STEPPER MOTOR CONTROLLER

FEATURES:

• Controls Bipolar and Unipolar Motors

• Cost-effective,

low current, pin compatible replacement for L297

• Torque ripple compensated half-steps

- LS8297CT

• 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)

•

Supply current < 400uA

•

LS8297 (DIP), LS8297-S (SOIC), LS8297-TS (TSSOP)

LS8297CT (DIP), LS8297CT-S (SOIC), LS8297CT-TS (TSSOP)

– See Figure 1 –

April 2009

8297-042009-1

LSI/CSI

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

LS8297

LS8297CT

DESCRIPTION:

The

LS8297 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

LS8297 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

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

pulse.

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 dis-

sipation in the load sensing resistors. Refer to Figure 5B for Bipolar mo-

tors. If PHA is high and PHB is low, current flows through Q1, motor

winding, 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 input 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

current in either half of the center tapped motor winding recir-

culates through the diode across it.

LS8297CT is the torque ripple compensated version of the

LS8297. Torque imbalance resulting from alternating “one-

phase on”, “two-phase on” sequence of the half-step mode

(see Figure 4) is eliminated in the

LS8297CT by switching the

sense reference voltage between 100% and 70.7% in alter-

nate steps.

INPUT/OUTPUT DESCRIPTION:

OSC Input

pacitor connected to ground determines the oscillator chopper

rate. When connected as an oscillator, the oscillator output

appears as a negative-going pulse at the Sync pin. If the Os-

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

Osc frequency, fosc = 1/0.69RC

SYNC

As an output the Sync can be used to drive Sync pins of other

LS8297s. This eliminates the need for RC components for

any other

LS8297 controllers used in the system. As an input

the Sync can be driven by the

LS8297 that has the RC oscilla-

tor components or by any other system external clock.

UL

®

A3800

1

FIGURE 1

2

3

4

5

6

20

19

18

17

16

15

7

8

9

10

14

13

12

11

SYNC

HOME

PHD

ENABLE

RESET

FWD/REV

OSC

VREF

SENSE1

SENSE2

CONTROL

PHA

PHC

HALF/FULL

STEP

INH2

PHB

INH1

PIN ASSIGNMENT

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