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BU9883FV-W
Datasheet
● Cautions on microcontroller connection
Rs
In I2C 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. The following SCL SDA R PU and R S correspond to them of each
port.
ACK
SCL
R PU
R S
SDA
'H' output of microcontroller
'L' output of EEPROM
Microcontroller
EEPROM
Over current flows to SDA line by 'H'
output of microcontroller and 'L'
output of EEPROM.
Figure 51. I/O circuit diagram
Figure 52. Input / output collision timing
○ Maximum value of Rs
The maximum value of Rs is determined by the following relations. The following V CC , V OL , R S , R PU , I OL , and SDA
correspond to them of each port.
(1)SDA rise time to be determined by the capacity (CBUS) of bus line of Rpu and SDA should be tR or below.
And AC timing should be satisfied even when SDA rise time is late.
A
(2)The bus electric potential to be determined by Rpu and Rs the moment when EEPROM outputs 'L' to SDA bus should
sufficiently secure the input 'L' level (V IL ) of microcontroller including recommended noise margin 0.1V CC .
V CC
R PU
A
(V CC － V OL )×R S
R PU +R S
+
V OL +0.1V CC ≦ V IL
R S
V OL
I OL
Bus line
∴
R S
≦
V IL － V OL － 0.1V CC
1.1V CC － V IL
×
R PU
capacity CBUS
Example ） When V CC =3V, 　 V IL =0.3V CC, 　 V OL =0.4V, 　 R PU =20k ? ,
V IL
Microcontroller EEPROM
Figure 53. I/O circuit diagram
from(2),
R S
≦
0.3×3 － 0.4 － 0.1×3
1.1×3 － 0.3×3
×
20×10 3
○ Minimum value of Rs
≦ 1.67 ［ k ? ］
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. The following V CC , R PU , R S , and I correspond to
them of each port.
R PU
R S
'L' output
V CC
R S
∴ R S
≦
≧
I
V CC
I
Over current Ⅰ
'H' output
Example ） When V CC =3V, I=10mA
Microcontroller
EEPROM
R S
≧
3
10×10 -3
Figure 54. I/O circuit diagram
≧ 300 ［Ω］
www.rohm.com
? 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111 ? 15 ? 001
21/25
TSZ02201-0R2R0G100420-1-2
31.AUG.2012 Rev.001
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