SYNC

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

LS8397s. This eliminates the need for RC components for any

other

LS8397 controllers used in the system. As an input the

sync can be driven by the

LS8397 that has the RC oscillator

components or by any other system external clock.

PHA/PHB/PHC/PHD

Phase drive output signals for power stages. In a Bipolar motor

PHA and PHB are used for one H-bridge while PHC and PHD

are used for the other.

INH1/INH2 Outputs

These outputs are active low inhibit controls for motor drive

outputs. INH1 controls driver stage using PHA and PHB sig-

nals while INH2 control driver stage using PHC and PHD sig-

nals. When the Control input is low, these outputs are chopped

using the internal oscillator for current regulating.

CONTROL Input

When high, the phase outputs, PHA, PHB, PHC and PHD are

chopped. When low, INH1 and INH2 are chopped. Normally,

inhibit outputs are chopped. Phase chopping might be used

with a Bipolar motor that does not store much energy to pre-

vent fast current decay and a low useful torque.

ENABLE Input

When Enable input is low, INH1, INH2, PHA, PHB, PHC and

PHD are brought low.

HOME Output

An open drain output that indicates when the

LS8397 is in its

initial state with PHA, PHB, PHC, PHD = logic states 0101 re-

spectively. Refer to Figure 4. In the active state the open

drain device is off.

STEP Input

An active low pulse on this input causes the motor to advance

one step. The step occurs on the rising edge of the step signal.

FRD/REV Input

A logic 1 on this input causes the motor to advance through

the stepping sequence of Fig. 4. A logic 0 on this input cause

the motor to reverse the sequence.

RESET Input

An active low on this input cause the motor to be restored to

the home position (0101).

HALF/FULL Input

When high, half-step operation is selected. When low, full-step

operation is selected. The one-phase-on full step is selected

by selecting full when the stepping sequence is at an even

state. The two-phase-on full step operation is selected when

the stepping sequence is at an odd state. Refer to Figure 4.

SENSE1/ SENSE2 Inputs

Inputs for load current sense voltages from power stages using

PHA and PHB drive signals or PHC and PHD drive signals,

respectively.

When holding-torque mode is enabled, the motor torque is

switched to stepping torque at a step command followed by

holding torque after a programmable delay. The stepping torque

is controlled by the reference voltage VREFs input and the hold-

ing torque is controlled by the voltage at the VREFh input. The

delay is controlled by a resistor-capacitor pair connected to the

RC pin.

When the holding-torque mode is disabled, the motor torque re-

mains in the stepping torque mode all the time controlled by the

VREFs voltage.

RC Input/Output

A resistor-capacitor pair connected to this pin starts a time-out

delay at every step command. At the start of the delay, the ref-

erence voltage at the VREFs pin is switched in for the SENSE

comparators to produce higher stepping torque. At the end of

the time-out, the reference voltage at the VREFh pin is switched

in for the SENSE comparators to produce the lower holding

torque, reducing power dissipation while the motor is stationary.

The delay is given by Tds = 1.4RC

If tied low, holding torque mode is disabled and stepping torque

is produced in both dynamic and static states by using the

VREFs reference voltage.

VREFs Input

Input for the SENSE comparator reference voltage for produc-

ing stepping torque.

VREFh Input

Input for the SENSE comparator reference voltage for produc-

ing holding torque.

CT_EN Input

Input for selecting/deselecting compensated torque-ripple

mode. The step sequence in the half-step mode alternates be-

tween one-phase-on and two-phase-on states resulting in

torque ripple during the stepping sequence. In the compensat-

ed-torque mode, the ripple is eliminated by equalizing the

torques for the alternate states. This is done by alternately

switching the SENSE reference voltages between 100% and

70.7% in alternate cycles.

The CT_EN input is relevant only in the half-step mode, since

the alternating one-step-on and two-step-on sequence does not

exist in the full-step mode.

This input has an internal pull-up.

8397-011409-2