1998 Apr 21

6

Philips Semiconductors

Product specification

32 kHz watch circuits with adaptive motor

pulse

PCA148x series

Detection criteria

The PCA148x uses current detection in two defined parts

of the detection phase to determine if the motor has moved

(refer to Figs 5 and 6). The detection criteria are:

part 1

• Minimum value of P = 1; where P = number of

part 2

• Minimum value of N = 2; where N = number of

measured positive current polarities since the first

negative current polarity after part 1 was detected

(see Fig.5).

If the opposite polarity is measured in one part, the internal

counter is reset, so the results of all measurements in this

part are ignored.

The waveform of the induced current must enable all these

motor pulse in order to be accepted as a waveform of an

executed motor pulse.

If the detection criterion is satisfied earlier, a measurement

cycle will not be started and the switches P1 and P2 stay

detailed in Table 1.

Note that detection and pulse width control will be switched

OFF when the battery voltage is below the end-of-life

motor.

Table 1

Measurement cycle

SYMBOL

PHASE

DESCRIPTION

1

induced current flows unaffected through the motor inductance.

2

Depending on the direction of the interrupted current:

• The current flows through diodes D3 and D2, causing the voltage at M1 to decrease in

relation to M2;

• The current flows through diodes D4 and D1, causing the voltage at M2 to decrease in

relation to M1.

A successfully detected current polarity is normally characterized by a short pulse of

0.5 to 10

µs with a voltage up to ±2.1 V, failed polarity detection by the maximum pulse width

of 61

µs and a voltage of ±0.5 V (see Fig.6).

3

4

reduce the induced current. Therefore P2 and P1 are opened and N1 and N2 are closed.

Otherwise P1 and P2 remain closed.