Analog Devices Inc./Maxim Integrated DS1340C-18#

Overview

DS1340C-18# from Maxim Integrated is a surface-mount I²C real-time clock/calendar with integrated 32.768kHz crystal, trickle-charge capability on VBACKUP, oscillator stop flag (OSF), and low timekeeping voltage down to 1.3V. It operates across -40°C to +85°C, supports 1.8V supply, and delivers BCD-formatted time/date (seconds to year) with automatic leap-year correction-used in portable medical instruments requiring battery-backed timekeeping with minimal PCB footprint.

For engineers reviewing the DS1340C-18# datasheet, DS1340C-18# pinout, DS1340C-18# application, or DS1340C-18# equivalent, key selection criteria include its 16-pin SO package with integrated crystal, 400kHz I²C interface, VBACKUP trickle-charge resistor configuration (250Ω/2kΩ/4kΩ), OSF flag for oscillator health monitoring, and software calibration via CAL[4:0] bits with ±4.068ppm/−2.034ppm per step.

Technical Context

The DS1340C-18# implements a precision temperature-compensated power-fail detection circuit that switches between VCC and VBACKUP when VCC drops below VPF (1.51–1.71V), maintaining register integrity without halting timekeeping. Its internal oscillator drives a divider chain synchronized to secondary buffers during I²C reads, eliminating read-race conditions.

Trickle charging is enabled only by the exact TCS[3:0] = 1010 pattern in register 08h, selecting diode/resistor combinations (e.g., one diode + 2kΩ) to limit charge current; the OSF bit is edge-triggered and latched until explicitly cleared, providing deterministic oscillator fault detection independent of VCC/VBACKUP voltage levels.

Key Specifications

Pinout & Package

DS1340C-18# uses a 16-pin small-outline (SO) package with integrated crystal; pins 4–13 are No Connect (N.C.) and must be grounded per datasheet requirement. The package includes internal bias network and crystal mounting structure, eliminating external CL tuning components.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar RTC applications.

Compared with DS1340C-18#, the M41T00M6F requires additional passive components and offers no timekeeping calibration, while the DS3231SN delivers superior accuracy but removes the ability to recharge backup sources-making DS1340C-18# optimal for space-constrained, battery-charged embedded systems needing moderate accuracy and integrated crystal simplicity.

Availability

DS1340C-18# is available at Aetrix Electronics and suitable for portable medical monitors, point-of-sale terminals, and industrial data loggers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for DS1340C-18# includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog and mixed-signal ICs for power, sensing, and timing applications, with emphasis on low-power, high-reliability solutions for industrial and medical markets.

The DS1340 product line delivers highly integrated RTCs with backup power management, targeting applications where board space, battery life, and time validity assurance are critical-such as handheld diagnostics and edge telemetry devices.

FAQ

What is the function of the OSF bit in DS1340C-18#?

The OSF (Oscillator Stop Flag) bit in DS1340C-18# is a latched status indicator located in register 09h, bit 7. It asserts logic 1 when the internal 32.768kHz oscillator halts due to power loss, crystal fault, EOSC disable, or noise interference. DS1340C-18# retains this flag until firmware explicitly writes 0 to it, enabling reliable validation of time/date validity before use in safety-critical logs or audits.

How does DS1340C-18# handle power switching between VCC and VBACKUP?

DS1340C-18# uses an internal comparator with a 1.51V–1.71V VPF threshold to monitor VCC. When VCC falls below VPF, DS1340C-18# automatically switches power to VBACKUP while blocking register access-but continues timekeeping uninterrupted. Upon VCC recovery above VPF, DS1340C-18# waits 2ms (tREC) before re-enabling I²C access, ensuring stable register state restoration.

Can DS1340C-18# operate with a 3.3V supply?

Yes, DS1340C-18# supports 3.3V operation: its VCC range spans 1.71V to 5.5V, and the "-18" suffix denotes 1.8V nominal compatibility-not exclusivity. At 3.3V, DS1340C-18# draws 108–200μA active current and maintains full I²C functionality, including 400kHz Fast Mode, while retaining all features like trickle charging and OSF flag reporting.

What is the purpose of the TCS bits in DS1340C-18# register 08h?

The TCS[3:0] bits (bits 7–4) in DS1340C-18# register 08h control trickle-charge activation and configuration. Only the binary pattern 1010 enables charging; all other values disable it. When enabled, DS1340C-18# uses these bits alongside DS[1:0] and ROUT[1:0] to select diode presence and current-limiting resistor value (250Ω/2kΩ/4kΩ), allowing safe, programmable charging of VBACKUP sources like supercaps.

Does DS1340C-18# require external load capacitors for its integrated crystal?

No, DS1340C-18# does not require external load capacitors. Its integrated 32.768kHz crystal is factory-matched to the internal oscillator's 12.5pF capacitive load, eliminating CL tuning components. This integration reduces PCB area, simplifies layout, and improves EMI immunity-confirmed in the DS1340C-specific section of the datasheet, which states "no external resistors or capacitors to operate."