BU9888FV-W Datasheet, PDF (13/17 Pages) Rohm – High Reliability Serial EEPROMs

BU9888FV-W
Technical Note
○Selection of resistance value R
The resistance R becomes through current limit resistance at data collision. When through current flows, noises of power
source line and instantaneous stop of power source may occur. When allowable through current is defined as I, the
following relation should be satisfied. Determine allowable current amount in consideration of impedance and so forth of
power source line in set. And insert resistance R, and set the value R to satisfy EEPROM input level VIH/VIL even under
influence of voltage decline owing to leak current and so forth. Insertion of R will not cause any influence upon basic
operations.
(1) Address data A0 = “1” input, dummy bit “0” output timing
(When microcontroller DI/O output is “H”, EEPROM DO outputs “L”, and “H” is input to DI)
・Make the through current to EEPROM 10mA or below.
・See to it that the level VIH of EEPROM should satisfy the following.
Microcontroller
EEPROM
DI/O PORT
DI
“H” output
VOHM
IOHM
R
DO
VOLE
“L” output
Conditions
VOHM ≦ VIHE
VOHM ≦ IOHM×R + VOLE
At this moment, if VOLE=0V,
VOHM ≦ IOHM×R
∴
R≧
VOHM
IOHM
・・・⑦
・VIHE : EEPROM VIH specifications
・VOLE : EEPROM VOL specifications
・VOHM : Microcontroller VOH specifications
・IOHM : Microcontroller IOH specifications
Fig.46 Circuit at DI, DO direct connection (Microcontroller DI/O “H” output, EEPROM “L” output)
(2) DO status READY output timing
(When the microcontroller DI/O is “L”, EEPROM DO output “H”, and “L” is input to DI)
・Set the EEPROM input level VIL so as to satisfy the following.
Conditions
Microcontroller
“L” output ^{DI/O PORT}
VOLM
EEPROM
DI
IOHM
R
DO
VOHE
“H” output
VOLM ≧ VILE
VOLM ≧ VOHE – IOLM×R
As this moment, VOHE=Vcc
VOLM ≧ Vcc – IOLM×R
Vcc – VOLM
∴
IOLM
・・・⑧
・VILE
・VOHE
・VOLM
・IOLM
: EEPROM VIL specifications
: EEPROM VOH specifications
: Microcontroller VOL specifications
: Microcontroller IOL specifications
Fig.47 Circuit at DI, DO direct connection (Microcontroller DI/O “L” output, EEPROM “H” output)
Example) When Vcc=5V, VOHM=5V, IOHM=0.4mA, VOLM=5V, IOLM=0.4mA,
From the equation ⑦,
From the equation⑧,
R ≧ ^VOHM
IOHM
R≧
5
0.4×10^-3
R ≧ ^{Vcc – VOLM}
IOLM
R ≧ ^{5 – 0.4}
2.1×10^-3
∴
R ≧ 12.5 [kΩ] ・・・⑨
∴
R ≧ 2.2 [kΩ] ・・・⑩
Therefore, from the equations ⑨ and ⑩,
∴
R ≧ 12.5 [kΩ]
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13/16
2011.01 - Rev.A