BR24T1MFJ-WE2_ 데이터 시트보기 (PDF) - ROHM Semiconductor

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BR24T1MFJ-WE2_

High Reliability Serial EEPROMs I2C BUS BR24□□□□ family

ROHM Semiconductor 

BR24T□□□□Series

Technical Note

●Cautions on microcontroller connection

○RS

In I2C BUS, it is recommended that SDA port is of open drain input/output. However, when to use CMOS input / output of

tri state to SDA port, insert a series resistance Rs between the pull up resistance Rpu and the SDA terminal of EEPROM.

This is controls over current that occurs when PMOS of the microcontroller and NMOS of EEPROM are turned ON

simultaneously. Rs also plays the role of protection of SDA terminal against surge. Therefore, even when SDA port is

open drain input/output, Rs can be used.

ACK

RPU

RS

SCL

SDA

'H' output of microcontroller

'L' output of EEPROM

Microcontroller

EEPROM

Fig.53 I/O circuit diagram

Over current flows to SDA line by 'H'

output of microcontroller and 'L'

output of EEPROM.

Fig.54 Input / output collision timing

○Maximum value of Rs

The maximum value of Rs is determined by the following relations.

①SDA rise time to be determined by the capacity (CBUS) of bus line of Rpu and SDA should be tR or below.

And AC timing should be satisfied even when SDA rise time is late.

②The bus electric potential ○A to be determined by Rpu and Rs the moment when EEPROM outputs 'L' to SDA bus

sufficiently secure the input 'L' level (VIL) of microcontroller including recommended noise margin 0.1Vcc.

VCC

RPU A

RS

IOL

Bus line

capacity

CBUS

VIL Micro controller

VOL

EEPROM

  VCC  VOL  VOL  0.1VCC  VIL

RPU  RS

 RS  VCC  VOL  RPU

1.1VCC  VIL

Ex)VCC=3V VIL=0.3VCC VOL=0.4V RPU=20kΩ

RS  0.3  3  0.4  0.1 3  20 103

1.1 3  0.3  3

Fig.55 I/O Circuit Diagram

 1.67[kΩ]

○Minimum value of Rs

The minimum value of Rs is determined by over current at bus collision. When over current flows, noises in power source

line, and instantaneous power failure of power source may occur. When allowable over current is defined as I, the

following relation must be satisfied. Determine the allowable current in consideration of impedance of power source line

in set and so forth. Set the over current to EEPROM 10mA or below.

'H' output

RPU

RS

'L'output

Over current I

Microcontroller

EEPROM

Fig.56 I/O circuit diagram

VCC  I

RS

 RS  VCC

I

EX) VCC=3V I=1mA

RS



3

10 103

 300 [Ω]

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© 2011 ROHM Co., Ltd. All rights reserved.

15/21

2011.03 - Rev.A

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