BR24T04FVJ-WG_ データシートの表示（PDF） - ROHM Semiconductor
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BR24T04FVJ-WG_ Datasheet PDF : 22 Pages
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BR24T□□□□Series
Technical Note
●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.
①SDA 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.
②The 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.
VCC－ILRPU－0.2 VCC ≧ VIH
RPU 0.8VCC VIH
IL
Ex.) VCC =3V IL=10µA VIH=0.7 VCC
from②
RPU
0.8 3 0.7 3
10 106
300 [kΩ]
Microcontroller
RPU
A
BR24TXX
SDA terminal
IL
IL
Bus line
capacity
CBUS
Fig.52 I/O circuit diagram
○ Minimum value of RPU
The minimum value of RPU is determined by the following factors.
When IC outputs LOW, it should be satisfied that VOLMAX=0.4V and IOLMAX=3mA.
VCC VOL IOL
RPU
RPU VCC VOL
IOL
②VOLMAX= should secure the input 'L' level (VIL) of microcontroller and EEPROM
including recommended noise margin 0.1Vcc.
VOLMAX ≦ VIL－0.1 VCC
Ex.) VCC =3V, VOL=0.4V, IOL=3mA, microcontroller, EEPROM VIL=0.3Vcc
from① RPU
3 0.4
3 10 3
867[Ω]
And VOL=0.4［V］
VIL=0.3×3
=0.9［V］
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.
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© 2011 ROHM Co., Ltd. All rights reserved.
14/21
2011.03 - Rev.A
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