MP6501A – 35V, 2.5A MICROSTEPPING MOTOR DRIVER WITH INTEGRATED FETS

MP6501A Rev. 1.11

www.MonolithicPower.com

11

8/22/2016

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OPERATION

The MP6501A is a bipolar stepper motor driver

that integrates 8 N-Channel power MOSFETs

arranged as 2 full-bridges, with 2.5A current

capability over a wide input voltage range of 8V

to 35V. It is designed to operate bipolar stepper

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

modes. The current in each of the two output

full-bridges is regulated with programmable

constant off-time PWM (pulse width modulated)

control circuitry. At each step, the current for

each full-bridge is set by the value of its

external current sense resistor, a reference

DAC which is controlled by the output of the

translator.

Stepping

The motor moves step by step by applying a

series of pulses to the STEP pin. 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 inputs MS1, MS2

and MS3 (see Table 1).

The STEP input minimum high/low pulse width

is 1us. The logic control signals MSx and DIR

require at least 200ns setup time and hold time

to the STEP rising edge.

Time Duration

Symbol

Typ.

Unit

Step

minimum

HIGH

pulse width

1

µs

Step

minimum

LOW

pulse width

1

µs

Setup time, input change

to STEP

200

ns

Hold time, input change

to STEP

200

ns

Figure 2: Logic Timing Diagram

The motor winding currents are regulated by a

programmable constant off-time PWM current

control circuit. This operates as follows:

 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 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).

 The current keeps decreasing for the

constant off-time.

 The cycle then repeats.

approximated by

OFF

t

t

(ns) 190 R (k )





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

calculated by

REF

Max LIMIT

SENSE

V

I

5R







current sense comparator in precise steps (see

Trip LIMIT

Trip LIMIT Max LIMIT

I%I

I







Microstep Select (MS1, MS2, MS3)

The step mode is selected by applying logic

high and low voltages to the MS1, MS2 and

MS3 pins as shown in Table 1. The MP6501A

supports full-, half-, quarter-, and eighth- step

modes

for

progressively

finer

step