BU9833GUL-W_10 Datasheet, PDF (14/19 Pages) Rohm – WL-CSP EEPROM family I2C BUS

BU9833GUL-W
Technical Note
●Cautions on microcontroller connection
○Rs
In I²C BUS, it is recommended that SDA port is of open drain input / output. However, when to use COMS input / output
of tri state to SDA port, insert a series resistance Rs between the pull up resistance R_PU and the SDA terminal of
EEPROM. This controls over protection of SDA terminal against surge. Therefore, even when SDA port is open drain
input / output, Rs can be used.
ACK
SCL
RPU
RS
SDA
“H” output of
microcontroller
“L” output of EEPROM
Microcontroller
EEPROM
Fig.48 I/O circuit diagram
Over current flows to SDA line by “H” output of
microcontroller and “L” output of EEPROM.
Fig.49 Input / output collision timing
○Maximum value of Rs
The maximum value of Rs is determined by the following relations.
(1) SDA rise time to be determined by the capacity (CBUS) of bus line of R_PU 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 RPU and Rs at the moment when EEPROM outputs “L” to SDA bus
should sufficiently secure the input “L” level (V_IL) of microcontroller including recommended noise margin 0.1V_CC.
VCC
RPU ^A
RS
VOL
IOL
Bus line
capacity CBUS
(VCC-VOL)×RS
RPU+RS
+ VOL+0.1VCC≦ VIL
∴ RS ≦
VIL-VOL-0.1VCC
1.1VCC-VIL
× RPU
Example) When VCC=3V, VIL=0.3VCC, VOL=0.4V, RPU=20kΩ,
VIL _{Microcontroller}
EEPROM
Fig.50 I/O circuit diagram
From (2)
RS ≦
0.3×3-0.4-0.1×3
1.1×3-0.3×3
×20×10³
≦ 1.67［kΩ］
○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 impedance of power source line
in set and so forth. Set the over current to EEPROM 10mA or below.
VCC
RS ^≦
I
RPU
RS
"L" output
RS
VCC
≧_I
"H" output
Over current I
Microcontroller
EEPROM
Fig.51 I/O Circuit diagram
Example) When Vcc =3V, I = 10mA,
RS
≧
3
10×10^-3
≧ 300［Ω］
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14/18
2010.10 - Rev.A