Electronics Weekly
The chip is called MAX31341B.
“Systems that use microcontrollers for accurate timekeeping waste battery life, which is unacceptable in wearable applications. MAX31341B is designed with power-management circuitry that remains on during dormant periods, providing timekeeping so that the microcontroller shuts down to preserve power and extend battery life,” according to the firm, which added that power is 18% less than its closest competitor.
Over a decade of operation is expected from a lithium coin-cell in battery back-up mode.
On board is an integrated load capacitor (supporting 6pF crystals with ESR up to 100kΩ), a trickle charger, power management and a 64byte RAM.
“As the industry’s only RTC with power-management capabilities, it can off-load the application processor of the timekeeping task and remain as the only device that is on when a [host] device is not in use,” said Maxim business director Binay Bajaj.
The power management block monitors the supply voltage on Vcc and back-up battery voltage (via the ‘Ain’ battery connection pin), and determines which source is used as the internal power supply, while the trickle charge is an even simpler affair, also using the Ain pin, available to charge an external super-capacitor or a rechargeable battery via a choice of three resistors.
Operation is over -40 to +85°C, and accuracy can be as good as 100ppm , depending on the external crystal.
Data is accessed through an I2C serial interface and it has one digital Schmitt trigger input as well as one programmable-threshold analogue input (yet again sharing the Ain pin), and generates an interrupt output on a falling or rising edge of the digital input, or when the analogue input voltage crosses a programmed threshold in either direction.
An integrated power-on reset ensures deterministic default register status upon power-up.
Other features include two time-of-day alarms, a programmable square-wave output and a serial bus time-out mechanism.
The clock/calendar provides seconds, minutes and hours in 24-hour format, then day, date, month and year information. Date at the end of the month is automatically adjusted for months with fewer than 31 days, including 29 day Februaries at leap year. On top of this, there is a count-down timer.
In addition to the quartz input, the chip includes an input for synchronisation to a reference clock, which can be one of: 32.768kHz, 50Hz (mains), 60Hz (mains) or 1Hz (GPS). An alarm is set if the reference differs from chips own crystal-derived signal by >±0.8%.
The package is a 12bump 0.5mm pitch WLP.
There is an evaluation kit: MAX31341BEVKIT#
Does no one check those figures?
The current draw would have to be a lot less than 180 micro amp to last 10+ years on a lithium coin cell. The typical cell used in backup applications is the CR2032 which has a nominal capacity of 100mAh so to last 10+ years would require a current draw of 1 micro amp or less. Perhaps the figure should be nano amps?
P.S. Thirty years ago I had a Casio digital watch with a smaller coin cell and it could last 7 years and work a display as well so Maxim’s boast represents no progress in decades.
Mea culpa – it is my fault entirely. The current is 180nA, and I have now corrected the article.
As to the question does no one check those figures? I spend much of my time checking information provided to Electronics Weekly back to the data sheets, and have even found errors in a couple of data sheets, but am sadly fallible – and a rubbish typist.
Thanks for pointing out the error.