Manual
BR24L32-W / BR24L32F-W / BR24L32FJ-W / BR24L32FV-W
Memory ICs
18/25
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 (R
PU
) properly,
by considering V
IL
, I
L
characteristics of a controller which control the device and V
OH
, I
OL
characteristics of the device.
If large R
PU
is chosen, clock frequency need to be slow. In case of small R
PU
, the operating current increases.
•
Maximum of R
PU
Maximum of R
PU
is determined by following factor.
c
SDA rise time determined by R
PU
and the capacitance of bus line (C
BUS
) must be less than T
R
.
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 (I
L
) of the all devices
connected
to the bus and R
PU
must be enough higher than input HIGH level of a controller and the device,
including noise margin 0.2V
CC
.
A
IL IL
MICRO
COMPUTER
BR24LXX
SDA PIN
R
PU
THE CAPACITANCE OF
BUS LINE (C
BUS)
V
CC
− I
L
R
PU
− 0.2V
CC
V
IH
R
PU
0.8V
CC
− V
IH
IL
R
PU
0.8×3−0.7×3
10×10
−6
300 [kΩ]
Examples : When V
CC
=3V I
L
=10µA V
IH
=0.7V
CC
According to
2
=
<
=
<
=
<
=
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