BR24T1MFJ-3AM 查看數據表（PDF） - ROHM Semiconductor
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BR24T1MFJ-3AM Datasheet PDF : 32 Pages
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BR24T1M-3AM
Datasheet
I/O Peripheral Circuit
1. Pull Up Resistance of SDA Terminal
SDA is NMOS open drain, so it requires a pull up resistor. As for this resistor value (RPU), select an appropriate value
from microcontroller VIL, IL, and VOL-IOL characteristics of this IC. If RPU is large, operating frequency is limited. The
smaller the RPU, the larger is the supply current (Read).
2. 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 SDA and RPU should be tR or lower.
Furthermore, 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 of 0.2VCC.
VCC-ILRPU-0.2 VCC ≧ VIH
∴
RPU
≦
0.8VCC－VIH
IL
Ex.) VCC =3V IL=10μA VIH=0.7 VCC
From (2)
Microcontroller
RPU
A
BR24TXX
SDA terminal
≦ 30 [kΩ]
IL
IL
Bus line
capacity
CBUS
3. Minimum Value of RPU
Figure 45. I/O Circuit Diagram
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.
VCC－VOL
RPU
≦
IOL
∴
RPU
≧
VCC－VOL
IOL
(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.) VCC =3V, VOL=0.4V, IOL=3mA, microcontroller, EEPROM VIL=0.3VCC
from (1)
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.
4. Pull Up Resistance of SCL Terminal
When SCL control is made at the CMOS output port, there is no need for a pull up resistor. But when there is a time
where SCL becomes 'Hi-Z', add a pull up resistor. As for the pull up resistor value, one of several kΩ to several ten kΩ is
recommended in consideration of drive performance of output port of microcontroller.
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TSZ22111・15・001
20/28
TSZ02201-0GFG0G100430-1-2
08.Jul.2016 Rev.001
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