N

°

NAME

FUNCTION

19

HALF/FULL

Half/full step select input. When high selects half step operation,

when low selects full step operation. One-phase-on full step mode

is obtained by selecting FULL when the L297’s translator is at an

even-numbered state.

Two-phase-on full step mode is set by selecting FULL when the

translator is at an odd numbered position. (The home position is

designate state 1).

20

RESET

Reset input. An active low pulse on this input restores the

translator to the home position (state 1, ABCD = 0101).

PIN FUNCTIONS - L297/L297D (continued)

CIRCUIT OPERATION

The L297 is intended for use with a dual bridge

driver, quad darlington array or discrete power

devices in step motor driving applications. It re-

ceives step clock, direction and mode signals from

the systems controller (usually a microcomputer

chip) and generates control signals for the power

stage.

The principal functions are a translator, which gen-

erates the motor phase sequences, and a dual

PWM chopper circuit which regulates the current in

the motor windings.The translator generatesthree

different sequences, selected by the HALF/FULL

input. These are normal (two phases energised),

wave drive (one phase energised) and half-step

(alternately one phase energised/two phases en-

ergised). Two inhibit signals are also generated by

the L297 in half step and wave drive modes. These

signals, which connect directly to the L298’senable

inputs, are intended to speed current decay when

a winding is de-energised. When the L297 is used

to drive a unipolar motor the chopper acts on these

lines.

An input called CONTROL determines whether the

chopper will act on the phase lines ABCD or the

inhibit lines INH1 and INH2. When the phase lines

are chopped the non-active phase line of each pair

(AB or CD) is activated (rather than interrupting the

line then active).In L297 + L298 configurationsthis

technique reduces dissipation in the load current

sense resistors.

A common on-chip oscillator drives the dual chop-

per.It suppliespulses at the chopper rate which set

the two flip-flops FF1 and FF2. When the current in

a winding reaches the programmed peak value the

voltage across the sense resistor (connected to

flip flop, interrupting the drive current until the next

oscillator pulse arrives. The peak current for both

windingsis programmedby a voltage divideron the

Ground noise problems in multiple configurations

can be avoided by synchronising the chopper os-

cillators. This is done by connecting all the SYNC

pins together, mounting the oscillator RC network

on one device only and grounding the OSC pin on

all other devices.

Symbol

Parameter

DIP20

SO20

Unit

Thermal resistance junction-ambient

max

80

100

°C/W

THERMAL DATA

4/11

L297-L297D