LS7290 Datasheet, PDF (1/9 Pages) LSI Computer Systems – STEPPER MOTOR CONTROLLER

LS7290
STEPPER MOTOR CONTROLLER
July 2011
FEATURES:
• Controls Bipolar and Unipolar motors
• Cost-effective replacement for L297
• Full, ½ step mode selected with mode input
• Direction control
• Reset input
• Step control input
• Enable input
• PWM chopper circuit for current control
• Two peak-current comparators with external reference input
• Step control frequency and duty cycle controlled by an external frequency source
or by an internal crystal controlled oscillator (typically 8 MHz)
• All inputs and outputs TTL/CMOS compatible (TTL for 5V operation)
• 3V to 5.5V Operation (VDD – VSS)
• LS7290 (DIP), LS7290-S (SOIC), LS7290-TS (TSSOP) – See Figure 1.
PIN ASSIGNMENT
TOP VIEW
DESCRIPTION:
The LS7290 generates Phase Drive outputs and PWM outputs for controlling two-
phase Bipolar Motors or four-phase Unipolar Motors, respectively. The LS7290
contains a mode controlled look-up table for generating the motor duty cycle drive
sequences. There are four outputs which 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 (Refer to Table 2). The LS7290 can step a
motor in full steps and half steps. The refresh rate is set using an internal oscillator
controlled by a crystal or by use of an external input clock. Typical refresh rate is equal
to 31.25kHz with the clock frequency set at 8MHz. Peak-current feedback control using
pulse-width modulation is used in full-step or half-step modes. The chopper consists of
a voltage comparator, flip-flop and external sense resistor. The internal oscillator sets
the flip-flop and enables the INH1 and INH2 outputs at the beginning of each PWM
cycle. Once the peak motor current causes the voltage across the sense resistors to
reach the voltage set by VREF, the outputs are disabled until the next oscillator pulse.
The VREF voltage sets the peak current in each motor winding.
INPUT/OUTPUT DESCRIPTION
RESET Input
Active low. Resets the PWM table pointer to HOME position per Table 2 and brings
INH1 and INH2 low. Upon power-up, a POR circuit also resets the PWM table pointer.
ENABLE Input
Active low. When high (inactive), brings PHA, PHB, PHC, PHD, INH1 and INH2 outputs
low.
STEP Input
Active low. A low-going pulse on this input causes the motor to advance one step.
FIGURE 1.
NOTE: Pins 2 and 3 are used for factory test
and must be tied to ground.
FRD/RVRS Input
A low input causes the motor to move in
incremental steps in reverse direction per Table 2.
A high input causes the motor to move in
incremental steps in forward direction per Table 2.
Switching directions can occur at any time.
MODE Input
Defines the stepping modes as follows:
MODE
full step mode
0
½ step mode
1
Stepping mode can be changed at any time.
SENSE1 / SENSE2 Inputs
Inputs for motor winding current sense. A
fractional-Ohm resistor connected in series with
each of the H-Bridge drivers produce SENSE1 and
SENSE2 voltages. These voltages are compared
with VREF voltage input, for generating the PWM
inhibit outputs.
7290-072011-1