PCA2000_2001_5

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 05 — 11 November 2008

7 of 28

NXP Semiconductors

PCA2000; PCA2001

32 kHz watch circuit with programmable adaptive motor pulse

The condition for a successful motor step is a positive step detection pulse (current in the

same direction as in the driving phase) followed by a negative detection pulse within a

given time limit. This time limit can be programmed between 3.9 ms and 10.7 ms (in steps

of 0.98 ms) in order to ensure a safe and correct step detection under all conditions (for

instance magnetic fields). The step detection phase stops after the last 31.25 ms, after the

start of the motor driving pulse.

7.3 Time calibration

The quartz crystal oscillator has an integrated capacitance of 5.2 pF, which is lower than

the oscillator frequency is typically 60 ppm higher than 32.768 kHz. This positive

frequency offset is compensated by removing the appropriate number of 8192 Hz pulses

in the divider chain (maximum 127 pulses), every 1 or 2 minutes. The time correction is

given in Table 3.

After measuring the effective oscillator frequency, the number of correction pulses must

be calculated and stored together with the calibration period in the OTP memory (see

Section 7.8).

The oscillator frequency can be measured at pad RESET, where a square wave signal

with the frequency of

is provided.

This frequency shows a jitter every minute or every two minutes, depending on the

programmed calibration period, which originates from the time calibration.

Details on how to measure the oscillator frequency and the programmed inhibition time

are given in Section 7.11.

7.4 Reset

At pad RESET an output signal with a frequency of

is provided.

mode. In this mode the motor output frequency is 32 Hz, which can be used to test the

mechanical function of the watch.

After releasing the pad RESET, the motor starts exactly one second later with the smallest

duty cycle and with the opposite polarity to the last pulse before stopping.

The debounce time for the RESET function is between 31 ms and 62 ms.

Table 3.

Time calibration

Calibration

period

Correction per step (n = 1)

Correction per step (n = 127)

ppm

seconds per day ppm

seconds per day

1 minute

2.03

0.176

258

22.3

2 minutes

1.017

0.088

129

11.15

1

1024

------------

f

osc

×

1

1024

------------

f

osc

×

32 Hz

=