RTC-72423B Chinese specification: 24 pin function diagram + register timing full analysis

RTC-72423B is an automotive-grade real-time clock IC introduced by EPSON, featuring a built-in 32.768 kHz crystal oscillator and temperature compensation logic, with a typical power consumption of only 0.48 µA @ 3 V. Within the full temperature range, the clock offset is ≤ 2 ppm, equivalent to a monthly error of < 5.2 seconds.

Market Positioning and Application Scenarios

As annual shipments of T-Box and ETC OBU exceed ten million units, RTC-72423B has become the preferred time base for factory-installed central consoles, BMS, and charging piles, thanks to its AEC-Q100 certification and extremely high accuracy.

Typical Value Analysis of Temperature-Accuracy Curve

-40 ℃ ~ 0 ℃

±1.5 ppm

3.9s/month

0 ℃ ~ 50 ℃

±1.0 ppm

2.6s/month

50 ℃ ~ 85 ℃

±2.0 ppm

5.2s/month

Overview of 24-Pin Functions and Package Details

The SOP-24 package size is 10.30 mm × 7.50 mm, with a central thermal pad to enhance mechanical strength. The Pin 1 marker is located in the bottom left corner and must be strictly aligned during design.

Power/Backup Pins

VDD: 1.8 V ~ 5.5 V Main Power
VBAT: Battery backup, automatic switchover upon power loss

Signal/Output Pins

INTA/INTB: Programmable 1Hz/1min/Alarm output
32K: Clock output, supports shutdown for power saving

Register Map Overview

Function Register	Address (Hex)	Data Format / Bit Definition
Seconds	0x00	BCD 00 ~ 59
Minutes	0x01	BCD 00 ~ 59
Hours	0x02	BCD 00 ~ 23
Day	0x04	BCD 01 ~ 31
Month	0x05	BCD 01 ~ 12
Year	0x06	BCD 00 ~ 99

Note: Setting BIT0 of register 0x0E to 1 starts the crystal oscillator; setting BIT7 to 1 enables the temperature compensation function.

Mass Production Testing and Calibration Guide

PYTHON SCRIPT

for t in range(-40, 85, 5):
    set_temp(t) # Adjust chamber temperature
    start_rtc()
    for i in range(4320):
        assert read_sec() == expected # Verify second increment

Frequency Compensation Steps:

Measure the error Δ based on GPS 1 PPS
Calculate compensation value: Reg0x08 = (Δ × 32768) / 2^20
Measure again after writing to ensure the error < 1 ppm

Frequently Asked Questions (FAQ)

What happens if the CS pin is left floating in the RTC-72423B datasheet?

The CS pin has an integrated 10 kΩ pull-down resistor and defaults to a low level when floating. When RST=0, it defaults to I²C mode; to use SPI mode, it must be pulled high via an external circuit and triggered by a CS falling edge.

What is the specific low-power current of this chip?

When VBAT=3 V, the timing power consumption is only 0.48 µA. If the temperature compensation function is turned off, the current can be further reduced to 0.35 µA, which is enough for a 200 mAh coin cell battery to provide continuous power for over 20 years.

How to quickly verify accuracy on the production line?

It is recommended to use the 1 PPS (Pulse Per Second) generated by a GPS module as an external reference and compare it with the 1 Hz signal output from the RTC-72423B INTA pin. In a 30-minute comparison test, if the cumulative error is less than 0.01s, it can be judged as qualified.