BR24G04-3A
Datasheet
●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 supply current.
○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
Microcontroller
RPU
A
EEPROM
SDA terminal
RPU
≦
0.8×3-0.7×3
10×10-6
IL
IL
≦ 30 [kΩ]
Bus line
capacity
CBUS
Figure 45. 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
RPU
≦
IOL
∴
RPU
≧
VCC-VOL
IOL
②VOLMAX=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.) 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 to several ten kΩ is recommended in
consideration of drive performance of output port of microcontroller.
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