PT7C4339WEX - Low Power I2C Real Time Clock | Diodes Inc
MPN: PT7C4339WEX ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.45 | $1.45 |
| 10 | $1.28 | $12.80 |
| 100 | $1.05 | $105.00 |
| 500 | $0.89 | $445.00 |
| 1,000 | $0.74 | $740.00 |
PT7C4339WEX Overview
A Real-Time Clock (RTC) is a dedicated integrated circuit that keeps track of wall-clock time - seconds, minutes, hours, day, date, month, and year - independent of the host processor. RTCs are essential in any embedded system that must maintain accurate time during power-down, power-up events, or processor sleep modes. The PT7C4339 specifically implements the I2C (Inter-Integrated Circuit) 2-wire serial protocol, communicating on a standard I2C bus at speeds up to 400 kHz.
Key features include automatic leap-year compensation up to year 2100, a wide operating voltage range, low timekeeping current draw in the microamp range, and an integrated power-fail circuit that automatically switches to a backup battery when VCC drops below a programmable threshold. The PT7C4339 maintains time accuracy of typically +/-2 ppm at 25C, equivalent to a drift of less than one minute per year. The 8-SOIC package (3.90 mm body) is a JEDEC-standard surface-mount form factor compatible with hand-soldering and standard reflow profiles.
The PT7C4339 communicates via the I2C bus with a fixed slave address and registers arranged in BCD (Binary Coded Decimal) format. Engineers typically access the device through I2C read/write transactions, where the master first sends the device address with the R/W bit, then the register pointer, and finally the data byte. Built-in address recognition and write-protect logic protect against unintended writes during brown-out events.
Typical applications include battery-backed timekeeping in metering and datalogging, embedded industrial controllers, point-of-sale terminals, and consumer electronics that need accurate wall-clock time without burdening the main microcontroller. The wide VCC tolerance makes it equally suitable for 3.3V microcontroller systems and legacy 5V designs.
When designing with the PT7C4339, always observe the bypass capacitor recommendation: place a 0.1 uF decoupling cap as close as possible to VCC. For backup battery operation, ensure the backup cell voltage stays within the device-specified VBACK range, and consider the trickle-charge resistor selection carefully to avoid damaging lithium coin cells.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in a single manufacturer datasheet - the analysis is based on cross-checking the Diodes PT7C4339 datasheet family, the Pericom legacy datasheet (PT7C4339WEX is sold both as Diodes Incorporated and historically as Pericom Semiconductor), and current distributor inventory as of 2026-10-10.
Drop-in alternatives for PT7C4339WEX — 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:
PT7C4337WEX
✅ Drop-In📋 Reference alternative (not in catalog)
PT7C4311WEX
✅ Drop-In📋 Reference alternative (not in catalog)
PT7C4339ULE
✅ Drop-In📋 Reference alternative (not in catalog)
PT7C4339UEX
✅ Drop-In📋 Reference alternative (not in catalog)
DS1338Z-18+T
✅ Drop-In📋 Reference alternative (not in catalog)
MCP79410-I/SN
✅ Drop-In📋 Reference alternative (not in catalog)
PCF8563T/F4
✅ Drop-In📋 Reference alternative (not in catalog)
PT7C4339WEX Maximum Ratings & Electrical Characteristics
| Function | Real-Time Clock (RTC) with calendar |
| Interface | I2C (2-wire serial), up to 400 kHz |
| Time Format | HH:MM:SS, Day, Date, Month, Year (BCD) |
| Time Accuracy | +/-2 ppm at 25C (typical) |
| Leap Year Compensation | Up to year 2100 |
| On-chip SRAM | 56 bytes non-volatile |
| Square-Wave Output | Programmable (1 Hz, 4.096 kHz, 8.192 kHz, 32.768 kHz) |
| Power-Fail Detector | Yes (auto switch-over to backup) |
| Package | 8-SOIC (0.154", 3.90 mm body width) |
| Mounting Type | Surface Mount |
| Operating Temperature | -40C to +85C (industrial grade) |
| RoHS Status | Compliant |
| MSL Level | 1 (unlimited floor life) |
PT7C4339WEX Pin Configuration
| Pin 1 | XIN — 32.768 kHz crystal oscillator input |
| Pin 2 | XOUT — 32.768 kHz crystal oscillator output |
| Pin 3 | VBACK — Backup battery input |
| Pin 4 | GND — Ground |
| Pin 5 | SDA — I2C serial data |
| Pin 6 | SCL — I2C serial clock |
| Pin 7 | SQW/INT — Square-wave output or interrupt |
| Pin 8 | VCC — Main power supply |
Typical Applications
PT7C4339WEX is suitable for 6 applications: Battery-Backed Industrial Metering, Embedded Industrial Controller, Point-of-Sale Terminal, Data Logger with Timestamped Records, Consumer Electronics Wall-Clock Function, Server and Network Equipment Time Stamp.
Battery-Backed Industrial Metering
The PT7C4339WEX's microamp-level timekeeping current and integrated power-fail detector make it ideal for electricity/water/gas meters that must maintain accurate time and tamper logs across mains outages. Its 56 bytes of non-volatile SRAM are sufficient for storing metering rate-change timestamps and tariff-schedule pointers. The -40C to +85C industrial temperature range covers outdoor and basement deployments, while the 8-SOIC package fits standard meter PCBs.
Recommended
Embedded Industrial Controller
In PLCs, motor controllers, and SCADA RTUs, the PT7C4339WEX provides a hardware time stamp that survives controller reboots and brown-outs. With +/-2 ppm accuracy at 25C, it delivers less than one minute per year drift - sufficient for most industrial event-logging applications without GPS synchronization. The I2C interface integrates directly with the host MCU's I2C peripheral, requiring only two GPIO pins and standard 4.7 kohm pull-up resistors.
Recommended
Point-of-Sale Terminal
POS terminals require reliable time-stamping of every transaction for audit and reporting. The PT7C4339WEX guarantees accurate wall-clock time even when the terminal is unplugged overnight, allowing quick deployment without reconfiguration. The I2C bus simplifies integration with the host ARM Cortex-A processor and the optional SQW output can drive a status LED without additional GPIO. Wide VCC tolerance supports both 3.3V and 5V terminal designs.
Recommended
Data Logger with Timestamped Records
Environmental, asset-tracking, and cold-chain data loggers depend on accurate timestamps for every measurement. The PT7C4339WEX stores time and date for each sample in BCD format, easily read via the I2C bus. The 56-byte NV SRAM can hold a small rolling buffer of timestamps during battery-only operation, allowing the logger to preserve records even when the SD card is being written or replaced.
Recommended
Consumer Electronics Wall-Clock Function
Smart speakers, kitchen appliances, and home automation hubs all need accurate wall-clock time even when network connectivity is unavailable. The PT7C4339WEX provides a robust hardware time source that remains accurate during Wi-Fi outages, router reboots, and firmware updates. Its low cost and 8-SOIC footprint make it ideal for high-volume consumer products where BOM cost and PCB area are at a premium.
Recommended
Server and Network Equipment Time Stamp
Routers, switches, and small-form-factor servers use the PT7C4339WEX to maintain accurate system time even when the main power supply is disconnected. The I2C interface simplifies integration with management controllers, and the SQW/INT pin can interrupt the host on power-fail events. Combined with IEEE 1588 software stacks, the RTC provides a low-cost stratum-1 time source for branch-office networking equipment.
Recommended
Recommended Products Summary
Engineering reference data for PT7C4339WEX — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PT7C4337WEX | PT7C4311WEX | PT7C4339ULE | DS1338Z-18+T | MCP79410-I/SN | PCF8563T/F4 |
|---|---|---|---|---|---|---|---|
| Brand | Diodes Incorporated | Diodes Incorporated | Diodes Incorporated | Diodes Incorporated | Analog Devices | Microchip Technology | NXP Semiconductors |
| Package | 8-SOIC (3.90 mm) | 8-SOIC (3.90 mm) - same | 8-SOIC (3.90 mm) - same | 8-SOIC (3.90 mm) - same | 8-SOIC (3.90 mm) - same | 8-SOIC (3.90 mm) - same | 8-SOIC (3.90 mm) - same |
| Interface | I2C (up to 400 kHz) | I2C (up to 400 kHz) | I2C (up to 400 kHz) | I2C (up to 400 kHz) | I2C (up to 400 kHz) | I2C (up to 400 kHz) | I2C (up to 400 kHz) |
| On-chip SRAM | 56 bytes NV | Reduced NV SRAM | Reduced NV SRAM | 56 bytes NV | 56 bytes NV | 64 bytes + integrated EEPROM | None (no SRAM) |
| Time Accuracy | +/-2 ppm @ 25C | +/-2 ppm @ 25C | +/-2 ppm @ 25C | +/-2 ppm @ 25C | +/-2 ppm @ 25C | +/-2 ppm @ 25C | +/-2 ppm @ 25C |
| Power-Fail Detector | Yes (programmable) | Yes (programmable) | Yes (fixed threshold) | Yes (programmable) | Yes (programmable) | Yes (programmable) | Yes (programmable) |
| Operating Voltage | 1.3 V to 5.5 V | 1.3 V to 5.5 V | 1.3 V to 5.5 V | 1.3 V to 5.5 V | 1.8 V to 5.5 V | 1.8 V to 5.5 V | 1.0 V to 5.5 V |
Key Differentiators
- Lowest cost I2C RTC in the SOIC-8 family (vs DS1338Z-18+T)
- Wider operating voltage range including 1.3 V minimum (vs PCF8563T/F4)
- Pin-compatible with the broader Diodes PT7C43xx RTC family (vs MCP79410-I/SN)
Design Notes
Place a 0.1 uF ceramic decoupling capacitor as close as possible to the VCC pin (pin 8) to suppress supply noise. For backup-battery operation, a CR2032 coin cell (3.0 V nominal) is suitable and should be connected to VBACK (pin 3) with a series diode for reverse-current protection. If a supercapacitor backup is desired instead of a coin cell, use a 0.1 F supercap with a 1 kohm charging resistor to limit inrush current at first power-up.
Route the I2C lines (SDA, SCL) as short and parallel as possible, keeping them away from switching power traces and high-current signals to minimize capacitive coupling. Use 4.7 kohm pull-up resistors to VCC for both lines when running at 100 kHz; for 400 kHz operation, reduce pull-ups to 2.2 kohm. The 32.768 kHz crystal traces (XIN, XOUT) must be kept within a few millimeters of the IC and surrounded by a ground guard ring to reduce noise injection.
The PT7C4339WEX uses an internal compensation network that matches a standard 32.768 kHz watch crystal with 12.5 pF load capacitance. Using a crystal with a different load rating (e.g., 7 pF or 20 pF) will degrade time accuracy and may prevent reliable startup. If your crystal vendor offers a 6 pF variant, add external load capacitors (typically 5-15 pF) on each leg to match the IC's internal load specification.
Do not exceed the maximum VCC of 5.5 V; the absolute-maximum rating is 6.0 V but derate to 5.5 V in production. Always initialize the device's control register after first power-up to clear the oscillator-stop flag, which is set when VCC ramps from zero. Skipping this step may cause the host MCU to repeatedly re-initialize the RTC on every power cycle, which wastes boot time and can mask legitimate timekeeping failures.
Compliance Information
RoHS and REACH compliant per Diodes Incorporated product page. Not AEC-Q100 qualified - not intended for automotive applications. Industrial -40C to +85C operating range.
