SGS Thomson Microelectronics L292 Datasheet

SWITCH-MODE DRIVER FOR DC M OTORS

DRIVING CAPABILITY : 2 A, 36 V , 30 KHz
2 LOGIC CHIP ENABLE
EXTERNAL L OOP GA IN ADJUSTEME NT
SINGLE PO WE R SUP P LY (18 T O 36 V)
INPUT SIGNAL SYMMETRIC TO GROUND
THERMAL PROTECTION

DESCRIPTION

The L292 is a monolithic LSI circuit in 15-lead
Multiwatt ® package. It is intended for use, together
with L290 and L291, as a complete 3-chip motor
positioning system for applications such as car­riage/daisy-wheel position control in type-writes.

The L290/1/2 system can be directly controlled by
a microprocessor.

L292

Multiwatt 15

ORDER CODE : L292

ABSOLUT E MAX IMUM R ATI NGS

Symbol Parameter Value Unit

V

s

V

i

V

inhibit

I

o

P

tot

T

stg

TRUTH TABLE

Pin 12 Pin 13

L L Disabled

L H Normal Operation

Power Supply 36 V
Input Voltage - 15 to + Vs V
Inhibit Voltage 0 to Vs V
Output Current 2.5 A
Total Power Dissipation (T
Storage and Junction Temperature - 40 to + 150

= 75 °C)

case

25 W

CONNECT ION DI AG RAM (top view)

Vinhibit

Output Stage

Condition

°C

H L Disabled

H H Disabled

March 1993

1/12

L292

THERMAL DATA

Symbol Parameter Value Unit

Rth-j-case Thermal resistance junction-case Max 3

°C/W

ELECTRICAL CHARACTERISTICS (Vs = 36 V, T

= 25 °C, f

amb

= 20 KHz unless otherwise specified)

osc

Symbol Parameter Test conditions Min. Typ. Max. Unit

Supply Voltage 18 36 V

V

s

I

Quiescent Drain Current Vs = 20 V (offset null) 30 50 mA

d

Input Offset Voltage (pin 6) Io = 0

V

os

Inhibit Low Level (pin 12, 13) 2 V

V

inh

±350

mV

Inhibit High Level (pin 12, 13) 3.2 V

Low Voltage Condition V

I

inh

High Voltage Conditions V

Input Current (pin 6) Vl = -8.8 V

I

i

Input Voltage (pin 6)

V

i

I

Output Current

I

o

V

Total Drop Out Voltage (inluding sensing

D

I

Sensing Rsistor Voltage

V

RS

Drop
Transconductance

I

o

V

i

f

Frequency Range (pin 10) 1 30 KHz

osc

(L) = 0.4 V - 100

inh

(H) = 3.2 V 10

inh

= +8.8 V

V

l

= Rs2 = 0.2Ω

R

s1

= ± 9.8 V Rs1 = Rs2 = 0.2 Ω± 2

V

l

resistors)

T

= 150°C

j

= Rs2 =0.2Ω

R

s1

R

= Rs2 = 0.4Ω

s1

I

= 2A 9.1 V

o

= -2A -9.1 V

o

A

Io = 2 A

= 1 A 3.5 V

o

I

= 2 A 0.44 V

o

205 220 235 mA/V
120 mA/V

µA
µA

-1.8

0.5

mA
mA

5V

BLOCK DIAGRAM AND TEST CIRCU IT

2/12

SYSTEM DESCRIPTION

The L290, L291 and L292 are intended to be used
as a 3-chip microprocessor controlled positioning
system. The device may be used separately - par­ticularly the L292 motor driver - but since they will
usually be used together, a description of a typical
L290/1/2 system follows.

Figure 1. System Block Diagram

L292

At the time, the microprocessor orders a switch to
the position mode, (strobe signal at pin 8 of L291)
and within 3 to 4 ms the L292 drives the motor to
a null position, where it is held by electronic "de­tenting".

The mechanical/electrical interface consists of an

The system operates in two modes to achieve high
speed, high-accurancy positioning.

Speed commands for the system originate in the
microprocessor. It is continuosly updated on the
motor position by means of pulses from the L290
tachometer chip, whitch in tur gets its information
from the optical encoder. From this basic input, the
microprocessor computes a 5-bit control word that
sets the system speed dependent on the distance
to travel.

When the motor is stopped and t he microprocessor
orders it to a new positio, the system operates
initially in an open-loop configurat ion as there is n o
feedback from the tachometer generator. A maxi­mum speed is reached, the t achometer chip out put
backs off the processor signal thus reducing accel­ering torque. The motor continues to run at rop
speed but under closed-loop control.

As the target pos ition is approached, the microproc­essor lowers the v alue of the speed-dem and wor d;
this reduces the voltage at the main summing point,
in effect braking the motor. The braking is applied
progressively until t he motor is r unning at minimum
speed.

optical encoder which generates two sinusoidal
signals 90° out of phase (leading according to the
motor direction) and proportional in frequency to the
speed of rotation. The optical encoder also provides
an output at one position on the disk which is used
to set the initial position.

The opto encoder signals, FTA and FT B are filtered
by the networks R

and R3 C3 (referring to Fig.4)

2C2

and are supplied to the FT A/FTB inputs on the L290.
The main function on the L290 is to implement the

following expression:

Output signal (T ACHO) =

dV

FTA

AB

•

dt

| FTA |

−

dV

FTB

AA

•

dt

| FTB |

Thus the mean value of TACHO is proportional to
the rotation speed and its polarity indicates the
direction of rotation.

The above function is performed by amplifying the
input signals in A

and A2 to obtain VAA and V

1

AB

(typ.7 Vp). From VAA and VAB the external differen­tiatior RC networks R

and VMB which are fed to the multipliers.

V

MA

and R4 C4 give the signals

5 C6

3/12

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 comp a­rators C
C

SB

and Cs2. The multiplier outputs, CSA and

s1

, are summed by A3 to give the final output
signal T ACHO. The peak-topeak ripple signal of the
T ACHO can be found from the following express ion:

V

ripple p −

( √ 2 − 1 ) • V

p

4

thaco

DC

π

=

The max value of TACHO is:

V

tacho max

=

π

√ 2 • V

4

thaco DC

Using the coparators C1 and C2 another two signals
from V

and VAB are derived - the logic signals STA

AA

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 V

and VAB:

AA

= | VAA | + | VAB |

V

ref

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 micro­processor .
The T ACHO signal and V
filter networks R

8 C8 R9

are sent to the L291 via

ref

and R6 C7 R7 respectively.
Pin 12 of this chip is the main summing point of the
system where T ACHO 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 T ACHO 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 accom plished
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 (R

, C17 - pins 11 and 10)

20

where:

1 f

osc

=

1

(with R ≥ 8.2 K Ω)

2RC

The oscillator determines the switching frequency
of the output stage and should be in the range 1 to
30 KHz.
Motor current is r egulated by an internal loop in the
L292 which is performed by the resistors R

18

, R

19

and the differential curr ent sense amplifier, the out­put of which is filtered by an external RC network
and fed back to the error amplifier.
The choise of the extern al components in thes e 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 Appli­cation 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 sig­nal controls the duty cycle of the Hbr idge to give an
output current corresponding to the L292 input
signal.
The interval between one side of the bridge swit ch­ing off and the other switching on, τ, is programmed

in conjuction with an internal resistor Rτ.

by C

17

This can be foud from:

= R τ • C

τ

(C17 in the diagram)

pin 10.

Since Rτ is approximately 1.5 KΩ and the recom­mended τ to avoid simultaneous conduction is 2.5
µs C

The current sense r esis tors R

should be around 1.5 nF.

pin 10

and R19 should be

18

high precision types (maximum tolerance ± 2 %)
and the recommended value is given by:

• Io

R

max

≤ 0.44 V

max

It is possible to synchroniz e 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