2003 Dec 17

4

Philips Semiconductors

Product specification

32 kHz watch circuit with programmable

adaptive motor pulse

PCA2000; PCA2001

FUNCTIONAL DESCRIPTION

Motor pulse

The motor output supplies pulses of different driving

stages, depending on the torque required to turn on the

motor. The number of different stages can be selected

between three and six. With the exception of the highest

followed by a detection phase during which the motor

movement is monitored, in order to check whether the

motor has turned correctly or not.

If a missing step is detected, a correction sequence is

generated (see Fig.3) and the driving stage is switched to

the next level. The correction sequence consists of two

pulses: first a short pulse in the opposite direction

(0.98 ms, modulated with the maximum duty cycle) to give

the motor a defined position, followed by a motor pulse of

the strongest driving level. Every 4 minutes, the driving

level is lowered again by one stage.

The motor pulse has a constant pulse width. The driving

level is regulated by chopping the driving pulse with a

variable duty cycle. The driving level starts from the

programmed minimum value and increases by 6.25% after

each failed motor step. The strongest driving stage, which

is not followed by a detection phase, is programmed

separately.

Therefore, it is possible to program a larger energy gap

between the pulses with step detection and the strongest,

not monitored, pulse. This might be necessary to ensure a

reliable and stable operation under adverse conditions

(magnetic fields, vibrations). If the watch works in the

highest driving stage, the driving level jumps after the

4-minute period directly to the lowest stage, and not just

one stage lower.

To optimize the performance for different motors, the

following parameters can be programmed:

• Pulse width: 0.98 to 7.8 ms in steps of 0.98 ms

• Duty cycle of lowest driving level: 37.5% to 56.25% in

steps of 6.25%

• Number of driving levels (including the highest driving

level): 3 to 6

• Duty cycle of the highest driving level: 75% or 100%

• Enlargement pulse for the highest driving level: on or off.

The enlargement pulse has a duty cycle of 25% and a

pulse width which is twice the programmed motor pulse

width. The repetition period for the chopping pattern is

0.98 ms. Figure 4 shows an example of a 3.9 ms pulse.

handbook, full pagewidth

31.25 ms

1.96 ms

detection phase

tp

31.25 ms

0.98 ms

tp

2tp

MGW350

Fig.3 Correction sequence after failed motor step.