L292(1993) Ver la hoja de datos (PDF) - STMicroelectronics
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L292 Datasheet PDF : 12 Pages
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L292
The second input to each multipler consists of the
sign of the first input of the other multiplier before
differentiation, these are obtained using the compa-
rators Cs1 and Cs2. The multiplier outputs, CSA and
CSB, are summed by A3 to give the final output
signal TACHO. The peak-topeak ripple signal of the
TACHO can be found from the following expression:
Vripple p − p
=
π
4
(√2
−
1)
•
Vthaco DC
The max value of TACHO is:
Vtacho max
=
π
4
√ 2 • Vthaco DC
Using the coparators C1 and C2 another two signals
from VAA and VAB are derived - the logic signals STA
and STB.
This signals are used by the microprocessor to
determine the position by counting the pulses.
The L2910 internal reference voltage is also derived
from VAA and VAB:
Vref = | VAA | + | VAB |
This reference is used by the D/A converter in the
L291 to compensate for variations in input levels,
temperature changes and ageing.
The "one pulse per rotation" opto encoder output
is connected to pin 12 of the L290 (FTF) where it is
squared to give the STF logic output for the micro-
processor.
The TACHO signal and Vref are sent to the L291 via
filter networks R8 C8 R9 and R6 C7 R7 respectively.
Pin 12 of this chip is the main summing point of the
system where TACHO and the D/A converter output
are compared.
The input to D/A converter consists of 5 bit word
plus a sign bit supplied by the microprocessor. The
sign bit represets the direction of motor rotation.
The (analogue) output of the D/A conveter -
DAC/OUT - is compared with the TACHO signal and
the risulting error signal is amplified by the error
amplifier, and subsequently appears on pin 1.
The ERRV sognal (from pin 1 , L291) is fed to pin
6 of the final chip, the L292 H-bridge motor-driver.
This input signals is bidirectional so it must be
converted to a positive signal bacause the L292
uses a single supply voltage. This is accomplished
by the first stage - the level shifter, which uses an
internally generated 8 V reference.
This same reference voltage supplies the triangle
wave oscillator whose frequency is fixed by the
external RC network (R20, C17 - pins 11 and 10)
where:
1 fosc =
1
2RC
(with R ≥ 8.2 K Ω)
The oscillator determines the switching frequency
of the output stage and should be in the range 1 to
30 KHz.
Motor current is regulated by an internal loop in the
L292 which is performed by the resistors R18, R19
and the differential current sense amplifier, the out-
put of which is filtered by an external RC network
and fed back to the error amplifier.
The choise of the external components in these RC
network (pins 5, 7, 9) is determined by the motor
type and the bandwidth requirements. The values
shown in the diagram are for a 5Ω, 5 MH motor.
(See L292 Transfer Function Calculation in Appli-
cation Information).
The error signal obtained by the addition of the input
and the current feedback signals (pin 7) is used to
pulse width modulate the oscillator signal by means
of the comparator. The pulse width modulated sig-
nal controls the duty cycle of the Hbridge to give an
output current corresponding to the L292 input
signal.
The interval between one side of the bridge switch-
ing off and the other switching on, τ, is programmed
by C17 in conjuction with an internal resistor Rτ.
This can be foud from:
τ = Rτ • Cpin 10. (C17 in the diagram)
Since Rτ is approximately 1.5 KΩ and the recom-
mended τ to avoid simultaneous conduction is 2.5
µs Cpin 10 should be around 1.5 nF.
The current sense resistors R18 and R19 should be
high precision types (maximum tolerance ± 2 %)
and the recommended value is given by:
Rmax • Io max ≤ 0.44 V
It is possible to synchronize two L292 ’s, if desired,
using the network shown in fig. 2.
Finally, two enable inputs are provited on the L292
(pins 12 and 13-active low and high respectively).
Thus the output stage may be inhibited by taking
pin 12 high or by taking pin 13 low. The output will
also be inhibited if the supply voltage falls below 18
V.
4/12
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