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RV5C387A Datasheet(PDF) 23 Page - RICOH electronics devices division |
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RV5C387A Datasheet(HTML) 23 Page - RICOH electronics devices division |
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23 / 49 page  23 RV5C387A Cautions on Determining RP Resistance (1) Voltage drop at RP due to sum of input current or output current at off conditions on each IC pin connected to the I 2C bus shall be adequately small. (2) Rising time of each signal shall be kept short even when all capacity of the bus is driven. (3) Current consumed in I 2C bus is small compared to the consumption current permitted for the entire system. When all ICs connected to I 2C bus are CMOS type, condition (1) may usually be ignored since input current and off state output current is extremely small for the many CMOS type ICs. Thus the maximum resistance of RP may be determined based on (2) while the minimum on (3) in most cases. In actual cases a resistor may be place between the bus and input/output pins of each IC to improve noise margins in which case the RP minimum value may be determined by the resistance. Consumption current in the bus to review (3) above may be expressed by the formula below: Bus consumption current = (Sum of input current and off state output current of all devices in stand-by mode) × Bus stand-by duration Bus stand-by duration + bus operation duration + Supply voltage × bus operation duration × 2 RP resistance × 2 × (bus stand-by duration + bus operation duration) + supply voltage × bus capacity × charging/discharging times per unit time Operation of “ × 2” in the second member denominator in the above formula is derived from assumption that “L” 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)=10k Ω, Bus capacity=50pF (both for SCL and SDA), VDD=3V In as system with sum of input current and off state output current of each pin=0.1µA, I 2C bus is used for 10ms every second while the rest of 990ms is 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 × 990ms 990ms + 10ms + 3V × 10ms × 2 10k Ω × 2 × (990ms + 10ms) + 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 in many cases. . . |
Similar Part No. - RV5C387A_03 |
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Similar Description - RV5C387A_03 |
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