LE2464C datasheet(13/16 Pages) ONSEMI

13 / 16 page

LE2464C

www.onsemi.com

Master

Device

EEPROM

SDA

CBUS

RPU

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

2C 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 (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 value

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 = (VCC  VIH) / IL

Example : When VCC = 3.0 V and IL = 2 A

RPU maximum value = (3.0 V  3.0 V  0.8) / 2 A = 300 k

RPU minimum value

A resistance corresponding to the low-level output voltage (VOL max) of EEPROM must be set.

RPU minimum value = (VCC  VOL) / IOL

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

RPU minimum value = (3.0 V  0.4) / 1 mA = 2.6 k

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 50 pF and the SDA output data strobe

time is 500 ns, RPU will be about RPU = 500 ns/50 pF = 10 k.

Start

Condition

Start

Condition

SCL

SDA

Dummy clock x 9

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