PBL 3775/1

8

Half-step mode. In the half-step mode,

the current in one winding is brought to

zero before a complete current reversal

is made. The motor will then have taken

two half steps equalling one full step in

rotary movement. The cycle is repeated,

but on the other phase. A total of eight

states are sequenced until the initial

state is reached again.

Half-step mode can overcome

potential resonance problems. Resonan-

ces appear as a sudden loss of torque at

one or more distinct stepping rates and

must be avoided so as not to loose

control of the motor´s shaft position.

One disadvantage with the half-step

mode is the reduced torque in the half

step positions, in which current flows

through one winding only. The torque in

this position is approximately 70 % of the

full step position torque.

Modified half-step mode.The torque

variations in half step mode will be elimi-

nated if the current is increased about

1.4 times in the halfstep position. A

constant torque will further reduce

resonances and mechanical noise,

resulting in better performance, life

expectancy and reliability of the mecha-

nical system.

Modifying the current levels must be

done by bringing the reference voltage

up (or down) from its nominal value

correspondingly. This can be done by

using DACs or simple resistor divider

networks. The PBL 3775/1 is designed

to handle about 1.4 times higher current

in one channel on mode, for example 2

x 500 mA in the full-step position, and 1

x 700 mA in the half-step position.

Figure 14. Typical thermal resistance vs. PC Board copper area and suggested layout.

Figure 15. Stepping modes.

Information given in this data sheet is believed to be

accurate and reliable. However no responsibility is

assumed for the consequences of its use 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 Ericsson Components. These products are sold only

according to Ericsson Components' general conditions of

sale, unless otherwise confirmed in writing.

Specifications subject to change without notice.

1522-PBL 3775/1 Uen Rev. F

© Ericsson Components AB 1999

Ericsson Components AB

SE-164 81 Kista-Stockholm, Sweden

Telephone: +46 8 757 50 00

Thermal resistance [

°C/W]

PCB copper foil area [cm ]

2

80

70

60

50

40

30

20

510

15

20

30

35

25

PLCC package

DIP package

V

R1

Dis

1

Phase

1

Phase

2

Dis

2

I

MA1

I

MA2

100%

–100%

–100%

100%

Full step mode

Half step mode

Modified half step mode

V

R2

140%

100%

140%

100%

140%

–140%

140%

–140%

Ordering Information

Package

Part No.

DIP Tube

PBL 3775/1NS

PLCC Tube

PBL 3775/1QNS

PLCC Tape & Reel

PBL 3775/1QNT

SO Tube

PBL 3775/1SOS

SO Tape & Reel

PBL 3775/1SOT

16-pin

DIP

20-pin

SO

28-pin

PLCC