AN379 - STMicroelectronics

APPLICATION NOTE

USING THE L6204, A BIPOLAR STEPPER AND

DC MOTOR DRIVER IN BCD TECHNOLOGY

by E Balboni

The L6204 is a DMOS dual full bridge driver

mainly designed to drive bipolar stepper motors.

All the inputs are TTL/CMOS compatible and

each bridge can be enabled by its own dedicated

input. The windings current can be regulated by

sensing the voltage drop across two low value re-

sistors at the low end of both the bridge: this is

the feedback for the current controller. To feed

thegatesof theupperDMOS, a peakto peak recti-

fier charges a capacitor in series with the Power

Supplyvoltage at the optimum DC leveldefined by

an on-board square wave oscillator. The L6204 ,

with 0.5 A drivecapability without externalheatsink

up to 70°C, is packaged in a 20 leads PowerDip

with four heattransfer pins.The Block diagram of

thedevice is shownin fig.1.

AN379/0690

Figure1: Block diagram of the L6204 single chip dual full bridge driver.

Containingtwo H-bridge drivers,the L6204 is a compact and simple solutionfor drivingtwo-phase bi-

polar stepper motors and in applicationswhere two DC motors must be driven.

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This is achieved by the configuration shown in

fig.3A. The two independent motors (A and B)

can be controlled by only one controller (L6506).

The sensing resistor (RsA, RsB) generatesa volt-

age proportional to the motor current, that is the

feedback for the current control loop. A second

loop, not shown in figure, can control the speed

stability while the direction is defined by the Input

state of the L6506. The Enable Input (ENA, ENB)

caninhibit one motor or the otherwhile the Power

Enable acts on both at the same time. D1 and D2

(BAT41 or equivalent), C3 and C4, generates the

bootstrap voltage by rectifiing the wave available

at pin. 11 of the L6204. When more than one

driver is used at the same Supply Voltage on a

common Printed Circuit Board, the bootstrap volt-

age can be generatedonly by one of them (mas-

ter) and used to supply all the other L6204

(slaves) saving diodes and capacitors. R1 C1 (R2

C2) is a snubber network that must be closely

connected to the output pins and its use is recom-

mended in all the application circuits using the

L6204. The values can be calculatedas it follows:

R = Vs/Ip and C = Ip/(dV/dt), where Vs is the

maximum Supply Voltage of the Application,Ip is

the peak of the load current and dV/dt is the Slew

Rate accepted as the optimum compromise be-

tween speed and transient generation/radiation

(SR of 200 V/µS are commonly chosen). The net-

work R5C5 sets the operating frequency accord-

ing to f = 1/(0.69 R5C5) for R5 ≥10Kohm. R3

and R4 are used to protect the comparator input

inside the L6506 against possible negative transi-

tions acrossthe sensingresistor RsA or RsB. The

L6204can be used with paralleled inputs and out-

puts to double the current capability of the single

bridge; for an optimized solution, however, 1.6

times the nominal current is recommended in-

GENERAL APPLICATIONS HINTS

The L6204 can be used in a very wide range of

applications such as the drive of lamps, sole-

noids, DC motors or any other inductive loads.

The drive of different loads in single-ended con-

figuration is shown in fig.2. The current in the

Load Z1, that may be a DC motor, can flow in

both the directions but its peak amplitude cannot

be controlled. By means of a change of the Duty

Cycle of the input signal it is possible to vary in

Open Loop Mode the steady state speed of the

DC motor: this is possible because the average

current in the winding is dependent from the Duty

Cycle. The L/R ratio must be a few times shorter

than the minimum DC. In a similar way it can be

dimmed a lampconnected to the supply(Z2) or to

ground (Z3). Very often, when a DC motor is

driven, peak current and speed must be booth

controlled in a Closed Loop Mode.

Figure2: TheL6204 is notintended onlyfor Bipolar Stepper applications:hereabove three different driver

configurationsare shown. Z1 is a DC motor to be drivenin bothCW andCCW direction.Z2 can

be solenoidlike a relayor hammer. Z3 canbe an alogenlamp whichlight intensity iscontrolled

by variable Duty Cycle.

APPLICATION NOTE

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stead of two. This configuration is shown in fig.2

to drive the load Z1. A more complex circuit, in

wich one paralleled L6204 drives a DC motor, is

shown in fig.3B; in this example the two chopper

of the L6506 are used to implement two func-

tions: 1) Current Control during speed variation

at Ip max = 0.8A and 2) Current Control during

brake and/or direction change at higher current

level that depends from the brake repetition (it

must be in the Max Ratings limit). The divider

R6R7 defines the brake current intensity as

V17/Rs while the product (Ip max.) x ( Rs) is the

limit of the reference voltage V16 for speed con-

trol. The Enable function is driven via the L6506 .

Since during the brake time the Enable of the

L6506 is chopped, the motor current ricirculates

via the Supply; because of this a suitable large

capacitor must be connectedin parallelto C2.

Figure3A: Bidirectional DC motor drive. TheL6204 can drive two motors.

APPLICATION NOTE

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Stepping Motor Driving

The drive of one stepping motor is shown in fig.4,

where the controller L297 generates the re-

quested signals to drive the motor in Half-Step

Mode or in Full Step Mode.

The rotation speed or step change is controlled

by a clock signal or a single clock pulse at pin.18

(CK). The Mode dependsfrom the logical state of

the H / F input while the state of the CW/CCWin-

put defines the direction of the rotation. Depend-

ing on the numbered state, odd or even, of an in-

ternal clock pulse at the moment at wich the

Full-Step Mode is selected, the motor is driven

with two-phases-on or with one-phase-onrespec-

tively. An open collector output (home) indicates

the translator state 0101 that occurs only during

an odd numberedstate of the internalclock.

Figure3B: BidirectionalDC motor drive. The L6204 candrive the motor in a paralleled configurationwhile

the L6506 provides the peak current control both during normal rotation and during braking

time.

APPLICATION NOTE

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This last is obtained from the oscillator the fre-

quency of which is fixed by the ratio 1/0.69 R5C5

about (R5 ≥10Kohm). The peak of the chopped

current is given by the ratio of the reference volt-

age at pin.15 and the value of the sensing resis-

tors Rs. When the four phase signals needed at

the inputs of the L6204 are generated in any

other way than by the L297 (for example, via

µProcessor), the motor driver needs one interface

to control the peak current. One possible solution

isshown in fig.5.

Figure4: Bipolar steppingmotor drive: phase sequencegenerationand current peakcontrol areachieved

by means of the controllerL297.

APPLICATION NOTE

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The motor can be driven in the Full-Step or in

Half-Step Mode. The chopped current Ip is con-

trolled at the value Vref/Rs where Vref is the out-

put voltage of the divider R6 R7. The pins 16

and 17 (reference input voltage of the controller)

can be driven with two different signals. This ar-

rangementallows to keep constantthe motor cur-

rent and the torque during the Half-Step Mode

revolutionof the stepper.This behavior is well ex-

plainedby the fig. 6.

Figure 5: The L6506can be used to control the peakcurrent in the windings of a bipolar stepper motor.

The poweris suppliedby the L6204.

APPLICATION NOTE

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Figure6: Characteristicsof theHalf -Step Modedrive with constanttorque control. Itshouldbe noted that

the resultant current is constant while the current in the windings alternates between

one-phase-onand two-phase-onwith a ratio of √2.

APPLICATION NOTE

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APPLICATION NOTE

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