PCF2003 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 1 — 20 October 2015 4 of 30
NXP Semiconductors
PCF2003
32 kHz watch circuit with programmable adaptive motor pulse
If a missing step is detected, a correction sequence is generated (see Figure 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 and 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 ms 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.
Fig 3. Correction sequence after failed motor step
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