FEATURES:

Controls Bipolar and Unipolar stepper motors

Step modes: Full, 1/2, 1/4, 1/8, 1/16 and 1/32

PWM outputs for external H-bridge drivers

Precision DAC reference for PWM sense comparators

Fast, Slow and mixed decay modes

Power saving holding torque for idling motor

Automatic switching to holding torque with

programmable delay when motor idles

Programmable delay for sense input blanking

Programmable delay for mixed decay cycles

Input for Step command

Input for Direction control

Input for Reset to HOME

Input for disabling PWM outputs

Input/output for external clock or built-in oscillator

Supply current < 400uA

Supply voltage 4.5V to 5.5V

LS8292

(DIP), LS8292-S (SOIC), LS8292-TS

(TSSOP)

LS8293

(DIP), LS8293-S (SOIC), LS8293-TS

(TSSOP)

DESCRIPTION:

LS8292

and LS8293 are stepper motor controllers with

selectable resolutions from Full to 1/32 step. There are four

phase drive outputs and two inhibit outputs for controlling 2-

phase bipolar or 4-phase unipolar motors. These outputs are

designed to drive two external H-bridge drivers for bipolar motor

windings or four external transistors for center-tapped unipolar

motor windings. These outputs can also be configured to drive

discrete external transistors for bipolar motor windings. A lookup

table sources the PWM duty cycle digital data for the two motor

windings corresponding to the step sequence. Two internal

DACs convert the PWM data to analog voltages as percentages

of the reference voltage applied at the Vref input. Currents

through the motor windings are monitored at the SENSE inputs

as voltage drops across fractional-Ohm resistors in series with

the H-bridge drivers. Upon turning on a PWM drive, when the

voltage at the SENSE input reaches the DAC reference level, the

PWM output is switched off for remainder of the cycle. The PWM

cycle is fixed at Tpwm = 256/fc, where fc is the clock frequency

at the XTLI input. The PWM cycles for the two drives are started

simultaneously but terminated separately per individual DAC

references.

An input is provided for the holding torque state at lower winding

current in the motor idle state. The holding-torque current level is

adjusted with a separate reference voltage applied at the Vrefh

input. The Vrefh is automatically switched in if the motor idles for

a programmable specified delay following a micro-step.

PWM chopping can be applied either to the PHASE or to the

INHIBIT outputs. The chopping mode affects the manner in

which the winding current decays during a PWM cycle.

There are four selectable decay modes: Fast-decay, Slow-

decay, Single-mixed-decay and Dual-mixed-decay.

In the Fast-decay mode the diagonal high side and low side

transistors of the H-bridge are both turned off during the PWM off

period. This causes the inductive current to be dissipated

through the bypass diodes in a direction opposing the motor

supply voltage resulting in fast decay.

In the Slow-decay mode the low side transistor of the H-bridge is

turned off keeping the high side transistor on during the PWM off

period. This causes the inductive current to re-circulate through

the high side transistor and diode loop. The current decays

slowly because of the low loop voltage. The Slow-decay can be

useful for motors that do not store enough energy in the windings

leading to an average current too low for any useful torque.

In the Single-mixed-decay mode, slow and fast decays are

combined in the following way:

♦

When the motor is idle, slow decay is applied to both windings

to guarantee lowest current ripple in a holding state.

♦

When the motor is stepping, if the step requires the current in a

winding to decrease, fast decay is applied to the winding for a

programmable duration followed by slow decay. If the step

requires the current in a winding to increase, slow decay is

applied to the winding.

In Dual-mixed-decay mode, mixed decay is applied to both

windings for every step with fast decay being followed by slow

decay.

LSI/CSI

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

LS8292

LS8293

8292-061413-1