PBL3772-1 Ver la hoja de datos (PDF) - Ericsson

Número de pieza

componentes Descripción

Fabricante

PBL3772-1

Dual Stepper Motor Driver

Ericsson  

PBL 3772/1

Functional Description

Each channel of the PBL 3772/1

consists of the following sections: an

output H-bridge with four transistors,

capable of driving up to 1000 mA

continuous current to the motor winding;

a logic section that controls the output

transistors; an S-R flip-flop; and a

comparator. The clock-oscillator is

common to both channels.

Constant current control is achieved

by switching the output current to the

windings. This is done by sensing the

peak current through the winding via a

current-sensing resistor RS, effectively

connected in series with the motor

winding during the turn-on period. As

the current increases, a voltage

develops across the sensing resistor,

which is fed back to the comparator. At

the predetermined level, defined by the

voltage at the reference input VR, the

comparator resets the flip-flop, which

turns off the output transistors. The

current decreases until the clock

oscillator triggers the flip-flop, which

turns on the output transistors again,

and the cycle is repeated.

The current paths during turn-on, turn-

off and phase shift are shown in figure 5.

Note that the upper recirculation diodes

are connected to the circuit externally.

Applications Information

Current control

The output current to the motor winding

is determined by the voltage at the

reference input and the sensing resistor,

RS.

Chopping frequency, winding induct-

ance and supply voltage also affect the

current, but to much less extent.

The peak current through the sensing

resistor (and motor winding) can be

expressed as:

I = 0.18 • ( V / R ) [A]

M,peak

R

S

i.e., with a recommended value of

0.47 ohm for the sensing resistor RS, a

2.5 V reference voltage will produce an

output current of approximately 960 mA.

To improve noise immunity on the V

R

input, the control range may be

increased to 5 V if R is correspondingly

S

changed to 1 ohm.

External components

The PBL 3772/1 exhibits substantially

less power dissipation than most other

comparable stepper motor driver ICs on

the market. This has been achieved by

creating an external voltage drop in

series with the upper transistor in the

output H-bridge, see figure 5. The

voltage drop reduces the collector-

emitter saturation voltage of the internal

transistor, which can greatly reduce

power dissipation of the IC itself. The

series resistor, designated RB , shall be

selected for about 0.5 V voltage drop at

the maximum output current. In an

application with an output current of

1000 mA (peak), a 0.47 ohm,

1/2 W resistor is the best choice.

In low current applications where

power dissipation is not a critical factor,

the R resistor can of course be omitted,

B

and the VMM and VBB pins (pins 5, 11, 18,

27) can all be connected directly to the

motor supply voltage VMM.

External recirculation diodes

VMM

1

RB

VBB

2

3

RS

Motor Current

1

2

Fast Current Decay

Slow Current Decay

3

Time

+5 V

V MM

0.1 mF

22

RB

RB

0.5 W

18

11

27

0.5 W

5

V

CC

19

V

MM1

V

BB1

V

MM2

V

BB2

MA1

Phase 1

20

V

R1

26

Phase

2

25

MB1

PBL 3772/1

M A2

V R2

M B2

RC GND

23

+5 V 15 kW

3300 pF

1, 2,

3, 9,

28, 13,

14, 15,

16, 17,

C1

E1 C 2

E2

21 10 24

6

1 kW

1 kW

820 pF

RS

820 pF

RS

GND (VCC )

0.5 W 0.5 W

D1 D2

12

+

10 mF

8

4

7

STEPPER

MOTOR

D3 D4

V MM

D1 - D4 are UF 4001 or

BYV 27, t rr £ 100 ns.

Pin numbers GND (VMM)

refer to PLCC

package.

Figure 5. Output stage with current paths Figure 6. Typical stepper motor driver application with PBL 3772/1.

during turn-on, turn-off and phase shift.

5

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