PCA2003_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 21 July 2009

7 of 21

NXP Semiconductors

PCA2003

32 kHz watch circuit with programmable adaptive motor 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 7.7).

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, which originates from the

time calibration, depending on the programmed calibration period.

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

are given in Section 7.10.

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.

7.5 Programming possibilities

The programming data is stored in OTP cells (EPROM cells). At delivery, all memory cells

are in state 0. The cells can be programmed to the state 1, but then there is no more set

back to state 0.

The programming data is organized in an array of four 8-bit words: word A contains the

time calibration, words B and C contain the setting for the monitor pulses and word D

contains the type recognition (see Table 4).

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

=