What is "RTC"?

"RTC" is an acronym for Real Time Clock, which is an electronic device that measures time.

Are You Struggling with These Problems? 3 Types of Issues for In-vehicle Equipment

1. Accuracy of clock gets worse under high temperature conditions...

   Due to the increasing functionality of ADAS and autonomous driving, high power SOC with self-heating may significantly elevate the temperature inside the module. In addition, ECU are often installed in high temperature environments (e.g. near the battery).
   The 32kHz crystal that is typically used for the clock has a frequency characteristic that shift dramatically with temperature. This frequency shift causes significant the deviation of the time information.

2. Back up current consumption cannot meet specifications...

   The number of ECUs installed in cars is increasing and have become multifunctional. From this trend, the current consumption during standby mode is also increasing, and to reduce the current consumption of each ECUs is becoming more important year by year.
   Requirement of reducing current consumption is strong especially for the ECUs that continue to operate when the vehicle is turned off (e.g. BMS, Battery Management System).

3. Redundancy of the system is mandatory to improve safety of equipment...

   Redundancy of systems and parts is required are increasing to meet ISO 26262 requirements.
   Material costs and mounting space have become issues to accommodate high ASIL levels.

Epson RTC Module Solves 3 Types of Issues

Automotive and high accuracy RTC module RA4000CE and RA8000CE

It is a RTC module with enhanced features which AEC-Q100 qualified and can operate under a high temperature condition (up to 125°C). RA4000CE supports SPI-Bus interface and RA8000CE supports I²C-Bus interface.

Main features of RA4000CE and RA8000CE

• High accuracy time information under a high temperature condition up to 125°C.

  This product ensure the high accuracy clock during the temperature range from -40°C to 125°C due to the D-TCXO function.

• Automotive grade quality AEC-Q100.

  High automotive quality standard in all processes. (e.g. Design, Manufacturing, Process Control)

• Reduced current consumption during system standby mode.

  Low current consumption (300nA Typ.)

• Contribute to system redundancies and BoM reduction

  This product has many optional functions (e.g. reset function, time stamp function etc.)

• Available to choose the best one from many options and interfaced (I²C-Bus/SPI-Bus).

  This product support I²C-Bus interface and each SPI-Bus interfaces. Also supports various configuration of multiple event pins, time stamps, and other functions.

* Applications

- BMS (Battery Management System)
- Vehicle computer
- Central gateway
- Industrial machine

3 Reasons for Using RTC Module

1. Provide High precision time information when the temperature changes

   DTCXO (Digital Temperature Compensated Xtal Oscillator) is installed in the RTC module. The RTC module provides highly accurate time information up to 125°C when the temperature on the customer's board changes.

   Frequency Temperature Characteristics

   

   Comparison of Time Deviation

   Temperature		Existing product (no DTCXO)	RA8000CE RA4000CE
   85℃	Day	10.8s	0.5s
   	Month	5min 27s	13.2s
   105℃	Day	19.3s	0.7s
   	Month	9min 41s	21s
   125℃	Day	31s	4.4s
   	Month	15min 7s	2min 12s

2. Lowers overall system powe

   RTC module can keep the time information with one order of magnitude lower current consumption than the sleep mode of the MCU.RTC module can significantly reduce the power of the customer's system.

   

3. A reset function contributes to system redundancy

   RTC module detects a drop of the main power supply, and outputs a reset signal to the MCU. This eliminates the need for an external reset IC, which reduces the customer's board space, number of mounted parts, and cost. In addition, Customers who use only the reset function in the MCU can add redundancy to their system by using RTC module reset function.

   Common circuit configuration

   

   Epson proposal