PCA2000_2001_5

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 05 — 11 November 2008

5 of 28

NXP Semiconductors

PCA2000; PCA2001

32 kHz watch circuit with programmable adaptive motor pulse

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.

7.2 Step detection

Figure 5 shows a simplified diagram of the motor driving and step detection circuit, and

Figure 6 shows the step detection sequence and corresponding sampling current.

Between the motor driving pulses, the switches P1 and P2 are closed, which means the

motor is short-circuited. For a pulse in one direction, P1 and N2 are open, and P2 and N1

are closed with the appropriate duty cycle; for a pulse in the opposite direction, P2 and N1

are open, and P1 and N2 closed.

Fig 4.

Possible modulations for a 3.9 ms motor pulse

43.75 %

37.5 %

DUTY CYCLE

50 %

56.25 %

62.5 %

68.75 %

75 %

81.25 %

100 %

mgw351

0.244 ms

0.122 ms

0.98 ms

0.98 ms

0.98 ms

0.98 ms