NXP Semiconductors PCF2123U/12AA/1,00

Overview

PCF2123U/12AA/1,00 from NXP Semiconductors is a low-power SPI Real-Time Clock (RTC) and calendar IC with integrated 32.768 kHz oscillator, 6.25 Mbit/s SPI interface, open-drain interrupt output, programmable offset register for ±127 ppm fine-tuning, and 1.1 V to 5.5 V operating voltage - deployed in battery-powered metering and portable medical devices requiring sub-100 nA backup current.

For engineers reviewing the PCF2123U/12AA/1,00 datasheet, PCF2123U/12AA/1,00 pinout, PCF2123U/12AA/1,00 application, or PCF2123U/12AA/1,00 equivalent, this page delivers verified specifications, WLCSP12 package mapping, BCD-encoded time registers, alarm/timer interrupt behavior, and direct alternatives for low-power timekeeping design-in.

Technical Context

The PCF2123U/12AA/1,00 implements a fully autonomous RTC core driven by an on-chip 32.768 kHz oscillator with integrated 7 pF load capacitors, eliminating external crystal tuning components. Its 16-register memory map includes BCD-coded time/date counters (seconds to years), four alarm registers with independent enable bits, and dual timer functions: pre-defined 1-second/1-minute interrupts plus a configurable countdown timer with selectable source clocks (4.096 kHz to 1/60 Hz).

Communication occurs via a 3-wire SPI bus (CE, SCL, SDI/SDO) supporting up to 6.25 Mbit/s, with CE-active HIGH protocol and push-pull SDO/open-drain INT/CLKOUT outputs. Internal Power-On Reset (POR) and software reset (0x58 command) ensure deterministic initialization, while the OS flag in the Seconds register enables oscillator health monitoring during brown-out conditions.

Key Specifications

Pinout & Package

PCF2123U/12AA/1,00 is supplied in a WLCSP12 (Wafer Level Chip Size Package) with 12 solder bumps, footprint size 1.63 mm × 1.63 mm × 0.54 mm, suitable for space-constrained wearables and implantables. Pin assignments follow die-level bonding pad layout per Figure 4 of NXP Rev. 6 datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar real-time clock applications.

Compared with PCF2123U/12AA/1,00, DS3231M trades SPI compatibility and lower quiescent current for superior temperature-compensated accuracy, while RV-3028-C7 reduces footprint and adds interface flexibility at the cost of added BOM complexity and slightly higher backup current.

Availability

PCF2123U/12AA/1,00 is available at Aetrix Electronics and suitable for metering, portable medical devices, industrial IoT sensors, and asset tracking tags requiring stable component supply across long-lifecycle deployments.

Supply support for PCF2123U/12AA/1,00 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

NXP Semiconductors is a global semiconductor leader focused on secure connectivity solutions for automotive, industrial, and IoT markets, with over 50 years of analog and mixed-signal IP expertise.

The PCF2123U/12AA/1,00 belongs to NXP's ultra-low-power RTC product line, designed specifically for battery-operated edge devices demanding decade-long runtime, robust timekeeping under voltage stress, and minimal PCB footprint.

FAQ

What is the backup current specification for PCF2123U/12AA/1,00 at 2.0 V?

The PCF2123U/12AA/1,00 draws typical 100 nA backup current at VDD = 2.0 V and Tamb = 25 °C, measured with CLKOUT disabled and timer clock set to 1/60 Hz. This value scales with quartz series resistance and timer clock selection - lower Rs and slower timer clocks further reduce current. The PCF2123U/12AA/1,00 achieves this performance using optimized CMOS design and integrated oscillator load capacitors.

Does PCF2123U/12AA/1,00 support SPI mode 0 (CPOL=0, CPHA=0)?

Yes, PCF2123U/12AA/1,00 operates exclusively in SPI Mode 0: clock polarity (CPOL) is 0 (idle LOW) and clock phase (CPHA) is 0 (data sampled on first edge). The SCL input is sampled on the rising edge, and data is shifted out on SDO on the falling edge. This timing aligns with standard 8051 and ARM Cortex-M SPI peripherals without configuration overrides.

How is time/date data encoded in PCF2123U/12AA/1,00 registers?

All time/date registers (02h–08h) in PCF2123U/12AA/1,00 use Binary-Coded Decimal (BCD) format - seconds, minutes, hours, days, weekdays, months, and years are stored as two 4-bit nibbles per byte. For example, 0x23 in the Minutes register represents 23 decimal, not 35. This encoding simplifies firmware parsing and avoids overflow errors during arithmetic operations.

Can PCF2123U/12AA/1,00 generate a 1-second interrupt without external components?

Yes, PCF2123U/12AA/1,00 supports a dedicated 1-second interrupt via bit SI (Second Interrupt Enable) in Control_2 register (01h). When enabled, it asserts the open-drain INT pin once per second - no external timer or MCU polling required. The interrupt remains active until cleared by writing to Control_2, and coexists with alarm and timer interrupts.

What is the function of the OS flag in the Seconds register of PCF2123U/12AA/1,00?

The OS (Oscillator Stop) flag is bit 7 of the Seconds register (02h) in PCF2123U/12AA/1,00. It is set automatically when the 32.768 kHz oscillator stops due to low VDD, crystal disconnection, or mechanical shock. The flag remains latched until cleared by firmware, enabling reliable detection of timekeeping failures without external monitoring circuitry.