●THE NOTICE ABOUT THE CONNECTION OF CONTROLLER
○ABOUT Rs
The open drain interface is recommended for SDA port in I2CBUS. But, in the case that Tri-state CMOS interface is applied
to SDA, insert a series resistor Rs between SDA pin of the device and a pull up resistor RPU. It limits the current from
PMOS of controller to NMOS of EEPROM.
Rs also protects SDA pin from surges. Therefore, Rs is able to be used though SDA port is open drain.
ACK
RPU
RS
SCL
SDA
'H'OUTPUT OF
CONTROLLER
“L” OUTPUT OF EEPROM
CONTROLLER
EEPROM
Fig.44 I/O CIRCUIT
The “H” output of controller
and the “L” output of EEPROM may
cause current overload to SDA line.
Fig.45 INPUT/OUTPUT COLLISION TIMING
○THE MAXIMUM VALUE OF Rs
The maximum value of Rs is determined by following factors.
①SDA rise time determined by RPU and the capacitance of bus line(CBUS) of SDA must be less than tR. And the other
timing must also keep the conditions of the AC timing.
②When the device outputs LOW on SDA line, the voltage of the bus A determined by RPU and Rs must be lower
than the inputs LOW level of the controller, including recommended noise margin(0.1VCC).
VCC
RPU A
RS
IOL
BUS
CAPACITANCE
VOL
(VCC-VOL)×RS
RPU+RS
+ VOL+0.1VCC≦VIL
∴ RS ≦
VIL-VOL-0.1VCC
1.1VCC-VIL
×
RPU
Examples : When VCC=3V VIL=0.3VCC VOL=0.4V RPU=20kΩ
VIL CONTROLLER
EEPROM
Fig.46 I/O CIRCUIT
According to ② RS ≦
0.3×3-0.4-0.1×3
1.1×3-0.3×3
×
≦ 1.67[kΩ]
20×103
○THE MINIMUM VALUE OF Rs
The minimum value of Rs is determined by the current overload due to the conflict on the bus.
The current overload may cause noises on the power line and instantaneous power down.
The following conditions must be met, where I is the maximum permissible current.
The maximum permissible current depends on Vcc line impedance and so on. It need to be less than 10mA for
EEPROM.
Vcc ≦ I
RS
"H" OUTPUT
RPU
RS
"L" OUTPUT
MAXIMUM
CURRENT
∴
RS
≧
Vcc
I
Examples: When VCC=3V, I=10mA
RS
≧
3
10×10-3
≧ 300[Ω]
CONTROLLER
EEPROM
Fig.47 I/O CIRCUIT
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