BU9883FV-W Datasheet, PDF (15/19 Pages) Rohm – I2C BUS 3Ports for HDMI Port Serial EEPROM

●Cautions on microcontroller connection
○Rs
In I²C BUS, it is recommended that SDA port is of open drain input/output. However, when to use CMOS input / output of tri
state to SDA port, insert a series resistance Rs between the pull up resistance Rpu and the SDA terminal of EEPROM. This
is controls over current that occurs when PMOS of the microcontroller and NMOS of EEPROM are turned ON simultaneously.
Rs also plays the role of protection of SDA terminal against surge. Therefore, even when SDA port is open drain input/output,
Rs can be used. The following SCL SDA R_PU and R_S correspond to them of each port.
RPU
RS
SCL
SDA
'H' output of microcontroller
ACK
'L' output of EEPROM
Microcontroller
EEPROM
Fig.54 I/O circuit diagram
Over current flows to SDA line by 'H'
output of microcontroller and 'L'
output of EEPROM.
Fig.55 Input / output collision timing
○Maximum value of Rs
The maximum value of Rs is determined by the following relations. The following Vcc, V_OL, R_S, R_PU, I_OL, and SDA correspond to them
of each port.
(1)SDA rise time to be determined by the capacity (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.
(2)The bus electric potential A to be determined by Rpu and Rs the moment when EEPROM outputs 'L' to SDA bus should
sufficiently secure the input 'L' level (V_IL) of microcontroller including recommended noise margin 0.1Vcc.
VCC
RPU ^A
RS
IOL
Bus line
capacity CBUS
VOL
(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.56 I/O circuit diagram
from(2),
RS
≦
0.3×3－0.4－0.1×3
1.1×3－0.3×3
×
≦ 1.67［kΩ］
20×10³
○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. The following Vcc, R_PU, R_S, and I correspond to them of each port.
RPU
RS
'L' output
'H' output
Over currentⅠ
Microcontroller
EEPROM
Fig.57 I/O circuit diagram
15/18
VCC
RS
≦
I
∴
RS
≧
VCC
I
Example）When VCC=3V, I=10mA
RS
≧
3
10×10^-3
≧ 300［Ω］