PCA2002 datasheet(5/20 Pages) PHILIPS

5 / 20 page

2004 Jan 20

Philips Semiconductors

Product speciﬁcation

32 kHz watch circuit with programmable

output period and pulse width

PCA2002

Time calibration

The crystal oscillator has an integrated load capacitance of

5 pF, which is lower than the specified load capacitance of

8.2 pF for the quartz crystal.

It oscillates therefore, at a frequency which is typically

60 ppm higher than 32.768 kHz. This positive frequency

offset is then compensated by removing, every minute or

every two minutes, the appropriate number of 8192 Hz

pulses (maximum 127 pulses) of the divider chain. The

timing correction is given in Table 1.

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 “Programming procedure”.

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

“Programming procedure”.

1024

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osc

Table 1

Timing correction

CALIBRATION

PERIOD (min)

CORRECTION PER STEP (N = 1)

CORRECTION PER STEP (N = 127)

ppm

s/day

ppm

s/day

2.03

0.176

258

22.3

1.017

0.088

129

11.15

Reset

At pin RESET an output signal with a frequency of

= 32 Hz is provided.

Connecting pin RESET to VDD stops the motor drive and

opens the motor switches.

After releasing pin RESET, the first motor pulse is

generated exactly one period later with the opposite

polarity to the last pulse before stopping. The debounce

time for the reset function is between 31 ms and 62 ms.

Connecting pin RESET to VSS activates the test mode.

In this mode the motor output frequency is 32 Hz, which

can be used to test the mechanical function of the watch.

Programming possibilities

The programming data is stored in two words; see Table 2.

1024

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osc

Table 2

Words and bits

WORD

BIT

1234567

number of 8192 Hz pulses to be removed

calibration period

pulse width

output period

duty cycle

pulse stretching

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