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 FUNCTION S - L297/1 - L297D (continued)
CIRCUIT OPERATI ON
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-
ceiv es step c loc k , direction and m ode signals from
the systems controller (usually a microcomputer
chip) and generates c ontrol signals for the power
stage.
The principal functions are a translator , whic h gen-
erates the motor phase sequences, and a dual
PWM chopper circuit which regulates the current in
the motor windings. The translator generates three
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 b y
the L297 in half step and wa ve drive modes. These
signals, which connect directly to the L298’s enable
inputs, are intended to s peed c ur rent dec ay 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 CONTR OL 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 eac h pair
(AB or CD) is activated (rather than interrupting the
line then active). In L297 + L298 configurations this
technique reduces dissipation in the load current
sense resistors.
A common on-chip oscillator drives the dual chop-
per . It supplies pulses at the chopper rate which set
the two flip-flops FF 1 and FF2. When t he current in
a winding r eaches the pr ogrammed peak v alue the
voltage across the sense resistor (connected to
one of t he s ense inputs S ENS1 or SENS2) equals
Vref and the corresponding comparator resets its
flip flop, interrupting the drive current until the nex t
oscillator pulse arrives. The peak current for both
windings is programmed by a voltage divider on the
Vref input.
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
Rth-j-amb Thermal resistance junction-ambient max 80 100 °C/W
THERMAL D ATA
4/11
L297