LSI/CSI
PRELIMINARY
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
LS8292
LS8293
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405
MICRO-STEPPING MOTOR CONTROLLER
June 2013
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.
8292-061413-1
LSI [ LSI COMPUTER SYSTEMS ]
