PCA2003_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 21 July 2009

4 of 21

NXP Semiconductors

PCA2003

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:

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

31.25 ms

1.96 ms

detection phase

31.25 ms

0.98 ms

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