Memory ICs
BR34L02FV-W
6) I/O circuit
• Pull up resister of SDA pin
The pull up resister is needed because SDA is NMOS open drain. Decide the value of this resister (RPU) properly,
by considering VIL, IL characteristics of a controller which control the device and VOH, IOL characteristics of the
device. If large RPU is chosen, clock frequency need to be slow.
In case of small RPU, the operating current increases.
• Maximum of RPU
Maximum of RPU is determined by following factor.
c SDA rise time determined by RPU and the capacitance of bus line (CBUS) must be less than TR.
And the other timing must keep the conditions of AC spec.
d When SDA bus is HIGH, the voltage A of SDA bus determined by a total input leak (IL) of the all devices
connected to the bus and RPU must be enough higher than input HIGH level of a controller and the device,
including noise margin 0.2VCC.
VCC − ILRPU − 0.2VCC ≥ VIH
RPU ≤
0.8VCC − VIH
IL
MICRO
COMPUTER
IL
RPU A
BR24LXX
SDA PIN
IL
Examples : When VCC=3V IL=10µA VIH=0.7VCC
According to 2
RPU ≤
0.8×3−0.7×3
10×10−6
≤ 300 [kΩ]
THE CAPACITANCE OF
BUS LINE (CBUS)
Rev.A 17/24