L292H [STMICROELECTRONICS]

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型号：	L292H
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L292

SWITCH-MODE DRIVER FOR DC MOTORS

DRIVING CAPABILITY : 2 A, 36 V, 30 KHz

2 LOGIC CHIP ENABLE

EXTERNAL LOOP GAIN ADJUSTEMENT

SINGLE POWER SUPPLY (18 TO 36 V)

INPUT SIGNAL SYMMETRIC TO GROUND

THERMAL PROTECTION

Multiwatt 15

DESCRIPTION

The L292 is a monolithic LSI circuit in 15-lead

Multiwatt ® package. It isintendedfor use, together

with L290 and L291, as a complete 3-chip motor

positioning system for applications such as car-

riage/daisy-wheel position control in type-writes.

ORDER CODE : L292

The L290/1/2 system can be directly controlled by

a microprocessor.

ABSOLUTE MAXIMUM RATINGS

Symbol

V_s

Parameter

Value

Unit

Power Supply

Input Voltage

Inhibit Voltage

Output Current

V_i

- 15 to + Vs

0 to Vs

2.5

V_inhibit

I_o

P_tot

°C

Total Power Dissipation (T_case= 75 °C)

T_stg

Storage and Junction Temperature

- 40 to + 150

TRUTH TABLE

Vinhibit

CONNECTION DIAGRAM (top view)

Output Stage

Condition

Pin 12

Pin 13

Disabled

Normal Operation

Disabled

March 1993

1/12

L292

THERMAL DATA

Symbol

Parameter

Value

Unit

Rth-j-case

Thermal resistance junction-case

Max

°C/W

ELECTRICAL CHARACTERISTICS (V_s= 36 V, T_amb= 25 °C, f_osc= 20 KHz unless otherwise specified)

Symbol

V_s

Parameter

Supply Voltage

Test conditions

Min.

Typ.

Max.

Unit

I_d

Quiescent Drain Current

Input Offset Voltage (pin 6)

Inhibit Low Level (pin 12, 13)

Inhibit High Level (pin 12, 13)

Low Voltage Condition

V_s= 20 V (offset null)

V_os

I_o= 0

±350

V_inh

3.2

I_inh

V_inh(L) = 0.4 V

V_inh(H) = 3.2 V

- 100

µA

High Voltage Conditions

Input Current (pin 6)

I_i

V_l= -8.8 V

V_l= +8.8 V

-1.8

0.5

V_i

Input Voltage (pin 6)

I_o= 2A

9.1

R_s1= R_s2= 0.2Ω

I_o= -2A

-9.1

I_o

Output Current

V_l= ± 9.8 V R_s1= R_s2= 0.2 Ω

± 2

V_D

Total Drop Out Voltage

(inluding sensing I_o= 2 A

resistors)

I_o= 1 A

3.5

0.44

235

Sensing Rsistor Voltage

Drop

V_RS

I_o= 2 A

T_j= 150°C

Transconductance

205

220

120

mA/V

KHz

I_o

R_s1= R_s2=0.2Ω

V_i

_s1= R_s2= 0.4Ω

f_osc

Frequency Range (pin 10)

BLOCK DIAGRAM AND TEST CIRCUIT

2/12

L292

SYSTEM DESCRIPTION

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 "de-

tenting".

The L290, L291 and L292 are intended to be used

as a 3-chip microprocessor controlled positioning

system. The device may be used separately - par-

ticularly the L292 motor driver - but since they will

usually be used together, a description of a typical

L290/1/2 system follows.

The mechanical/electrical interface consists of an

Figure 1. System Block Diagram

The system operates in two modes to achieve high

speed, high-accurancy positioning.

optical encoder which generates two sinusoidal

signals 90° out of phase (leading according to the

motordirection)andproportional infrequencyto the

speedofrotation. Theopticalencoderalsoprovides

an output at one position on the disk which is used

to set the initial position.

The opto encoder signals, FTAand FTB are filtered

by the networks R₂C₂and R₃C₃(referring to Fig.4)

andaresuppliedto theFTA/FTB inputs ontheL290.

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 the microprocessor

orders it to a new positio, the system operates

initially in an open-loop configuration as there is no

feedback from the tachometer generator. A maxi-

mum speed is reached, the tachometer chip output

backs off the processor signal thus reducing accel-

ering torque. The motor continues to run at rop

speed but under closed-loop control.

The main function on the L290 is to implement the

following expression:

dV_AB

dV_AA

FTA

| FTA |

FTB

| FTB |

Output signal (TACHO) =

•

−

•

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 A₁and A₂to obtain V_AAand V_AB

(typ.7 V_p). From V_AAand V_ABthe external differen-

tiatiorRC networks R₅C₆andR₄C₄givethesignals

V_MAand V_MBwhich are fed to the multipliers.

As the target position is approached, themicroproc-

essor lowers the value of the speed-demand word;

this reduces the voltage at the main summing point,

in effect braking the motor. The braking is applied

progressively until the motor is running at minimum

speed.

3/12

L292

external RC network (R₂₀, C₁₇- pins 11 and 10)

where:

The second input to each multipler consists of the

sign of the first input of the other multiplier before

differentiation, these areobtained using thecompa-

rators C_s1and C_s2. The multiplier outputs, C_SAand

C_SB, are summed by A₃to give the final output

signal TACHO. The peak-topeak ripple signal of the

TACHOcanbefoundfromthefollowingexpression:

2RC

1 f_osc

(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).

V_{ripple p − p}

( √ 2 − 1 ) • V_{thaco DC}

The max value of TACHO is:

V_{tacho max}

√ 2 • V_thaco

Using the coparatorsC₁and C₂another two signals

fromV_AAand V_ABarederived - thelogicsignalsSTA

and STB.

The errorsignalobtained by the addition oftheinput

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.

This signals are used by the microprocessor to

determine the position by counting the pulses.

The L2910internalreferencevoltageisalsoderived

from V_AAand V_AB:

V_ref= | V_AA| + | V_AB

The interval between one side of the bridge switch-

ing off and the other switching on, τ, is programmed

by C₁₇in conjuction with an internal resistor Rτ.

This can be foud from:

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.

τ = Rτ • C_pin

(C₁₇in thediagram)

10.

The TACHO signal and V_refare sent to the L291 via

filter networks R₈C₈R₉and R₆C₇R₇respectively.

Pin 12 of this chip is the main summing point of the

system where TACHO and the D/Aconverter output

are compared.

Since Rτ is approximately 1.5 KΩ and the recom-

mended τ to avoid simultaneous conduction is 2.5

µs C_{pin 10}should be around 1.5 nF.

The current sense resistors R₁₈and R₁₉should be

high precision types (maximum tolerance ± 2 %)

and the recommended value is given by:

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- iscomparedwiththeTACHOsignaland

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.

R_max• I_o

≤ 0.44 V

max

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

This same reference voltage supplies the triangle

wave oscillator whose frequency is fixed by the

4/12

L292

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).

The enable inputs were implemented in this way

because they are intended to be driven directly by

a microprocessor. Currently available microproces-

sors may generates spikes as high as 1.5 V during

Figure 3.

Figure 2.

Figure 4 . Application Circuit.

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_S1= R_S2= R_S(sensing resistors)

= 2.5 • 10^-3Ω (current sensing amplifier transconductance)

R₄

L_M= Motor inductance, R_M= Motor resistance, I_M= Motor current

I_M

G_mo

6/12

(DC transfer function from the input of the comparator (V_TH) to the motor

current (I_M)).

s = 0

L292

Neglecting the VCEsat of the bridge transistors and the VBE of the diodes:

2 V_s

V_R

G_mo

where

: V_S= supply voltage

(1)

R_M

V_R= 8 V (reference voltage)

DC TRANSFER FUNCTION

In order to be sure that the current loop is stable the following condition is imposed :

L_M

1 + sRC = 1 + s

(pole cancellation)

(2)

R_M

L_M

from which RC =

(Note that in practice R must greater than 5.6 KΩ)

R_M

The transfer function is then,

I_M

V_I

R₂R₄

R₁R₃

1 + s R_FC_F

G_moR_s+ s R₄C + s²R_FC_FR₄C

(s) =

G_mo

(3)

In DC condition, this is reduced to

I_M

V_I

R₂R₄

R₁R₃

R_s

0.044

R_s

(o) =

•

[

]

(4)

(5)

OPEN-LOOP GAIN AND STABILITY CRITERION

For RC = L_M/ R_M, the open loop gain is:

R_s

R₄

R_F

G_moR_s

R₄

Aβ =

• G_mo

sR subF C

1 + s R_FC_F

(1 + s R_FC_F)

In order to achieve good stability, the phase margin must be greater than 45° when | Aβ | = 1.

That means that, at f_F=

must be | Aβ | < 1 (see fig. 7), that is :

2 π R_FC_F

G_moR_sR_FC_F

| Aβ | f =

< 1

(6)

2 π R_FC_F

R₄C

√

Figure 7. Open Loop Frequency Response

7/12

L292

CLOSED-LOOP SYSTEM STEP RESPONSE

Figure 8. Small Signal Step Response

(normalized amplitude vs.

t / R_FC_F).

a) Small - signals analysis.

The transfer function (3) can be written as follows:

1 +

2 ξ ω o

I_M

V_I

0.044

R_s

(s) =

(7)

2 ξs + s²

1 +

ω_o

√G_moR_s

where wo =

is the cutoff frequency

is the dumping factor

R₄C R C

√

R₄C

4 R C_FG_moR_s

ξ =

By choosing the ξ value, it is possible to determine

the system response to an input step signal.

Examples :

V₇= 200 mV/div.

I_M= 100 mA/div.

t = 100 µs/div.

1) ξ = 1 from which

with V_I= 1.5 Vp.

−

0.044

R_s

2R_FC_F

I_M(t) =

[ 1 − e

(1 +

) ] • V_i

4 R_FC_F

(where Vi is the amplitude of the input step).

2) ξ =

from which

√

0.044

R_s

−

2 R_FC_F

) V_i

I_M(t) =

(1 − cos

2 R_FC_F

8/12

L292

It ispossibleto verify thattheL292works in"closed-

loop" 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

V_R, present at the non-inverting input of the same

amplifier.

The previous linear analysis is correct for this ex-

ample.

Descresing the ξ value, the rise-time of the current

decreases. But foragoodstability, fromrelationship

(6), the maximum value of ξ is:

ξmin =

(phase margin = 45°)

2 ⁴√ 2

b) Large signal reponse

The large step signal response is limited by slew-

rate and inductive load.

In this case, during the rise-time of the motor

current, The L292 works is open-loop condition.

CLOSED LOOP SYSTEM BANDWIDTH.

A good choice for x is the value 1 / √2. In this case :

I_M

V_I

1 + s R_FC_F

(8)

0.044

R_s

(s) =

1 + 2s R_FC_F+ 2s R_F²C_F

The module of the transfer function is :

√1 + ω²R_F

(9)

I_M

V_I

0.044

R_s

| =

[ ( 1 + 2 ω R_FC_F) ²+ 1 ] • [ ( 1 − 2 ω R_FC_F) ²+ 1 ]

√

I_M

V_I

0.044

The cutoff frequency is derived by the expression (9) by putting |

which :

| = 0.707 •

(−3 dB), from

0.9

R C

0.9

2π R_FC_F

ω_T

f _T=

9/12

L292

Example :

a) Data

- Motors characteristics:

LM = 5 mH

RM = 5 W

L_M/ R_M= 1msec

- Voltage and current characteristics:

V_s= 20 V

I_M= 2 A

V_I= 9.1 V

- Closed loop bandwidth : 3 kHz

b) Calculation

- From relationship (4) :

0.044

R_s=

V_I= 0.2 Ω

I_M

and from (1) :

2V_S

R_MV_R

G_mo

= 1 Ω ⁻¹

- RC = 1 msec [from expression (2) ].

- Assuming ξ = 1/ √2 ; from (7) follows :

400 C

4R_FC_F• 0.2

ξ²

- The cutoff frequency is :

−3

143 ^•10

f _T

= 3 kHz

R_FC_F

c) Summarising

- RC = 1.10^-3sec

1000 C

R_FC_F

- R_FC_F47 µs

C = 47 nF

R = 22 KΩ

= 1

For R_F= 510 Ω → C_F= 92 nF

10/12

L292

MULTIWATT15 PACKAGE MECHANICAL DATA

inch

TYP.

DIM.

MIN.

TYP.

MAX.

MIN.

MAX.

0.197

0.104

0.063

2.65

1.6

0.039

0.49

0.66

1.02

17.53

19.6

0.55

0.75

0.019

0.026

0.040

0.690

0.772

0.022

0.030

0.060

0.710

1.27

1.52

0.050

0.700

17.78

18.03

20.2

22.5

18.1

17.75

10.9

2.9

0.795

0.886

0.713

0.699

0.429

0.114

0.191

0.218

0.102

0.152

21.9

21.7

17.65

17.25

10.3

2.65

4.25

4.63

1.9

22.2

22.1

0.862

0.854

0.695

0.679

0.406

0.104

0.167

0.182

0.075

0.144

0.874

0.870

17.5

10.7

0.689

0.421

4.55

5.08

4.85

5.53

2.6

0.179

0.200

Dia1

1.9

2.6

3.65

3.85

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 implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned

in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.

SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express

written approval of SGS-THOMSON Microelectronics.

SGS-THOMSON Microelectronics GROUP OF COMPANIES

Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore -

Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A.

12/12

L292H [STMICROELECTRONICS]

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