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BR24L01AFV-WE2 데이터시트(PDF) 35 Page - Rohm |
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BR24L01AFV-WE2 데이터시트(HTML) 35 Page - Rohm |
35 / 41 page Technical Note 35/40 www.rohm.com 2009.09 - Rev.D © 2009 ROHM Co., Ltd. All rights reserved. BR24L□□-W Series,BR24S□□□-W Series ●Cautions on microcontroller connection ○Rs In I 2C BUS, it is recommended that SDA port is of open drain input/output. However, when to use CMOS input / output of tri state to SDA port, insert a series resistance Rs between the pull up resistance Rpu and the SDA terminal of EEPROM. This is controls over current that occurs when PMOS of the microcontroller and NMOS of EEPROM are turned ON simultaneously. Rs also plays the role of protection of SDA terminal against surge. Therefore, even when SDA port is open drain input/output, Rs can be used. ○Maximum value of Rs The maximum value of Rs is determined by following relations. (1)SDA rise time to be determined by the capacity (CBUS) of bus line of Rpu and SDA shoulder be tR or below. And AC timing should be satisfied even when SDA rise time is late. (2)The bus electric potential ○ A to be determined by Rpu and Rs the moment when EEPROM outputs 'L' to SDA bus should sufficiently secure the input 'L' level (VIL) of microcontroller including recommended noise margin 0.1Vcc. ○Maximum value of Rs The minimum value of Rs is determined by over current at bus collision. When over current flows, noises in power source line, and instantaneous power failure of power source may occur. When allowable over current is defined as I, the following relation must be satisfied. Determine the allowable current in consideration of impedance of power source line in set and so forth. Set the over current to EEPROM 10mA or below. (VCC-VOL)×RS + VOL+0.1VCC≦VIL RPU+RS ∴ RS ≦ VIL-VOL-0.1VCC × RPU 1.1VCC-VIL Example)When VCC=3V, VIL=0.3VCC, VOL=0.4V, RPU=20k Ω from(2), RS ≦ 0.3×3-0.4-0.1×3 × 20×10 3 1.1×3-0.3×3 ≦ 1.67[k Ω] VCC ≦ I RS ∴ RS ≧ VCC I Example)When VCC=3V, I=10mA RS ≧ 3 10×10-3 RPU Microcontre RS EEPROM Fig.51 Input/output collision timing RPU Microcontroller RS EEPROM IOL A Bus line capacity CBUS VOL VCC VIL Fig.52 I/O circuit diagram Microcontroller EEPROM 'L' output RS RPU 'H' output Over currentⅠ Fig.53 I/O circuit diagram Fig.50 I/O circuit diagram ACK 'L' output of EEPROM 'H' output of microcontroller Over current flows to SDA line by 'H' output of microcontroller and 'L' output of EEPROM. SCL SDA |
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