STEPPER MOTOR CONTROLLER

FEATURES:

• Controls Bipolar and Unipolar Motors

•

L297 operation with added functions:

• Selectable torque ripple compensated phase drive

• Selectable automated switching between stepping and holding torques

• Supply current < 400uA

• Half and full step modes

• Normal/wave drive

• Direction control

• Reset input

• Step control input

• Enable input

• PWM chopper circuit for current control

• Two over current sensor comparators with external references input

• All inputs and outputs TTL/CMOS compatible (TTL for 5V operation)

•

LS8397 (DIP), LS8397-S (SOIC), LS8397-TS (TSSOP)

– See Figure 1 –

April 2009

8397-042109-1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405

LS8397

DESCRIPTION:

The

LS8397 Stepper Motor Controller generates four phase drive signal

outputs for controlling two phase Bipolar and four phase Unipolar mo-

tors. The outputs are used to drive two H-bridges for the two motor

windings in the Bipolar motor or the four driver transistors for the two

center- tapped windings in the Unipolar motor. The motor can be driven

in full step mode either in normal drive (two-phase-on) or wave drive

(one-phase-on) and half step mode. The

LS8397 provides two inhibit

outputs which are used to control the driver stages of each of the motor

phases. The circuit uses STEP, FRD/REV and HALF/FULL inputs in a

translator to generate controls for the output stages.

A dual PWM chopper circuit using an on-chip oscillator, latches and volt-

age comparators are used to regulate the current in the motor windings.

For each pair of phase driver outputs (PHA, PHB, and PHC, PHD) each

pulse of the common internal oscillator sets the latch and enables the

output. If the current in the motor winding causes the voltage across a

sense resistor to exceed the reference voltage, VREFs, at the compara-

tor inputs, the latch is reset disabling the output until the next oscillator

pulse.

Input for a separate reference voltage VREFh is also provided for reduc-

ing holding torque when the motor is not turning. When holding torque

mode is enabled with a resistor-capacitor pair connected to the RC Pin,

the sense comparator input reference switches between VREFs and

VREFh depending on whether the motor is turning or not. The separate

sense reference voltages allow for conserving power when the motor is

not turning. Holding torque mode can be disabled by connecting the RC

In the half-step stepping sequence, the phase drives alternate between

one-phase-on and two-phase-on in successive steps at full power thus

generating substantial ripple on the output torque. An input, CT_EN is

provided for selecting an operational mode in which the torque ripple is

corrected. In this mode the sense input reference voltage is switched to

100% and 70.7% of the applied voltages at the VREFs and VREFh in-

puts in successive one-phase-on and two-phase-on conditions, respec-

tively. The CONTROL input determines whether the chopper acts on the

phase driver outputs or the inhibit outputs. When the phase

lines are chopped, the non-active phase line of each pair

(PHA, PHB or PHC, PHD) is activated rather than de-

activating the active line to reduce dissipation in the load sens-

ing resistor Rs. Refer to Figure 5B for Bipolar motors. If PHA

is high and PHB is low, current flows through Q1, motor wind-

ing, Q4 and sense resistor Rs. When chopping occurs, PHB is

brought high and circulating current flows through Q1 and D3

and not through Rs resulting in less power dissipation in Rs.

Current decay is slow using this method. When the Control in-

put is brought low, chopping occurs by bringing INH1 low. In

this case circulating current flows through D2, motor winding

and D3 and through the power supply to ground causing the

current to decay rapidly. For Unipolar motors, only inhibit

chopping is used. Refer to Figure 6. When INH1 is brought

low the current flowing in either half of the center tapped mo-

tor winding recirculates through the diode across it.

INPUT/OUTPUT DESCRIPTION:

OSC Input

itor connected to ground determines the oscillator chopper

rate. When connected as an oscillator, the oscillator output ap-

pears as a negative-going pulse at the Sync pin. If the oscillat-

ing pin is tied to ground, the Sync pin becomes an input.

Osc frequency, fosc = 1/0.69RC

UL

®

A3800

FIGURE 1

3

4

5

6

24

23

22

21

20

19

7

8

9

10

18

17

16

SYNC

HOME

PHD

ENABLE

RESET

FWD/REV

OSC

VREFh

SENSE1

SENSE2

CONTROL

PHA

PHC

HALF/FULL

STEP

INH2

PHB

INH1

PIN ASSIGNMENT

TOP VIEW

VREFs

12

15

13

CT_EN

14

2

1

RC

11

NC