7290-072011-1

FEATURES:

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Controls Bipolar and Unipolar motors

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Cost-effective replacement for L297

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Full, ½ step mode selected with mode input

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Direction control

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Reset input

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Step control input

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Enable input

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PWM chopper circuit for current control

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Two peak-current comparators with external reference input

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Step control frequency and duty cycle controlled by an external frequency source

or by an internal crystal controlled oscillator (typically 8 MHz)

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All inputs and outputs TTL/CMOS compatible (TTL for 5V operation)

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LS7290 (DIP), LS7290-S (SOIC), LS7290-TS (TSSOP) – See Figure 1.

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.

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.

STEPPER MOTOR CONTROLLER

July 2011

LS7290

PIN ASSIGNMENT

TOP VIEW

FIGURE 1.