PCA2003_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 21 July 2009

5 of 21

NXP Semiconductors

PCA2003

32 kHz watch circuit with programmable adaptive motor 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 %

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0.244 ms

0.122 ms

0.98 ms

0.98 ms

0.98 ms

0.98 ms

Fig 5.

Simplified diagram of motor driving and step detection circuit

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MOTOR

MOT1

N1

P1

D1

RD

N2

P2

P4

P3

MOT2