
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
driving stage, each motor pulse (t
p
in Figs 3 and 6) is
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
programmedminimumvalueandincreasesby6.25%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.