1998 Apr 21

3

Philips Semiconductors

Product specification

32 kHz watch circuits with adaptive motor

pulse

PCA148x series

FUNCTIONAL DESCRIPTION AND TESTING

The motor output delivers pulses of six different stages

depending on the torque required to turn the motor (Fig.3).

Every motor pulse is followed by a detection phase which

monitors the waveform of the induced motor voltage.

When a step is missed a correction sequence will be

started (Fig.2).

Motor pulses

The circuit produces motor pulses of six different stages

(stage 1 to 5, stage 6).

Stages 1 to 5 are used in normal operation, stage 6 occurs

under the following conditions:

• Correction pulse after a missing step

• End-of-life mode

• If stage 5 is not enough to turn the motor.

The ON state of the motor pulse varies between 43.75%

stage (Fig.3). It increases in steps of 6.25% per stage.

After a RESET the circuit always starts and continues with

stage 1, when all motor pulses have been executed.

A failure to execute all motor pulses results in the circuit

going into stage 2, this sequence will be repeated through

to stage 6.

When the motor pulses at stage 5 are not large enough to

turn the motor, stage 6 is implemented for a maximum of

8 minutes with no attempt to keep current consumption

low. After stage 6 has been executed the procedure is

repeated from RESET.

The circuit operates for 8 minutes at a fixed stage, if every

motor pulse is executed. The next 480 motor pulses are

then produced at the next lower stage unless a missing

step is detected. If a step is missed a correction sequence

is produced and for a maximum of 8 minutes the motor

pulses are increased by one stage.

Fig.2 Possible motor output waveform in normal operation with motor connected.

MSA969

MOTOR

PULSE

DETECTION

t P

t D

t C

POSSIBLE CORRECTION

SEQUENCE

t T

M1 - M2

V