LE2432RDXA
www.onsemi.com
14
Application Notes
1) Software reset function
Software reset (start condition + 9 dummy clock cycles + start condition), shown in the figure below, is
executed in order to avoid erroneous operation after power-on and to reset while the command input
sequence. During the dummy clock input period, the SDA bus must be opened (set to high by a pull-up
resistor). Since it is possible for the ACK output and read data to be output from the EEPROM during
the dummy clock period, forcibly entering H will result in an overcurrent flow.
Note that this software reset function does not work during the internal write cycle.
2) Pull-up resistor of SDA pin
Due to the demands of the I
2
C bus protocol function, the SDA pin must be connected to a pull-up resistor
(with a resistance from several k to several tens of k) without fail. The appropriate value must be
selected for this resistance (R
PU
) on the basis of the V
IL
and I
IL
of the microcontroller and other devices
controlling this product as well as the V
OL
– I
OL
characteristics of the product. Generally, when the
resistance is too high, the operating frequency will be restricted; conversely, when it is too low, the
operating current consumption will increase.
R
PU
maximum value
The maximum resistance must be set in such a
way that the bus potential, which is determined
by the sum total (I
L
) of the input leaks of the
devices connected to the SDA bus and by R
PU
,
can completely satisfy the input high level (V
IH
min) of the microcontroller and EEPROM.
However, a resistance value that satisfies SDA
rise time tR and fall time tF must be set.
R
PU
maximum value = (V
DD
V
IH
) / I
L
Example: When V
DD
= 3.0 V and I
L
= 2 A
R
PU
maximum value = (3.0 V 3.0 V 0.8) / 2 A = 300 k
R
PU
minimum value
A resistance corresponding to the low-level output voltage (V
OL
max) of EEPROM must be set.
R
PU
minimum value = (V
DD
V
OL
) / I
OL
Example: When V
DD
= 3.0 V, V
OL
= 0.4 V and I
OL
= 1 mA
R
PU
minimum value = (3.0 V 0.4) / 1 mA = 2.6 k
Recommended R
PU
setting
R
PU
is set to strike a good balance between the operating frequency requirements and power
consumption. If it is assumed that the SDA load capacitance is 50 pF and the SDA output data strobe
time is 500 ns, R
PU
will be about R
PU
= 500 ns/50 pF = 10 k.
Start
Condition
Start
Condition
SCL
SDA
1
2
8
9
Dummy clock x 9
Master
Device
EEPROM
SDA
C
BUS
R
PU
I
I
L
