DS3234SN IC

DS3234SN General Description

The DS3234 is a low-cost, incredibly accurate real-time clock (RTC) for the SPI bus with a built-in temperature-compensated crystal oscillator (TCXO) and crystal. To monitor VCC, the DS3234 includes a precision, temperature-compensated voltage reference, and comparator circuit. The device asserts the RST output and disables read and write access to the part when VCC falls below the power-fail voltage (VPF) and the VBAT threshold. For the purpose of producing a P reset, the RST pin is observed as a pushbutton input. When the main power to the device is interrupted, the device switches to the backup supply input and keeps accurate time.

The DS3234 additionally incorporates 256 bytes of battery-backed SRAM; should there be a major power outage, the power supply attached to the VBAT pin maintains the memory’s contents. Integrating the crystal resonator improves the device’s long-term accuracy and lowers the piece-part count in a manufacturing line. The DS3234 is available in commercial and industrial temperature ranges and is an industry-standard 300-mil, 20-pin SO package.

For months with fewer than 31 days, the date at the end of the month is automatically changed to account for leap years. The clock has an AM/PM indicator and may run on a 12- or 24-hour schedule. There are two programmable time-of-day alarms as well as a programmable square-wave output. An SPI bidirectional bus transfers address and data serially.

DS3234SN Detailed Description

A TCXO and RTC with an integrated crystal and 256 bytes of SRAM, the DS3234. Periodically, an inbuilt sensor measures the temperature and modifies the oscillator load to account for crystal drift brought on by temperature changes. The sampling rates of the DS3234 are user-selectable. This enables the user to choose a temperature sensor sample rate that minimizes current consumption while accommodating a range of temperature change rates. For applications where the ambient temperature changes dramatically over a short period of time, the user should choose a sample rate depending on the anticipated rate of change in temperature, with quicker sample rates.

The TCXO offers a reliable reference clock and keeps the RTC accurate within 2 minutes per year from -40°C to +85°C. At the 32kHz pin, the TCXO frequency output is accessible. The RTC is a low-power clock/calendar with a configurable square-wave output and two time-of-day alerts. The INT/SQW outputs either a square wave or an interrupt signal in response to alarm circumstances. The clock/calendar displays information in seconds, minutes, hours, days, dates, months, and years.

● 32kHz TCXO

The TCXO comprises a temperature sensor, oscillator, and control logic. To calculate the necessary capacitance, the controller reads the temperature sensor on-chip output,  consults a lookup table, adds the aging correction in the AGE register, and then sets the capacitance selection registers. Only when there is a change in the temperature value are new values loaded, including adjustments to the AGE register. Following the initial application of VCC, the temperature is checked once every 64 seconds.

● VBAT Operation

The quantity of operating modes affects the amount of VBAT current used. When the component is powered by VBAT, the timekeeping current (IBATT), which also contains the average temperature conversion current (IBATTC), is drawn.

The temperature conversion current, IBATTC, is provided because the system must withstand the periodic increased current pulse while maintaining an appropriate voltage level. The component pulls the data retention current, or IBATTDR, when the oscillator is stopped (EOSC = 1). This mode can save battery life when maintaining the time and date is not necessary, such as when delivering the finished system to a customer.

● Clock and Calendar

Reading the relevant register bytes yields the time and calendar information. Writing the relevant register bytes sets or initializes the time and calendar data. The time and calendar registers’ data are presented in binary-coded decimal (BCD) format. You can use the DS3234 in 12- or 24-hour mode. The 12- or 24-hour mode choose bit is designated as bit 6 of the hours’ register. High selects the 12-hour mode. Bit 5 is the AM/PM bit in 12-hour mode, with logic-high serving as PM. Bit 5 is the 20-hour bit in 24-hour mode (20-23 hours).

When the years register exceeds from 99 to 00, the month register’s century bit, or bit 7, is toggled. At midnight, a new day of the week is entered. It is up to the user to define the values that represent the days of the week, but they must be in numerical order (for example, if 1 represents Sunday, 2 represents Monday, and so on). Illogical time and date entries cause a function that is undefinable. Secondary (user) buffers are employed when reading or writing the time and date registers to stop errors from occurring when the internal registers are updated.

The user buffers are synced to the internal registers when reading the time and date registers on the falling edge of CS or when the register pointer rolls over to zero. While the clock keeps ticking, the time data is read from these auxiliary registers. In the event that the main registers update during a read, there is no longer a requirement to reread the registers. Every time the second register is written, the countdown chain is restarted. When the last bit of a byte is clock-in, write transfers occur. To prevent rollover problems after resetting the countdown chain, the remaining time and date registers must be written in under a second. If activated, the 1Hz square-wave output switches high 500ms following the second’s data transfer.

Conclusion

The DS3234 is a real-time clock with an inbuilt temperature-compensated crystal oscillator and crystal that is reliable and reasonably priced. It also incorporates 256 bytes of battery-backed SRAM and a precise, temperature-compensated voltage reference and comparator circuit to monitor VCC. The clock offers a 12- or 24-hour schedule option, an AM/PM display, two programmed time-of-day alerts, and a programmable square-wave output. From -40°C to +85°C, the TCXO provides a dependable reference clock and maintains the RTC’s accuracy to within 2 minutes annually.

The DS3234 is provided in a 300-mil, 20-pin SO package and is offered in commercial and industrial temperature ranges. The DS3234 is the perfect option with all these features for applications where precise timekeeping is essential, as in industrial automation, medical equipment, and telecommunications.

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