table 1: Stepping Format

MS2

MS1

STEP Mode

L

L

Full step

L

H

Half step

H

L

Quarter step

H

H

Eighth step

Full-step mode has four states with each motor

winding

driven

with

either

70.7%

of

the

maximum positive current or 70.7% of the

maximum negative current. This provides four

steps per electrical rotation. Half-step mode

creates eight steps per electrical rotation.

Quarter- and eighth-step modes provide 16 and

32 steps per rotation respectively.

Table 2 and Figure 5 show the relative current

level sequence for different settings of MSx.

The MSx pins have internal pull-down resistors.

SLEEP, nENBL Operation

Driving nSLEEP low puts the device into a low-

power sleep state. In this state, the gate drive

charge pump is stopped, and all the internal

circuits and H-bridge outputs are disabled. All

inputs are ignored when nSLEEP is active low.

When

waking

up

from

sleep

mode,

approximately 1ms of time must pass before a

STEP command can be issued to allow the

internal circuitry to stabilize. nSLEEP has an

internal pull-down resistor.