LE24LB642M

No.1201-10/12

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

resistance from several k

Ω to several tens of kΩ) without fail. The appropriate value must be selected for this

resistance (RPU) on the basis of the VIL and IIL of the microcontroller and other devices controlling this product as

well as the VOL–IOL 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.

RPU maximum resistance

The maximum resistance must be set in such a way that the bus potential, which is determined by the sum total (IL)

of the input leaks of the devices connected to the SDA bus and by RPU, can completely satisfy the input high level

(VIH min) of the microcontroller and EEPROM. However, a resistance value that satisfies SDA rise time tR and fall

time tF must be set.

RPU maximum value = (VDD - VIH)/IL

Example: When VDD=3.0V and IL= 2μA

RPU maximum value = (3.0V − 3.0V × 0.8)/2μA = 300kΩ

RPU minimum value

A resistance corresponding to the low-level output

voltage (VOL max) of SANYO’s EEPROM must be set.

RPU minimum value = (VDD − VOL)/IOL

Example: When VDD=3.0V, VOL = 0.4V and IOL = 1mA

RPU minimum value = (3.0V − 0.4)/1mA = 2.6kΩ

Recommended RPU setting

RPU 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 50pF and the SDA output data strobe time is 500ns, RPU will be about

RPU = 500ns/50pF = 10kΩ.

Master

device

EEPROM

SDA

CBUS

RPU

IL

IL

Start condition

Dummy clock cycle

× 9

Start condition

SCL

SDA

1

2

8

9