32 KHz Watch Circuit with Programmable Adaptive Motor Pulse and Pulse Period

PCA2003U

The PCA2003 is a CMOS integrated circuit 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 period 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.

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PCA2003 -BD

PCA2003 Block Diagram

Block diagram: PCA2003U

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Features

  • 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 supply current, typical 90 nA
  • One second output pulses for bipolar stepping motor
  • Five different programmable output periods (1 s to 30 s)
  • 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
  • Test mode for accelerated testing of the mechanical parts of the watch and the IC
  • Test bits for type recognition

Target Applications

  • Driver circuits for bipolar stepping motors
  • High immunity motor drive circuits

部品番号： PCA2003U.

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