BR24G64NUX-5(2017) 데이터 시트보기 (PDF) - ROHM Semiconductor

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BR24G64NUX-5
(Rev.:2017)

Serial EEPROM Series Standard EEPROM I2C BUS EEPROM (2-Wire)

ROHM Semiconductor 

BR24G64xxx-5 Series

2. Cautions on Microcontroller Connection

(1) RS

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

tri state to SDA port, insert a series resistance RS between the pull-up resistor RPU and the SDA pin of EEPROM. This

is to control over current that may occur when PMOS of the microcontroller and NMOS of EEPROM are turned ON

simultaneously. RS also plays the role of protecting the SDA pin against surge. Therefore, even when SDA port is open

drain input/output, RS can be used.

VCC

ACK

SCL

RPU

RS

SDA

'HIGH' output of microcontroller

'LOW' output of EEPROM

Microcontroller

EEPROM

Figure 52. I/O Circuit Diagram

Over current flows to SDA line by 'HIGH'

output of microcontroller and 'LOW'

output of EEPROM.

Figure 53. I/O Collision Timing

(2) Maximum Value of RS

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

(a) SDA rise time to be determined by the capacitance (CBUS) of bus line of SDA and RPU should be tR or lower.

Furthermore, AC timing should be satisfied even when SDA rise time is slow.

○ (b) The bus electric potential A to be determined by RPU and RS when EEPROM outputs 'LOW' to SDA bus should

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

VCC

RPU A

RS

VOL

IOL

Bus line

capacitance

CBUS

VIL Microcontroller

EEPROM

Figure 54. I/O Circuit Diagram

(VCC -VOL)RS VOL 0.1VCC VIL

RPU  RS

∴RS

VIL -VOL -0.1VCC

1.1VCC -VIL

RPU

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

RS



0.3 3 -0.4 -0.1　3

1.1 3 -0.3 3

 20

10

3

 1.67 [ kΩ ]

(3) 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 the impedance of power

source line in set and so forth.

'HIGH'

output

VCC

RPU

RS

Over current I

'LOW'

output

Microcontroller

EEPROM

Figure 55. I/O Circuit Diagram

VCC  I

RS

Rs VCC

I

Ex.) VCC=3V I=10mA

Rs

3

 10 10

-3

300 [ Ω ]

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© 2017 ROHM Co., Ltd. All rights reserved.

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30.Nov.2017 Rev.001

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