The PCA2000 and PCA2001 are CMOS integrated circuits for battery operated wristwatches 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 powerconsumption. A timing accuracy of 1 ppm is achieved with a programmable, digitalfrequency adjustment.
To obtain the minimum overall power consumption for the watch, an automatic motorpulse 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 themotor is achieved by chopping the motor pulse with a variable duty cycle. The pulse widthand the range of the variable duty cycle can be programmed to suit different types ofmotors. The automatic pulse adaptation scheme is based on a safe dynamic detection ofsuccessful motor steps.
A pad RESET is provided (used for stopping the motor) for accurate time setting and foraccelerated testing of the watch.
The PCA2000 has a battery End Of Life (EOL) warning function. If the battery voltagedrops below the EOL threshold voltage (which can be programmed for silver oxide orlithium batteries), the motor steps change from one pulse per second to a burst of fourpulses every 4 seconds.
The PCA2001 uses the same circuit as the PCA2000, but without the EOL function.
Feature
- Amplitude-regulated 32 kHz quartz crystal oscillator, with excellent frequency stabilityand high immunity to leakage currents
- Electrically programmable time calibration with 1 ppm resolution stored in One TimeProgrammable (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 motordrive according to the required torque
- Reliable step detection circuit
- Motor pulse width, pulse modulation, and pulse adaptation range programmable in awide range, stored in OTP memory
- Stop function for accurate time setting and power saving during shelf life
- End Of Life (EOL) indication for silver oxide or lithium battery (only the PCA2000 hasthe EOL feature)
- Test mode for accelerated testing of the mechanical parts of the watch and the IC
- Test bits for type recognition
- Driver circuits for bipolar stepping motors
- High immunity motor drive circuits
