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Home > Products > Integrated Circuits (ICs) > Clock/Timing > Real Time Clocks

NXP Semiconductors PCF2127AT/1,518

Name: PCF2127AT/1,518
Brand: NXP Semiconductors
SKU: PCF2127AT/1,518
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: PCF2127AT/1,518

Manufacturer:: NXP Semiconductors

Category:: Real Time Clocks

Package:: 20-SOIC (0.295", 7.50mm Width)

Datasheet:: PCF2127AT/1,518.pdf

Description:: IC RTC CLOCK/CALENDAR I2C 20SO

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Product details

Overview

PCF2127AT/1,518 from NXP Semiconductors is a highly accurate, ultra-low-power integrated Real Time Clock (RTC) with on-chip Temperature Compensated Crystal Oscillator (TCXO), 32.768 kHz quartz crystal, 512-byte battery-backed SRAM, and dual I²C/SPI interface - delivering ±3 ppm accuracy from −15 °C to +60 °C for precision timekeeping in metering and GPS applications.

For engineers reviewing the PCF2127AT/1,518 datasheet, PCF2127AT/1,518 pinout, PCF2127AT/1,518 application, or PCF2127AT/1,518 equivalent, key selection considerations include TCXO-integrated timing stability, dual-bus interface flexibility (I²C up to 400 kHz / SPI up to 6.5 Mbit/s), battery switch-over circuitry with timestamp capture on power loss, and programmable watchdog/alarm/timer functions with interrupt outputs.

Technical Context

The PCF2127AT/1,518 implements a fully integrated RTC architecture with temperature-sensing feedback loop that dynamically adjusts crystal load capacitance via factory-calibrated modulation to achieve ±3 ppm accuracy across −15 °C to +60 °C. Its register-mapped memory includes auto-incrementing address pointers for time/date, alarm, timestamp, and watchdog registers - all accessible over either I²C or SPI.

Power management is hardware-automated: VDD-to-VBAT switchover triggers BF flag assertion, optional timestamp logging (via BTSE bit), and automatic interface disablement during backup operation. The device supports 12/24-hour mode, leap-year correction, BCD-encoded time registers, and aging offset compensation (±7 ppm at 25 °C) via dedicated Aging_offset register.

Key Specifications

Parameter	Value and Actual Design Meaning
Timing Accuracy	±3 ppm from −15 °C to +60 °C - enables <1 second/month drift in utility meters and GPS time-to-first-fix reduction
Supply Voltage Range	1.2 V to 4.2 V - supports single-cell Li-ion, coin-cell, or regulated 3.3 V/1.8 V rails without external LDO
Typical Supply Current	0.65 µA at VDD = 3.0 V, Tamb = 25 °C - extends 10-year coin-cell life in unattended metering deployments
Interface Options	I²C Fast-mode (400 kHz) or 3-wire SPI (6.5 Mbit/s) - selectable via IFS pin; SDA/CE serves dual role as I²C data or SPI chip enable
Backup Power Handling	Automatic VDD-to-VBAT switchover with programmable threshold (standard/direct modes); BBS output provides stable battery-backed voltage
On-chip Memory	512 bytes of battery-backed static RAM - retains critical firmware state or calibration data during main power loss
Interrupt Outputs	Open-drain INT (configurable per alarm/watchdog/timestamp), RST (watchdog reset), PFO (power fail), and CLKOUT (programmable 1 Hz–32.768 kHz)

Pinout & Package

PCF2127AT/1,518 is housed in a plastic small outline package (SO20) with 20 leads and 7.5 mm body width (SOT163-1). All pins are electrically defined per NXP Rev. 6 datasheet; pins 9–12 and TEST (13) are no-connect and must remain unconnected.

Pin/Terminal	Circuit Role	Design Meaning
SCL (1)	Serial clock input	Shared clock for both I²C and SPI interfaces; requires external pull-up
SDI (2)	SPI serial data input	Must tie to VSS when I²C mode selected; unused in I²C operation
SDO (3)	SPI serial data output	Push-pull output; not used in I²C mode
SDA/CE (4)	I²C data / SPI chip enable	Bi-directional open-drain I²C data line; active-low SPI chip select
IFS (5)	Interface selector	Connect to VSS for SPI; connect to BBS for I²C - determines bus protocol at power-up
TS (6)	Timestamp input	Active-low tamper detection input with 200 kΩ internal pull-up; triggers timestamp capture on edge
CLKOUT (7)	Programmable clock output	Open-drain; configurable 1 Hz–32.768 kHz square wave for MCU/system clocking or calibration
VSS (8)	Ground	Primary ground reference for digital and analog sections
PFO (14)	Power fail output	Open-drain active-low signal indicating VDD drop below VBAT and threshold - used for system-level power sequencing
PFI (15)	Power fail input	External power-fail detection input; asserts PFO if pulled low while VDD is valid
RST (16)	Reset output	Open-drain watchdog reset signal; drives external MCU reset upon timeout unless masked
INT (17)	Interrupt output	Open-drain multi-source interrupt (alarm, timestamp, watchdog, countdown timer) - requires external pull-up
BBS (18)	Battery backed supply	Stable output voltage derived from VBAT during backup; powers internal logic and SRAM
VBAT (19)	Battery supply input	Accepts 1.2 V–4.2 V backup source; connects to VSS if battery backup is disabled
VDD (20)	Main supply input	Primary power rail (1.2 V–4.2 V); powers all functions except backup SRAM and RTC oscillator during switchover

Key Features

Feature	Design Value
Integrated TCXO + crystal	Eliminates external crystal and load capacitors - reduces BOM count and layout sensitivity while guaranteeing ±3 ppm accuracy
Timestamp with dual-event detection	Single TS pin captures two distinct tamper events (e.g., intermediate level + ground) - enables secure metering anti-tamper logging
Programmable aging offset	AO[3:0] register adjusts frequency by ±7 ppm at 25 °C - compensates long-term crystal drift without hardware replacement
Battery switch-over with timestamp	BTSE bit enables automatic time/date stamping at VDD-to-VBAT transition - preserves precise power-loss event timing for forensic analysis
Multi-function interrupt pin (INT)	Single open-drain output signals alarm, watchdog timeout, timestamp, or countdown completion - simplifies MCU GPIO usage
Power fail detection (PFI/PFO)	Dual-path monitoring: PFI accepts external fail signal; PFO asserts when internal VDD drops - enables robust system-level brown-out response

Applications

Smart Electricity Metering	GPS Time-to-First-Fix Acceleration
Use Scenario: Utility-grade electricity meter operating unattended for >10 years with tamper-resistant time-stamped billing logs. IC Role / Device Role / Timing Role: Primary RTC providing certified time-of-day, calendar, leap-year correction, and secure timestamping on physical intrusion (TS pin). Use Value: ±3 ppm accuracy ensures <1 s/month time error; battery-backed SRAM stores tariff schedules and consumption history across power outages.	Use Scenario: Portable GPS receiver requiring rapid satellite acquisition after cold start. IC Role / Device Role / Timing Role: High-stability timebase enabling almanac prediction and coarse time assistance - reducing TTFF from minutes to seconds. Use Value: Integrated TCXO eliminates external crystal calibration; CLKOUT at 16.384 kHz enables precise oscillator measurement for faster frequency lock.
Water/Gas Meter Data Logging	Industrial Process Timing Controller
Use Scenario: Battery-powered ultrasonic water meter recording flow intervals and leak events over 15-year field life. IC Role / Device Role / Timing Role: Low-power RTC managing scheduled sensor reads, storing timestamps in 512-byte SRAM, and triggering alarms on abnormal flow patterns. Use Value: 0.65 µA typical current extends CR2032 life beyond 10 years; timestamp function logs exact time of each tamper or maintenance event.	Use Scenario: Programmable logic controller (PLC) module requiring deterministic timing for batch process sequencing and safety interlocks. IC Role / Device Role / Timing Role: System timing supervisor generating 1-second interrupts, watchdog resets, and calibrated clock outputs for synchronized I/O scanning. Use Value: Programmable countdown timer and watchdog with reset capability ensure fail-safe shutdown if host MCU hangs; CLKOUT provides jitter-free system clock.

Smart Electricity Metering

GPS Time-to-First-Fix Acceleration

Use Scenario: Utility-grade electricity meter operating unattended for >10 years with tamper-resistant time-stamped billing logs.

IC Role / Device Role / Timing Role: Primary RTC providing certified time-of-day, calendar, leap-year correction, and secure timestamping on physical intrusion (TS pin).

Use Value: ±3 ppm accuracy ensures <1 s/month time error; battery-backed SRAM stores tariff schedules and consumption history across power outages.

Use Scenario: Portable GPS receiver requiring rapid satellite acquisition after cold start.

IC Role / Device Role / Timing Role: High-stability timebase enabling almanac prediction and coarse time assistance - reducing TTFF from minutes to seconds.

Use Value: Integrated TCXO eliminates external crystal calibration; CLKOUT at 16.384 kHz enables precise oscillator measurement for faster frequency lock.

Water/Gas Meter Data Logging

Industrial Process Timing Controller

Use Scenario: Battery-powered ultrasonic water meter recording flow intervals and leak events over 15-year field life.

IC Role / Device Role / Timing Role: Low-power RTC managing scheduled sensor reads, storing timestamps in 512-byte SRAM, and triggering alarms on abnormal flow patterns.

Use Value: 0.65 µA typical current extends CR2032 life beyond 10 years; timestamp function logs exact time of each tamper or maintenance event.

Use Scenario: Programmable logic controller (PLC) module requiring deterministic timing for batch process sequencing and safety interlocks.

IC Role / Device Role / Timing Role: System timing supervisor generating 1-second interrupts, watchdog resets, and calibrated clock outputs for synchronized I/O scanning.

Use Value: Programmable countdown timer and watchdog with reset capability ensure fail-safe shutdown if host MCU hangs; CLKOUT provides jitter-free system clock.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
PCF2127AT/2	Revised IC revision (Rev. 2 vs. Rev. 1); identical electrical specs and pinout; improved production yield and long-term reliability	No functional change; suitable for new designs where extended lifecycle support is required	Select PCF2127AT/2 for new designs per NXP's recommendation - same footprint, enhanced manufacturing maturity
PCF2129T/1,518	Higher accuracy (±2 ppm from −40 °C to +85 °C); adds internal temperature sensor readout register; same SO20 package and pin compatibility	Required for industrial environments exceeding −15 °C to +60 °C range or where on-die temperature telemetry is needed	Choose PCF2129T/1,518 when wider temperature range or direct temperature monitoring is mandatory - otherwise PCF2127AT/1,518 suffices

Compared with PCF2127AT/1,518, PCF2127AT/2 offers identical functionality with updated process control for longer product lifecycle, while PCF2129T/1,518 delivers tighter accuracy and thermal telemetry at the cost of higher unit price and marginally increased power - making PCF2127AT/1,518 optimal for cost-sensitive, commercial-temperature metering applications.

Availability

PCF2127AT/1,518 is available at Aetrix Electronics and suitable for electronic metering, precision timekeeping, and GPS equipment requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for PCF2127AT/1,518 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 specializing in secure connectivity solutions for automotive, industrial, and IoT applications, with deep expertise in mixed-signal timing and power management ICs.

The PCF2127AT/1,518 belongs to NXP's high-accuracy RTC product line, designed specifically for utility metering, portable navigation, and long-life battery-operated systems demanding sub-second monthly timekeeping stability without external compensation components.

FAQ

What is the primary timing accuracy specification for the PCF2127AT/1,518 over its operating temperature range?

The PCF2127AT/1,518 achieves ±3 ppm accuracy from −15 °C to +60 °C due to its integrated Temperature Compensated Crystal Oscillator (TCXO) and factory-calibrated load capacitance modulation. This specification is measured at the CLKOUT pin when configured to frequencies other than 32.768 kHz - such as 16.384 kHz - to avoid measurement artifacts. The PCF2127AT/1,518 maintains this accuracy without requiring external calibration or trimming components.

How does the PCF2127AT/1,518 handle power failure and battery backup switching?

The PCF2127AT/1,518 features an autonomous battery switch-over circuit that monitors VDD against VBAT and a programmable threshold (Vth(sw)bat ≈ 2.5 V). In standard mode, it switches to VBAT when VDD falls below both VBAT and the threshold; in direct mode, it switches as soon as VDD < VBAT. Upon switchover, the BF flag is set, INT is asserted (if enabled), and optional timestamp capture occurs - all while disabling the serial interface to prevent corruption. The PCF2127AT/1,518 continues accurate timekeeping using BBS-supplied power.

Can the PCF2127AT/1,518 operate with only a main supply and no backup battery?

Yes, the PCF2127AT/1,518 can operate without a backup battery. Configure PWRMNG[2:0] = 110 or 111 in Control_3 to disable battery switch-over, and connect VBAT to VSS. In this configuration, battery low detection and backup SRAM retention are disabled, but the RTC, calendar, alarms, timers, and interfaces remain fully functional as long as VDD is within 1.2 V–4.2 V. The PCF2127AT/1,518 retains full timing accuracy and feature set - only backup persistence is forfeited.

What interface protocols does the PCF2127AT/1,518 support, and how is bus selection implemented?

The PCF2127AT/1,518 supports both I²C Fast-mode (up to 400 kHz) and 3-wire SPI (up to 6.5 Mbit/s), selected at power-up via the IFS pin: connect IFS to VSS for SPI mode; connect IFS to BBS for I²C mode. SCL serves as the shared clock; SDA/CE functions as bidirectional I²C data or active-low SPI chip enable; SDI/SDO are dedicated SPI data lines. The PCF2127AT/1,518 does not support simultaneous dual-bus operation - selection is hardware-fixed at initialization.

Does the PCF2127AT/1,518 provide any mechanism to compensate for long-term crystal aging?

Yes, the PCF2127AT/1,518 includes an Aging_offset register (address 19h) with AO[3:0] bits enabling ±7 ppm frequency correction at 25 °C. Each AO value adjusts the TCXO's compensation point - for example, AO = 1001 applies −1 ppm, AO = 0111 applies +1 ppm - allowing field or production-line calibration to counteract crystal aging drift over years of operation. This correction is applied within the temperature compensation circuit and does not require external components or firmware recalibration loops. The PCF2127AT/1,518 uses this register to maintain long-term accuracy without hardware intervention.

PCF2127AT/1,518 Specifications

Product attributes: Attribute value

Manufacturer:: NXP Semiconductors

Series:: -

Package/Case:: 20-SOIC (0.295", 7.50mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Programmable:: Not Verified

Type:: Clock/Calendar

Features:: Alarm, Leap Year, Square Wave Output, SRAM, TCXO/Crystal, Watchdog Timer

Memory Size:: 512B

Time Format:: HH:MM:SS (12/24 hr)

Date Format:: YY-MM-DD-dd

Interface:: I2C, 2-Wire Serial

Voltage - Supply:: 1.8V ~ 4.2V

Voltage - Supply, Battery:: 1.8V ~ 4.2V

Current - Timekeeping (Max):: 1.5µA @ 3.3V

Operating Temperature:: -40°C ~ 85°C

Mounting Type:: Surface Mount

Grade:: -

Qualification:: -

Supplier Device Package:: 20-SO

PCF2127AT/1,518 FAQ

1.How can I place an order for PCF2127AT/1,518 through Aetrix?

Please submit a Request for Quotation (RFQ) for PCF2127AT/1,518 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for PCF2127AT/1,518 reliable?

The price and inventory of PCF2127AT/1,518 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for PCF2127AT/1,518 is usually 5 days.

3.What payment methods are accepted for PCF2127AT/1,518?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for PCF2127AT/1,518 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for PCF2127AT/1,518?

PCF2127AT/1,518 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your PCF2127AT/1,518 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for PCF2127AT/1,518?

For technical support, including PCF2127AT/1,518 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your PCF2127AT/1,518 requirements.

6.How does Aetrix verify that PCF2127AT/1,518 is sourced from the original manufacturer or authorized distributors?

All PCF2127AT/1,518 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that PCF2127AT/1,518 meets industry standards.

7.What is the process for return or replacement of PCF2127AT/1,518?

All PCF2127AT/1,518 units undergo pre-shipment inspection (PSI). If there is an issue with PCF2127AT/1,518, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The PCF2127AT/1,518 part is unused and in its original packaging.

Return procedure for PCF2127AT/1,518:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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