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BR24A Datasheet(PDF) 13 Page - Rohm

Part No. BR24A
Description  High Reliability Series EEPROMs I2C BUS
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Maker  ROHM [Rohm]
Homepage  http://www.rohm.com
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BR24A Datasheet(HTML) 13 Page - Rohm

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BR24A□□-WM series
Technical Note
13/17
www.rohm.com
2009.08 - Rev.C
© 2009 ROHM Co., Ltd. All rights reserved.
I/O peripheral circuit
Pull up resistance of SDA terminal
SDA is NMOS open drain, so requires pull up resistance. As for this resistance value (RPU), select an appropriate value to
this resistance value from microcontroller VIL, IL, and VOL-IOL characteristics of this IC. If RPU is large, action frequency is
limited. The smaller the RPU, the larger the consumption current at action.
Maximum value of RPU
The maximum value of RPU is determined by the following factors.
(1)SDA rise time to be determined by the capacitance (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 input leak total (IL) of device connected to bus at output of 'H' to SDA
bus and RPU should sufficiently secure the input 'H' level (VIH) of microcontroller and EEPROM including recommended
noise margin 0.2VCC.
Minimum value of RPU
The minimum value of RPU is determined by the following factors.
(1)When IC outputs LOW, it should be satisfied that VOLMAX=0.4V and IOLMAX=3mA.
(2)VOLMAX=0.4V should secure the input 'L' level (VIL) of microcontroller and EEPROM including recommended noise
margin 0.1VCC.
VOLMAX ≦ VIL-0.1 VCC
Ex. ) When VCC =3V, VOL=0.4V, IOL=3mA, microcontroller, EEPROM VIL=0.3VCC
from (1)
Therefore, the condition (2) is satisfied.
Pull up resistance of SCL terminal
When SCL control is made at CMOS output port, there is no need, but in the case there is timing where SCL becomes
'Hi-Z', add a pull up resistance. As for the pull up resistance, one of several kΩ ~ several ten kΩ is recommended in
consideration of drive performance of output port of microcontroller.
A0, A1, A2, WP process
Process of device address terminals (A0,A1,A2)
Check whether the set device address coincides with device address input sent from the master side or not, and select
one among plural devices connected to a same bus. Connect this terminal to pull up or pull down, or VCC or GND. And,
pins (N, C, PIN) not used as device address may be set to any of 'H' , 'L', and 'Hi-Z'.
Types with N.C.PIN
BR24A16/F/FJ -WM
A0, A1, A2
BR24A08/F/FJ-WM
A0, A1
BR24A04/F/FJ -WM
A0
Process of WP terminal
WP terminal is the terminal that prohibits and permits write in hardware manner. In 'H' status, only READ is available and
WRITE of all address is prohibited. In the case of 'L', both are available. In the case of use it as an ROM, it is
recommended to connect it to pull up or VCC. In the case to use both READ and WRITE, control WP terminal or connect it
to pull down or GND.
RPU
3-0.4
3×10
-3
867 [Ω]
And
VOL = 0.4 [V]
VIL = 0.3×3
= 0.9 [V]
RPU
Ex. ) When VCC =3V, IL=10μA, VIH=0.7 VCC,
from (2)
0.8×3- 0.7×3
10×10
-6
RPU
300 [kΩ]
0.8Vcc - VIH
IL
Vcc - ILRPU - 0.2Vcc ≧ VIH
VC-VOL
IOL
VCC-VOL
RPU
IOL
RPU
マイコン
RPU
A
BR24AXX
SDA terminal
IL
IL
バスライン容量
CBUS
Fig.51 I/O circuit diagram
Microcontroller
Bus line
capacity
CBUS


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