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BR24T16FJ-WZE2

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

ROHM Semiconductor 

BR24T16-W

Datasheet

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 terminal 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 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 45. I/O Circuit Diagram

Over current flows to SDA line by 'H'

output of microcontroller and 'L'

output of EEPROM.

Figure 46. Input / Output Collision Timing

2. Maximum Value of RS

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

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

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

○ (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 of 0.1Vcc.

VCC

RPU A

RS

VOL

IOL

Bus line

capacity

CBUS

VIL Micro controller

EEPROM

Figure 47. I/O Circuit Diagram

(Vcc - VOL) ×

RPU+RS

RS

+VOL+0.1Vcc

≤

VIL

∴ 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 × 103

≤ 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. Set the over current to EEPROM at 10mA or lower.

'H' output

RPU

RS

'L'output

Over current I

Vcc

RS

≤I

Vcc

∴ RS ≥ I

EX) VCC=3V I=10mA

RS ≥

3

10 × 10-3

Microcontroller

EEPROM

Figure 48. I/O Circuit Diagram

≥ 300 [Ω]

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

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TSZ02201-0R2R0G100110-1-2

24.Dec.2020 Rev.008

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