PCA2000_2001

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Product data sheet

Rev. 08 — 23 August 2010

6 of 30

NXP Semiconductors

PCA2000; PCA2001

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.

The step detection phase is initiated after the motor driving pulse. In phase 1 P1 and P2

are first closed for 0.98 ms and then in phase 2 all four drive switches (P1, N1, P2 and N2)

are opened for 0.98 ms. As a result, the energy stored in the motor inductance is reduced

as fast as possible.

The induced current caused by the residual motor movement is then sampled in phase 3

(closing P3 and P2) and in phase 4 (closing P1 and P4). For step detection in the opposite

direction P1 and P4 are closed during phase 3 and P2 and P3 during phase 4 (see

Figure 6).

Fig 5.

Simplified diagram of motor driving and step detection circuit

mgw352

MOTOR

MOT1

N1

P1

D1

RD

N2

P2

P4

P3

MOT2