DS1339AU+T

Real Time Clock Overview

The DS1339AU+T is a low-current, I2C serial real-time clock (RTC) manufactured by Analog Devices Inc./Maxim Integrated. It provides seconds, minutes, hours, day, date, month, and year information with automatic leap-year compensation up to the year 2200. The device operates on a primary supply voltage (VCC) ranging from 1.71V to 5.5V and supports a backup supply (VBACKUP) between 1.3V and 3.7V. It features two programmable time-of-day alarms, a programmable square-wave output, and an automatic power-fail detect and switch circuitry that maintains timekeeping during power outages. The component is housed in an 8-pin µSOP package.

Real Time Clock Feature Summary

• I2C Serial Interface: Supports standard mode communication with SCL frequencies up to 400 kHz.
• Automatic Power-Fail Switching: Built-in circuit detects power failures below VPF (typically 1.61V) and switches to VBACKUP without user intervention.
• Trickle-Charger Capability: Internal circuit allows charging of backup batteries or super capacitors via selectable resistors (200Ω, 2kΩ, 4kΩ) and diode configurations.
• Oscillator Stop Flag (OSF): Indicates when the oscillator has stopped, aiding in data validity checks.

Real Time Clock Applications

• Handheld devices such as GPS units and POS terminals
• Consumer electronics including set-top boxes and digital recorders
• Office equipment like fax machines, printers, and copiers
• Medical devices such as glucometers and medicine dispensers
• Telecommunications infrastructure including routers, switches, and servers

Real Time Clock Procurement Notes

Verify the specific suffix 'AU+T' against the manufacturer's current ordering guide to confirm package type (µSOP), temperature range (-40°C to +85°C), and tape-and-reel packaging quantity. Ensure compatibility with system voltage levels, particularly noting that the 200Ω trickle-charge resistor setting requires VCC to remain below 3.63V to prevent excessive current.

Real Time Clock Selection Notes

Select this component for applications requiring low-power timekeeping with automatic backup switching. Ensure the external crystal meets the specified load capacitance (CL = 6pF) and series resistance (ESR up to 60kΩ). Verify that the system microcontroller supports the I2C protocol and can handle the open-drain outputs on SDA and SQW/INT pins with appropriate pull-up resistors.

Real Time Clock Part Context

The DS1339A series serves as a drop-in replacement for the legacy DS1339 RTC. It shares similar functionality but offers enhanced features such as support for high-ESR crystals and improved trickle-charging options. The 'U' designation typically indicates the µSOP package, while '+T' denotes tape-and-reel packaging for automated assembly.

Real Time Clock Replacement Considerations

The DS1339A is explicitly documented as a drop-in replacement for the DS1339. When substituting, verify pinout compatibility and ensure that any existing code handling the older part's specific register behaviors aligns with the DS1339A's control logic, particularly regarding the oscillator stop flag and alarm mask bits.

Real Time Clock FAQ

How does the DS1339AU+T handle power loss?

The device includes a built-in power-sense circuit that automatically switches from the primary VCC supply to the VBACKUP supply when VCC drops below the power-fail voltage (VPF). This ensures continuous operation of the clock, calendar, and alarms without data loss.

What is the maximum ESR supported by the internal oscillator?

The DS1339A oscillator circuit is designed to support external quartz crystals with a series resistance (ESR) of up to 60 kΩ, eliminating the need for additional external components to drive the crystal.

Can the SQW/INT pin be used during battery backup?

Yes, if the Battery-Backed Square-Wave Interrupt (BBSQI) bit in the Control Register is set to logic 1, the SQW/INT output function remains active even when the device is powered solely by the VBACKUP supply.