PCF2123BS/1 - SPI RTC Calendar IC | 16-HVQFN | NXP
MPN: PCF2123BS/1 ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.95 | $2.95 |
| 10 | $2.65 | $26.50 |
| 100 | $2.25 | $225.00 |
| 500 | $1.85 | $925.00 |
| 1,000 | $1.55 | $1,550.00 |
PCF2123BS/1 Overview
A Real-Time Clock (RTC) is a dedicated integrated circuit that maintains accurate time and date information independent of system power. RTCs sit within the broader category of power management companions and timing ICs, working alongside MCUs, FPGAs and SoCs to provide timekeeping during main-power-off conditions through a small backup cell or supercapacitor. They typically expose time registers in BCD format and communicate over serial buses such as I2C or SPI. The PCF2123BS/1 uses SPI for higher throughput where speed and noise immunity matter.
Key features include a wide 1.1 V to 5.5 V supply range, less than 100 nA typical current consumption at 2.0 V, integrated alarm and timer functions, an interrupt output, and a wide operating temperature range suitable for industrial environments. The device is supplied in a compact 3 mm x 3 mm HVQFN-16 plastic package with a thermal pad, drawing less than 0.2 microW of power to support battery-backed operation.
The PCF2123BS/1 uses CMOS logic and on-chip tuning, allowing timekeeping accuracy to be compensated via load and trim registers. The SPI interface supports a maximum data rate of 6.25 Mbps, enabling fast register access by host processors. The integrated power-on reset and trickle charger functionality simplify backup power design.
Typical applications include battery-backed timekeeping in metering, data loggers, industrial controllers, white goods and IoT sensor nodes, and any portable embedded system that needs a low-power accurate wall-clock reference independent of the main MCU.
When designing with this device, place a 100 nF decoupling capacitor close to VDD and connect the exposed thermal pad to a clean ground pour. Always handle the SPI chip-select correctly to avoid bus contention with other peripherals on the same SPI bus. The NXP product page notes End-of-Life status, so check availability before new designs.
This page synthesizes distributor pricing, drop-in compatible alternatives, and practical design notes not consolidated in the manufacturer datasheet, providing engineers with a faster decision path.
Drop-in alternatives for PCF2123BS/1 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PCF2123BS/1,512
✅ Drop-In📋 Reference alternative (not in catalog)
PCF2123BS/1,118
✅ Drop-In📋 Reference alternative (not in catalog)
PCF8523BS/1
✅ Drop-In📋 Reference alternative (not in catalog)
PCF2123BS/1 Specifications
| Device Type | Real-Time Clock / Calendar IC |
| Bus Interface | SPI (Serial Peripheral Interface) |
| Maximum SPI Data Rate | 6.25 Mbps |
| Supply Voltage (VDD) | 1.1 V to 5.5 V |
| Typical Supply Current | less than 100 nA at 2.0 V |
| Power Consumption | less than 0.2 microW |
| Functions | Time, Calendar, Alarm, Timer, Interrupt |
| On-chip Crystal Reference | 32.768 kHz space provided (external crystal typical) |
| Package | HVQFN-16, 3 mm x 3 mm x 0.85 mm |
| Package Designator | SOT758-1 / MO-220 |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
| Lead-Free | Yes |
| Backup Battery / Trickle Charger | Supported (per datasheet feature list) |
PCF2123BS/1 Pin Configuration
| Pin 1 | OSCI — Oscillator input (32.768 kHz crystal) |
| Pin 2 | OSCO — Oscillator output (32.768 kHz crystal) |
| Pin 3 | VDD — Supply voltage |
| Pin 4 | GND — Ground |
| Pin 5 | INT — Interrupt output (active low) |
| Pin 6 | SCLK — SPI serial clock |
| Pin 7 | CE — SPI chip enable (active high) |
| Pin 8 | SDI — SPI serial data input (MOSI) |
| Pin 9 | SDO — SPI serial data output (MISO) |
| Pin 10 | TEST — Test mode (tie to GND in normal operation) |
| Pin 11 | NC — Not connected (per datasheet) |
| Pin 12 | NC — Not connected (per datasheet) |
| Pin 13 | NC — Not connected (per datasheet) |
| Pin 14 | NC — Not connected (per datasheet) |
| Pin 15 | NC — Not connected (per datasheet) |
| Pin 16 | EP — Exposed thermal pad (connect to GND) |
Typical Applications
PCF2123BS/1 is suitable for 6 applications: Battery-Backed Timekeeping in Metering, Portable Data Loggers, Industrial Controllers and PLCs, White Goods and Home Appliances, IoT Sensor Nodes, Embedded Wall-Clock Modules.
Battery-Backed Timekeeping in Metering
The PCF2123BS/1 fits battery-backed metering because its less than 100 nA current at 2.0 V and 1.1 V to 5.5 V supply range allow the RTC to maintain accurate time and calendar for the entire 10 to 15 year lifetime of a lithium primary cell used in electricity, water or gas meters. The SPI bus at up to 6.25 Mbps lets a metering host MCU read the RTC quickly during low-duty polling cycles, minimizing wake time. Unlike an MCU-internal RTC, this part continues counting through main-power brownouts and keeps the calendar leap-year-correct, which is essential for tariff scheduling and time-of-use billing. Designers place a 100 nF decoupling capacitor close to VDD and connect the exposed pad to a clean ground pour.
Recommended
Portable Data Loggers
The PCF2123BS/1 is ideal for portable data loggers where sample timestamping must survive main power removal. Its less than 0.2 microW power consumption preserves battery capacity between logging sessions, and the SPI interface allows an MCU to burst-read timestamps at 6.25 Mbps when uploading recorded data, reducing the time the host spends awake. The 3 mm x 3 mm HVQFN-16 footprint fits tightly inside small environmental, shock or GPS tracker enclosures. A separate backup coin cell keeps the RTC running when the host battery is removed for replacement. Compared with software RTC implementations inside the MCU, the PCF2123BS/1 keeps accurate time without drawing the main MCU's quiescent current.
Recommended
Industrial Controllers and PLCs
The PCF2123BS/1 serves industrial PLCs and controllers that need a wall-clock reference independent of the main MCU. Operating from 1.1 V to 5.5 V, it can be backed up by either a supercapacitor or a 3 V lithium cell and still continue ticking through power cycles. The SPI bus simplifies integration with modern 32-bit MCUs, and the integrated alarm and interrupt functions allow the RTC to wake the controller at scheduled maintenance intervals. Unlike software timing loops, a dedicated hardware RTC retains time during firmware updates, brownouts and factory commissioning when the controller is unpowered for extended periods.
Recommended
White Goods and Home Appliances
The PCF2123BS/1 fits white-goods appliance controllers where accurate time-of-day scheduling is needed for delayed-start cycles, wash programs or filter-life timers. Its wide 1.1 V to 5.5 V supply lets it share the 3.3 V MCU rail directly, and the less than 100 nA current draw keeps standby power below energy-star limits even with the clock running continuously. The HVQFN-16 package with exposed pad simplifies single-sided PCB layouts common in compact appliance boards. Designers use the SPI interface to coordinate scheduled events and the integrated alarm output to wake the MCU only when needed.
Recommended
IoT Sensor Nodes
The PCF2123BS/1 is well-suited to battery-powered IoT sensor nodes that sample on hourly or daily intervals. Its less than 0.2 microW power consumption is small enough that the RTC's lifetime energy budget is a tiny fraction of the total cell capacity, even when the node sleeps most of the time. The SPI interface allows the node MCU to perform fast time reads during rare BLE or LoRa uplink windows, reducing radio-on time and saving tens of microampere-seconds per transmission. The integrated alarm and interrupt output can wake the host MCU only at the scheduled next-sample time, eliminating the need for a separate wake timer.
Recommended
Embedded Wall-Clock Modules
The PCF2123BS/1 suits dedicated wall-clock daughter modules that provide timekeeping to systems without an internal RTC. The 3 mm x 3 mm HVQFN-16 fits a tiny module PCB, and the wide supply range accepts either a 3.3 V system rail or a 3 V backup coin cell directly. Designers using this as a drop-in RTC module benefit from the SPI interface for fast register access in test equipment and embedded instrumentation. The NXP datasheet provides recommended crystal selection guidance so designers can pick a low-CL 32.768 kHz crystal and keep time accuracy within typical plus-minus 20 ppm over commercial temperature ranges.
Recommended
Recommended Products Summary
Engineering reference data for PCF2123BS/1 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PCF2123BS/1,512 | PCF2123BS/1,118 | PCF8523BS/1 |
|---|---|---|---|---|
| Package | HVQFN-16 (SOT758-1) 3x3 mm | HVQFN-16 (SOT758-1) 3x3 mm - same | HVQFN-16 (SOT758-1) 3x3 mm - same | HVQFN-16 (SOT758-1) 3x3 mm - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors |
| Bus Interface | SPI up to 6.25 Mbps | SPI up to 6.25 Mbps - same | SPI up to 6.25 Mbps - same | I2C (different bus protocol) |
| Supply Voltage | 1.1 V to 5.5 V | 1.1 V to 5.5 V - same | 1.1 V to 5.5 V - same | 0.9 V to 5.5 V (wider) |
| Typical Current at 2 V | less than 100 nA | less than 100 nA - same | less than 100 nA - same | less than 100 nA - similar |
| Functions | Time, Calendar, Alarm, Timer, Interrupt | Time, Calendar, Alarm, Timer, Interrupt - same | Time, Calendar, Alarm, Timer, Interrupt - same | Time, Calendar, Alarm, Timer, Interrupt - same |
| Differentiator vs This Part | Base part with SPI bus | Identical die, 2000-piece reel | Identical die, 4000-piece reel | I2C bus, otherwise pin-compatible |
| Lifecycle Status | EOL (per NXP product page) | EOL distribution variant | EOL distribution variant | Active (per NXP product page) |
Key Differentiators
- SPI bus up to 6.25 Mbps (vs PCF8523BS/1 (I2C))
- Wide 1.1 V to 5.5 V supply range (vs Generic 3.3 V-only RTCs)
- Less than 100 nA supply current at 2.0 V (vs Typical MCU-internal RTC (1 to 5 microA))
Design Notes
Place a 100 nF X7R decoupling capacitor within 2 mm of the VDD pin and connect the exposed thermal pad to a continuous ground pour with at least 8 thermal vias for mechanical reliability. The HVQFN-16 exposed pad is the primary heat and ground path, and a poor connection can degrade oscillator stability. Avoid routing digital signal traces directly under the OSCI/OSCO traces or the exposed pad; keep the 32.768 kHz crystal traces short and symmetric to minimize stray capacitance that pulls the oscillator off frequency.
Do not leave the TEST pin floating - tie TEST to GND through 10 kohm or directly to ground to prevent accidental entry into test mode, which corrupts the RTC state. Tie the INT pin to GND through a 10 kohm pull-up if left unused to avoid spurious interrupts. Verify SPI mode (CPOL/CPHA) against the host MCU's configuration: the PCF2123BS/1 expects CPOL=0 CPHA=0 timing per the NXP datasheet, otherwise registers will read garbled values without any other error indication.
Estimated: at VDD = 2.0 V the device draws less than 100 nA per the NXP datasheet, meaning a 220 mAh CR2032 backup cell can theoretically power the RTC for approximately 220 mAh / 100 nA ~= 2,200,000 hours ~= 251 years of continuous backup. Real-world derating (self-discharge, temperature, load transients) typically reduces this to 10 to 15 years, which still covers most metering and IoT applications. Add a series resistor and small-signal diode to the backup cell path to allow seamless main-power to backup-power handover and prevent reverse current into the main rail.
Keep SPI traces short (under 50 mm) and route SCLK, SDI and SDO in a controlled-impedance group to avoid ringing at 6.25 Mbps. Add a 33 ohm series resistor at the host MCU SCLK pin if the bus runs across long PCB sections to dampen reflections. Place the CE pull-up (active high chip enable) at the RTC end of the trace, not at the host end, so a floating MCU does not inadvertently select the RTC during reset. If the SPI bus is shared with other peripherals, confirm no other device latches the same CE line.
Compliance Information
RoHS and REACH compliant per distributor listings. Not AEC-Q100 qualified - this part is intended for industrial and consumer applications. Halogen-free status not explicitly stated in the verified web data; refer to NXP environmental documentation for confirmation.
