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 benefits

Amplitude-regulated 32 kHz quartz crystal oscillator, with excellent frequency stability

and high immunity to leakage currents

Electrically programmable time calibration with 1 ppm resolution stored in One Time

Programmable (OTP) memory

The quartz crystal is the only external component connected

Very low power consumption, typical 90 nA

One second output pulses for bipolar stepping motor

Minimum power consumption for the entire watch, due to self adaptation of the motor

drive according to the required torque

Reliable step detection circuit

Motor pulse width, pulse modulation, and pulse adaptation range programmable in a

wide range, stored in OTP memory

Stop function for accurate time setting and power saving during shelf life

PCA2000; PCA2001

32 kHz watch circuit with programmable adaptive motor pulse

Rev. 08 — 23 August 2010

Product data sheet