BR24A01AFJ-WM Ver la hoja de datos (PDF) - ROHM Semiconductor

Número de pieza

componentes Descripción

Fabricante

BR24A01AFJ-WM

105℃ Operation I2C BUS EEPROM (2-Wire)

ROHM Semiconductor 

BR24Axxx-WM (1K 2K 4K 8K 16K 32K 64K)

●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

Figure 51. I/O circuit diagram

Over current flows to SDA line by 'H'

output of microcontroller and 'L'

output of EEPROM.

Figure 52. Input / output collision timing

○Maximum value of Rs

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

(1)SDA 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.

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

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

VCC

RPU A

RS

IOL

Bus line

capacity CBUS

VOL

(VCC－VOL)×RS

RPU+RS

+ VOL+0.1VCC≦VIL

∴

RS

≦

VIL－VOL－0.1VCC

1.1VCC－VIL

×

RPU

Example）When VCC=3V,　VIL=0.3VCC,　VOL=0.4V,　RPU=20kΩ ,

VIL Microcontroller

EEPROM

Figure 53. I/O circuit diagram

from(2),

RS

≦

0.3×3－0.4－0.1×3

1.1×3－0.3×3

×

≦ 1.67［kΩ ］

20×103

○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.

RPU

RS

'L' output

'H' output

Over currentⅠ

Microcontroller

EEPROM

Figure 54. I/O circuit diagram

VCC ≦

RS

I

∴

RS

≧ VCC

I

Example）When VCC=3V, I=10mA

RS

≧

3

10×10-3

≧ 300［Ω ］

www.rohm.com

© 2012 ROHM Co., Ltd. All rights reserved.

TSZ22111・15・001

20/28

TSZ02201-0R1R0G100140-1-2

29.Jan.2018 Rev.003

Share Link: