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
L292
The enable inputs were implemented in this way
because they are intended to be driven directly by
a microprocessor . Currently available micropr ocessors may generates s pikes as high as 1.5 V during
Figure 2.
Figure 4 . Applic ation Circui t.
power-up. These inputs may be used for a variety
of applications such as motor inhibit during reset of
the logical system and power-on reset (see fig. 3).
Figure 3.
5/12
L292
APPLICATION INFORMATION
This section has been added in order to help the designer for the best choise of the values of external
components.
Figure 5. L292 Block Diagram.
The schematic diagram used for the Laplace analysis of the system is shown in fig. 6.
Figure 6.
R
= RS2 = RS (sensing resistors )
S1
1
= 2.5 • 10-3 Ω (current sensing amplifier transconductance)
R
4
= Motor inductance, RM = Motor resistance, IM = Motor current
L
M
Gmo =
current (I
IM
| s = 0 (DC transfer function from the input of the comparator (VTH) to the motor
)).
M
6/12
Neglecting the VCEsat of the bridge transistors and the VBE of the diodes:
2
=
1
G
mo
R
V
s
M
where : VS = supply voltage (1)
V
R
VR = 8 V (reference voltage)
DC TRANSFE R FU NCT ION
In order to be sure that the current loop is stable the following condition is imposed :
L
1 + sRC = 1 + s
from which RC =
M
(pole cancellation) (2)
R
M
L
M
(Note that in practice R must greater than 5.6 KΩ)
R
M
The transfer function is then,
L292
I
M
(s) =
V
I
R
R
2
R1 R
4
Gmo
3
Gmo Rs + s R4 C + s2 RF CF R4 C
1
+ s R
F CF
(3)
In DC condition, this is reduced to
R
I
M
(o) =
V
I
R
2
R1 R
4
3
•
0.044
1
=
R
R
s
A
[
s
] (4)
V
OPEN-LOOP GAIN AND STABILITY CRITERION
For RC = L
Aβ =
/ RM, the open loop gain is:
M
1
sR subF C
• G
mo
R
R
s
1 + s RF C
4
R
F
F
=
Gmo R
R
4
s
C
(1 + s R
s
1
(5)
C
)
F
F
In order to achieve good stability , the phase margin must be greater than 45° when | A β | = 1.
That means that, at f
| A β | f =
2 π R
1
F CF
=
F
=
2 π R
G
mo Rs
R
4
1
must be | A β | < 1 (see fig. 7), that is :
F CF
C
R
F
C
F
< 1 (6)
2
√
Figure 7. Open Loop Frequency Response
7/12
L292
CLOSED-LOOP SYSTEM STEP RESPONSE
a) Small - signals an alysi s.
The transfer function (3) can be written as follows :
I
M
(s) =
V
I
where wo =
√ R4 C
ξ =
4 R
0.044
√
R
CF Gmo R
F
R
s
G
mo
C RF C
4
1 +
1 +
R
s
is the cutoff frequency
F
is the dumping factor
s
By choosing the ξ value, it is possible to determine
the system response to an input step signal.
Examples :
1) ξ = 1 from which
I
M
(t) =
0.044
R
s
[ 1 − e −
2R
2 ξ
2 ξs + s
ωo ω
t
F CF
(1 +
s
ω o
o
4 R
2
t
F CF
2
(7)
) ] • V
Figure 8. Small Signal Step Response
(normalized amplitude vs.
t / R
= 200 mV/div.
V
7
= 100 mA/div.
I
M
FCF
).
t = 100 µs/div.
= 1.5 Vp.
with V
I
i
(where Vi is the amplitude of the input step).
1
2) ξ =
(t) =
I
M
from which
2
√
0.044
(1 − cos
R
s
2 R
t
F CF
e −
2 R
t
F CF
) V
i
8/12
L292
It is possible to verify that the L292 works in "closedloop" conditions during the entire motor current
rise-time: the voltage at pin 7 inverting input of the
error amplifier) is locked to the reference voltage
, present at the non-inverting input of the same
V
R
amplifier.
The previous linear analysis is correct for this example.
Descresing the ξ value, the rise- time of the current
decreases. But for a good stability , from relationship
(6), the maximum value of ξ is:
CLOSED LOOP SYSTEM BANDWIDTH.
A good choice for x is the value 1 / √2. In this case :
I
M
(s) =
V
I
0.044
R
s
1 + 2s RF CF + 2s 2 RF 2 CF
The module of the transfer function is :
I
|
V
M
| =
I
0.044
R
s
2
[ ( 1 + 2 ω RF CF ) 2 + 1 ] • [ ( 1 − 2 ω RF CF ) 2 + 1 ]
√
ξmin =
1
(phase margin = 45°)
4
2
√
2
b) Large sign al rep ons e
The large step signal response is limited by slewrate and inductive load.
In this case, during the rise-time of the motor
current, The L292 works is open-loop condition.
1
+ s R
√1 + ω
F CF
2
RF 2 CF
2
2
(8)
(9)
The cutoff frequency is derived by the expression (9) by putting |
which :
ω
T
=
0.9
f T =
R
F CF
2π
0.9
R
F CF
I
M
| = 0.707 •
V
I
0.044
(−3 dB), from
R
s
9/12
L292
Example :
a) Data - Motors characterist ics: LM = 5 mH
RM = 5 W
L
/ RM = 1msec
M
- Voltage and current char acter ist ics :
V
- Closed loop bandwidth : 3 kHz
b) Calculation - From relationship (4) :
and from (1) :
- RC = 1 msec [from expression (2) ].
- Assuming ξ = 1/ √2 ; from (7) follows :
= 20 V IM = 2 A VI = 9.1 V
s
0.044
=
R
s
G
=
mo
VI = 0.2 Ω
I
M
2V
S
RM V
R
= 1 Ω
−1
c) Summarising
1
2
ξ
=
=
2
- The cutoff frequency is :
143
f
=
T
- RC = 1.10
1000 C
-
R
F CF
- R
F CF
-3
sec
= 1
≅ 47 µs
4R
• 10
RF C
400 C
F CF
−3
F
• 0.2
= 3 kHz
C = 47 nF
R = 22 KΩ
For R
= 510 Ω → CF = 92 nF
F
10/12
MULTIW ATT15 P ACKA GE ME CHANI CAL DATA
DIM.
MIN. TYP. MAX. MIN. TYP. MAX.
A 5 0.197
B 2.65 0.104
C 1.6 0.063
D 1 0.039
E 0.49 0.55 0.019 0.022
F 0.66 0.75 0.026 0.030
G 1.02 1.27 1.52 0.040 0.050 0.060
G1 17.53 17.78 18.03 0.690 0.700 0.710
H1 19.6 0.772
H2 20.2 0.795
L 21.9 22.2 22.5 0.862 0.874 0.886
L1 21.7 22.1 22.5 0.854 0.870 0.886
L2 17.65 18.1 0.695 0.713
L3 17.25 17.5 17.75 0.679 0.689 0.699
L4 10.3 10.7 10.9 0.406 0.421 0.429
L7 2.65 2.9 0.104 0.114
M 4.25 4.55 4.85 0.167 0.179 0.191
M1 4.63 5.08 5.53 0.182 0.200 0.218
S 1.9 2.6 0.075 0.102
S1 1.9 2.6 0.075 0.102
Dia1 3.65 3.85 0.144 0.152
mm inch
L292
11/12
L292
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No
license is granted by implicat ion o r otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications menti oned
in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronics products are not a uthorized for use as critical components in life support devices or systems without ex press
written approval of SGS-THOMSON Microelectronics.
© 1994 SGS-THOMSON Microelectronics - All Rights Reserved
SGS-THOMSO N Microelec tronics G ROUP OF COMP ANI ES
Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore -
Spain - Sweden - Switzerland - T aiwan - Thaliand - United Kingdom - U.S.A.
12/12
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