MP6601 – 35V, 2.5A, STEPPER MOTOR DRIVER W/ INTERNAL CURRENT SENSE

MP6601 Rev. 1.01

www.MonolithicPower.com

10

9/4/2018

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© 2018 MPS. All Rights Reserved.

OPERATION

The MP6601 is a bipolar stepper motor driver

that

integrates

eight

N-Channel

power

MOSFETs comprised of two internal full-bridges

with 2.5A of current capability. The MP6601

operates over a wide supply voltage range of

4.5 - 35V.

The MP6601 is designed to operate bipolar

stepper motors in full-, half-, and quarter-step

modes. The current of each full-bridge is set by

the output voltage of an internal DAC, which is

controlled by the xI0 and xI1 input pins.

The currents in each of the two outputs are

regulated with programmable, constant off-time,

pulse-width modulation (PWM) control circuitry.

The MP6601 integrates internal current sensing,

eliminating the need for external sense resistors.

Input Interface

The MP6601 contains two full H-bridges that

operate independently. Each H-bridge has an

input signal that controls the current flow

direction in the H-bridge (see Table 1).

Table 1: Input Control Truth Table

xPHASE

xOUT1

xOUT2

0

L

H

1

H

L

Additionally, each H-bridge has two input pins

that are used to scale the current regulation

point in the bridge (see Table 2).

Table 2: Current Regulator Sensing

xI1

xI0

Current

0

0

100%

0

1

71%

1

0

38%

1

1

0% (high impedance)

Programmable Constant Off-Time Current

Control

The

motor

current

is

regulated

by

a

programmable constant off-time PWM current

control circuit. Its operation is described below:

 Initially, a diagonal pair of MOSFETs turns

on and drives current through the motor

winding.

 The current increases in the motor winding,

which is sensed by an internal current-

sense circuit. During the initial blanking time

always turns on in spite of current-limit

detection.

 When the current reaches the current trip

threshold, the internal current comparator

either shuts off the HS-FET so the winding

inductance current freewheels through the

two low-side MOSFETs (LS-FET) (slow

decay) or turns on another diagonal pair of

MOSFETs so the current flows back to the

input (fast decay).

 The current keeps decreasing for the

constant off-time unless a zero current level

is detected. Afterward, the HS-FET is

enabled to increase the winding current

again.

 The cycle then repeats.

be approximated with Equation (1):

OFF

t

t(ns) 190 R (k )





(1)

The full-scale (100%) regulation current can be

calculated with Equation (2):





Max

ISET

I71k / R

(2)

Blanking Time

There is usually a current spike during the

switching transition due to the body diode’s

reverse-recovery current or the distributed

inductance or capacitance. 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 MP6601 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

period

drops

below

the

threshold,