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LE24LB642CS Datasheet(PDF) 9 Page - Sanyo Semicon Device |
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LE24LB642CS Datasheet(HTML) 9 Page - Sanyo Semicon Device |
9 / 11 page LE24LB642CS 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. Start condition SCL SDA 1 2 8 9 Dummy clock cycle × 9 Start condition 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 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 Master device EEPROM SDA CBUS RPU IL IL Example: When VDD=2.5V and IL= 2μA RPU maximum value = (2.5V − 2.5V × 0.8)/2μA = 250kΩ 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=2.5V, VOL = 0.4V and IOL = 1mA RPU minimum value = (2.5V − 0.4)/1mA = 2.1kΩ 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. No.A1464-9/11 |
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