1.

General description

The PCA2000 and PCA2001 are CMOS integrated circuits for battery operated wrist

watches with a 32 kHz quartz crystal as timing element and a bipolar 1 Hz stepping motor.

The quartz crystal oscillator and the frequency divider are optimized for minimum power

consumption. A timing accuracy of 1 ppm is achieved with a programmable, digital

frequency adjustment.

To obtain the minimum overall power consumption for the watch, an automatic motor

pulse adaptation function is provided. The circuit supplies only the minimum drive current,

which is necessary to ensure a correct motor step. Changing the drive current of the

motor is achieved by chopping the motor pulse with a variable duty cycle. The pulse width

and the range of the variable duty cycle can be programmed to suit different types of

motors. The automatic pulse adaptation scheme is based on a safe dynamic detection of

successful motor steps.

A pad RESET is provided (used for stopping the motor) for accurate time setting and for

accelerated testing of the watch.

The PCA2000 has a battery End Of Life (EOL) warning function. If the battery voltage

drops below the EOL threshold voltage (which can be programmed for silver oxide or

lithium batteries), the motor steps change from one pulse per second to a burst of four

pulses every 4 seconds.

The PCA2001 uses the same circuit as the PCA2000, but without the EOL function.

2.

Features

and high immunity to leakage currents

Programmable (OTP) memory

drive according to the required torque

wide range, stored in OTP memory

PCA2000; PCA2001

32 kHz watch circuit with programmable adaptive motor pulse

Rev. 05 — 11 November 2008

Product data sheet