Datasheet
BR24G256-3
I/O Peripheral Circuit
1. Pull-up Resistance of SDA Terminal
SDA is NMOS open drain, so it requires a pull up resistor. As for this resistor value (RPU), select an appropriate value
from microcontroller VIL, IL, and VOL-IOL characteristics of this IC. If RPU is large, operating frequency is limited. The
smaller the RPU, the larger is the supply current (Read).
2. Maximum Value of RPU
The maximum value of RPU is determined by the following factors.
(1) SDA rise time to be determined by the capacitance (CBUS) of bus line and RPU of SDA should be tR or lower.
Furthermore, AC timing should be satisfied even when SDA rise time is slow.
(2) The bus electric potential
A to be determined by input current leak total (IL) of the device connected to the bus with
○
output of 'H' to SDA line and RPU should sufficiently secure the input 'H' level (VIH) of microcontroller and EEPROM
including recommended noise margin of 0.2Vcc.
Microcontroller
BR24GXX
VCC-ILRPU-0.2 VCC ≧ VIH
0.8VCC－VIH
RPU
∴
RPU≦
IL
SDA terminal
A
Ex.) VCC =3V IL=10µA VIH=0.7 VCC
from (2)
IL
IL
0.8×3－0.7×3
RPU≦
10×10-6
Bus line
Capacity
CBUS
≦ 30 [kΩ]
Figure 44. I/O Circuit Diagram
3. Minimum Value of RPU
The minimum value of RPU is determined by the following factors.
(1) When IC outputs LOW, it should be satisfied that VOLMAX=0.4V and IOLMAX=3mA.
VCC-VOL
≦IOL
RPU
VCC－VOL
∴
RPU≧
IOL
(2) VOLMAX=0.4V should secure the input 'L' level (VIL) of microcontroller and EEPROM including recommended noise
margin 0.1VCC
.
VOLMAX ≦ VIL-0.1 VCC
Ex.) VCC =3V, VOL=0.4V, IOL=3mA, microcontroller, EEPROM VIL=0.3Vcc
from (1)
3－0.4
3×10－
RPU≧
3
≧
867[Ω]
And
VOL=0.4 [V]
VIL=0.3×3
=0.9 [V]
Therefore, the condition (2) is satisfied.
4. Pull-up Resistance of SCL Terminal
When SCL control is made at the CMOS output port, there is no need for a pull up resistor. But when there is a time
where SCL becomes 'Hi-Z', add a pull up resistor. 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.
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