R2025S/D
duration of SDA and SCL pins are the half of bus operation duration. “× 2” in the numerator of the same member
is because there are two pins of SDA and SCL. The third member, (charging/discharging times per unit time)
means number of transition from “H” to “L” of the signal line.
Calculation example is shown below:
Pull-up resistor (Rp) = 10kΩ, Bus capacity = 50pF(both for SCL, SDA), VDD=3v,
In a system with sum of input current and off-state output current of each pin = 0.1µA,
I2C-Bus is used for 10ms every second while the rest of 990ms in the stand-by mode,
In this mode, number of transitions of the SCL pin from “H” to “L” state is 100 while SDA 50, every second.
Bus consumption current ≈
0.1µA×990msec
990msec + 10msec
+
3V × 10msec × 2
10KΩ × 2 × (990msec + 10msec)
+ 3V × 50pF × (100 + 50)
≈ 0.099µA + 3.0µA + 0.0225µA ≈ 3.12µA
Generally, the second member of the above formula is larger enough than the first and the third members bus
consumption current may be determined by the second member is many cases.
• Transmission System of I2C-Bus
(1) Start Condition and Stop Condition
In I2C-Bus, SDA must be kept at a certain state while SCL is at the “H” state during data transmission as shown
below.
SCL
SDA
tHD;DAT
tSU;DAT
The SCL and SDA pins are at the “H” level when no data transmission is made. Changing the SDA from “H” to
“L” when the SCL and the SDA are “H” activates the Start Condition and access is started. Changing the SDA from
“L” to “H” when the SCL is “H” activates Stop Condition and accessing stopped. Generation of Start and Stop
Conditions are always made by the master (see the figure below).
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RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
