BU9873 Datasheet, PDF (26/40 Pages) Rohm – I2C BUS Serial Interface RTC with High-precision Oscillation Adjustment

BU9873
Datasheet
• VOLMAX=0.4V should secure the input 'L' level (V_IL) of microcontroller and EEPROM,
including recommended noise margin 0.1Vcc.
VOLMAX ≤VIL ‐ 0.1VCC
Ex.) VCC =3V, VOL=0.4V, IOL=1mA, microcontroller, EEPROM V_IL=0.3Vcc
thus
∴RPU
≥
3 - 0.4
1×10 ^-3
≥ 2.6 kΩ
And VOL = 0.4 [V ]
VIL = 0.3 × 3
= 0.9 [V ]
Therefore, the second condition is also satisfied.
(2) Pull up resistance of SCL terminal
When SCL control is made at CMOS output port, there is no need for a pull up resistor. But when there is timing where
SCL becomes 'Hi-Z', add a pull up resistance. As for the pull up resistor value, one of several kΩ to several ten kΩ is
recommended in consideration of drive performance of output port of microcontroller.
3. Bypass Capacitor C₁ and C₂
When noise or surge gets in the power source line, malfunction may occur, therefore, for removing these, it is recommended
to attach bypass capacitors between IC V_DD and GND. Set bypass capacitors as close as possible to the IC, use a capacitor
for high frequency and another capacitor for low frequency in parallel. Recommended value for big capacitor C₂ is 0.1µF,
and small capacitor C₁ is several pF to hundreds of pF depending on the real application. And, it is also recommended to
attach a bypass capacitor between board V_DD and GND.
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