MP6520

– 32V, 1.5A, MICROSTEPPING MOTOR DRIVER W/ INTEGRATED MOSFETS

MP6520 Rev. 1.0

www.MonolithicPower.com

9

10/10/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP6520 is a bipolar stepper motor driver

that

integrates

eight

N-channel

power

MOSFETs arranged as two full bridges with

translator logic to drive a bipolar stepper motor.

It can supply up to 1.5A of current over a wide

8V to 32V input voltage range. The MP6520 is

designed to operate bipolar stepper motors in

full-, half-, quarter-, and eighth-step modes. The

current in each of the two output bridges is

regulated with programmable, constant off-time

pulse-width modulation (PWM) control circuitry.

At each step, the current for each full bridge is

set by the value of its external current sense

output voltage of its DAC, which is controlled by

the output of the translator.

Stepping

The motor moves step-by-step by applying a

series of pulses to STEP. A rising edge on the

STEP input sequences the translator one

increment in the direction set by the level of the

DIR input. The translator controls the input to

the DACs and the direction of current flow in

each winding. The amplitude of the increment is

determined by the state of the inputs MS1 and

MS2 (see Table 2).

Figure

2

and

Table

1

show

the

timing

requirements of the STEP, DIR, MS1, and MS2

inputs.

STEP

MSx, DIR

Figure 2: Input Logic Timing

Table 1: Input Logic Timing

Time Duration

Symbol

Typ.

Unit

Step

minimum

high

pulse width

1

µs

Step

minimum

low

pulse width

1

µs

Set-up

time,

input

change to STEP

200

ns

Hold time, input change

to STEP

200

ns

The motor winding currents are regulated by a

programmable, constant-off-time, PWM, current

control circuit, which operates as follows:

1. Initially, a diagonal pair of MOSFETs turns

on so current can flow through the motor

winding.

2. The current increases in the motor winding,

which is sensed by an external sense

turns on regardless of current limit detection.

the current regulation threshold, the internal

current comparator either shuts off the high-

side MOSFET so the winding inductance

current freewheels through the two low-side

MOSFETs (slow decay), or turns on the

opposite diagonal pair of MOSFETs so the

current flows back to the input (fast decay).

4. The current continues decreasing for the

constant off-time.

5. The cycle repeats.

be approximated with Equation (1):

OFF

t

t

(ns)

190 R (k )







(1)

The full-scale (100%) current limit threshold can

be calculated with Equation (2):

REF

Max LIMIT

SENSE

V

I

5R







(2)

current sense comparator in precise steps. The

calculated with Equation (3):

Trip LIMIT

Trip LIMIT Max LIMIT

I

%I

I









(3)