The M41T00AUD is a low-power serial real-time clock (RTC) with an integral audio section with tone generator and 300 mW output amplifier. The RTC is a superset of the M41T00 with enhancements such as a precision reference for switchover, an oscillator fail detect circuit, and storing of the time at power-down. The audio section includes a summing amplifier (inverting) at the input. An 8 kHz low-pass filter follows that with a 16-step programmable gain stage next. A 256 or 512 Hz audio tone can be switched into the filter in place of the input signal. From the gain stage, the 300 mW amplifier drives the output pins.
The M41T00AUD has a built-in power sense circuit which detects power failures and automatically switches to the backup input when VCCis removed. Backup power can be supplied by a capacitor or by a battery such as a lithium coin cell. The device includes a trickle charge circuit for charging the capacitor.
The RTC includes a built-in 32.768 kHz oscillator controlled by an external crystal. Eight register bytes are used for the clock/calendar functions and are superset compatible with the M41T00. Two additional registers control the audio section and the trickle charger. The 10 registers are accessed over a 400 kHz I2C bus. The address register increments automatically after each byte READ or WRITE operation thus streamlining transfers by eliminating the need to send a new address for each byte to be transferred.
Typical data retention times will be in excess of 5 years with a 50 mAh 3 V lithium cell.
Combination real-time clock with audio
Serial real-time clock (RTC) based on M41T00
Audio section provides:
300 mW differential audio amplifier
256 and 512 Hz tone generation
–33 to +12 dB gain, 3 dB steps (16 steps plus MUTE)
0 °C to 70 °C operation
Small DFN16 package (5 mm x 4 mm)
Real-time clock details
Superset of M41T00
3.0 to 3.6 V operation
Timekeeping down to 1.7 V
Automatic backup switchover circuit
Ultra-low 400 nA backup current at 3.0 V (typ)
Suitable for battery or capacitor backup
On-chip trickle charge circuit for backup capacitor
400 kHz I2C bus
M41T00 compatible register set with counters for seconds, minutes, hours, day, date, month, years, and century
Automatic leap year compensation
HT bit set when clock goes into backup mode
RTC operates using 32,768 Hz quartz crystal
Calibration register provides for adjustments of –63 to +126 ppm
Oscillator supports crystals with up to 40 kΩ series resistance, 12.5 pF load capacitance
Oscillator fail detect circuit OF bit indicates when oscillator has stopped for four or more cycles