DS1388Z-5+

Real Time Clock Overview

The DS1388Z-5+ is an I2C real-time clock, supervisor, and EEPROM device from Analog Devices/Maxim Integrated. It provides a clock/calendar with hundredths-of-seconds resolution, operating in 24-hour or 12-hour formats with leap year compensation valid through 2100. The device includes 512 bytes of EEPROM, a programmable watchdog timer (0.01 to 99.99 seconds), and power-supply monitoring with reset output. It supports automatic switching between primary VCC (4.5V–5.5V) and backup supply (1.3V–5.5V). Key features include a fast 400kHz I2C interface, integrated trickle charger for backup cells, pushbutton reset controller, and operation across -40°C to +85°C.

Real Time Clock Feature Summary

• I2C RTC with Calendar/Clock: Hundredths-of-seconds, seconds, minutes, hours, day, date, month, year; 12/24 hour modes; Leap year correction to 2100.
• Supervisor Functions: Programmable watchdog timer (0.01s–99.99s); Power-fail detect and switch; Reset output with pushbutton debounce.
• Memory: 512 Bytes EEPROM (two 256-byte blocks); Battery-backed timekeeping registers.
• Trickle Charger: Integrated circuitry for charging backup supplies via selectable resistors (250Ω, 2kΩ, 4kΩ) and diode options.

Real Time Clock Applications

• Portable Instruments
• Point-of-Sale Equipment
• Network Interface Cards
• Wireless Equipment

Real Time Clock Procurement Notes

Verify the specific voltage suffix '5' indicates the 4.5V–5.5V operating range. Confirm package type is 8-pin SOIC (150 mils). Check RoHS compliance status (+ denotes lead-free/RoHS-compliant). Ensure backup supply voltage requirements align with the 1.3V–5.5V VBACKUP specification.

Real Time Clock Selection Notes

Select DS1388Z-5+ for systems requiring 5V logic levels and I2C communication. Compare against DS1388Z-33+ (3.3V) or DS1388Z-3+ (3.0V) if lower voltage operation is needed. Consider the integrated watchdog and supervisor functions which eliminate external components for system reset management. Verify crystal load capacitance (6pF typical) for oscillator accuracy.

Real Time Clock Part Context

The DS1388Z-5+ belongs to the DS1388 family of multifunction RTCs. It integrates timekeeping, non-volatile memory, and system supervision into a single 8-pin package. The 'Z' indicates RoHS compliance, and '+' confirms lead-free packaging. It is designed to replace discrete RTC, EEPROM, and supervisor ICs in space-constrained designs.

Real Time Clock Replacement Considerations

DS1388Z-33+ (3.3V version), DS1388Z-3+ (3.0V version). Note that these variants differ only in recommended DC operating conditions for VCC.

Real Time Clock FAQ

How does the device handle power failure?

The DS1388 monitors VCC. If VCC falls below the power-fail voltage (VPF), it automatically switches to the VBACKUP supply and drives the RST pin low. Timekeeping continues on VBACKUP until VCC returns to nominal levels.

What is the function of the RST pin?

The RST pin is an active-low open-drain output indicating VCC status relative to VPF. It also serves as a debounced pushbutton reset input. When VCC drops below VPF, RST goes low. It can also be pulsed low by the watchdog timer if enabled.

Can the watchdog timer be disabled?

Yes. Setting the WDE bit in the Control Register (0Ch) to logic 0 disables the watchdog counter. In this state, the two watchdog registers can be used as general-purpose NV RAM.

What are the constraints on the trickle charger resistor selection?

The 250Ω resistor option must not be selected when VCC is greater than 3.63V. For the DS1388Z-5+ (VCC up to 5.5V), users must select either the 2kΩ or 4kΩ resistor options to prevent excessive current.