Datasheet

Technical Note
12/18
BR25S□□□ Series
www.rohm.com
2010.12 - Rev.B
© 2010 ROHM Co., Ltd. All rights reserved.
●I/O peripheral circuits
In order to realize stable high speed operations, pay attention to the following input / output pin conditions.
○Input pin pull up, pull down resistance
When to attach pull up, pull down resistance to EEPROM input pin, select an appropriate value for the microcontroller
VOL, IOL with considering VIL characteristics of this IC.
1. Pull up resistance
And, in order to prevent malfunction or erroneous write at power ON/OFF, be sure to make CSB pull up.
2.Pull down resistance
Further, by amplitude VIHE, VILE of signal input to EEPROM, operation speed changes. By inputting Vcc/GND level
amplitude of signal, more stable high speed operations can be realized. On the contrary, when amplitude of 0.8VCC /
0.2Vcc is input, operation speed becomes slow.
*1
In order to realize more stable high speed operation, it is recommended to make the values of R
PU
, R
PD
as large as
possible, and make the amplitude of signal input to EEPROM close to the amplitude of VCC / GND level.
(
*
1 In this case, guaranteed value of operating timing is guaranteed.)
○SO load capacity condition
Load capacity of SO output pin affects upon delay characteristic of SO output (Data output delay time, time from HOLDB
to High-Z, Output rise time, Output fall time.). In order to make output delay characteristic into better, make SO load
capacity small.
○Other cautions
Make the each wire length from the microcontroller to EEPROM input pin same length, in order to prevent setup / hold
violation to EEPROM, owing to difference of wire length of each input.
EEPROM
SO
C
L
Fig.47 SO load capacity
Fig.45 Pull up resistance
Fig.46 Pull down resistance
R
PD
≧
V
OHM
I
OHM
･･･③
V
OHM
≧ V
IHE
･･･④
Example) When V
CC
=5V, V
OHM
=V
CC
-0.5V, I
OHM
＝0.4mA,
V
IHE
=V
CC
×0.7V, from the equation③,
R
PD
≧
5－0.5
0.4×10
-
3
∴R
PD
≧ 11.3[kΩ]
R
PU
≧
V
CC
－V
OLM
I
OLM
･･･①
V
OLM
≦ V
ILE
･･･②
R
PU
≧
5－0.4
2×10
-
3
∴R
PU
≧ 2.3[kΩ]
With the value of Rpu to satisfy the above equation, V
OLM
becomes 0.4V or lower, and with V
ILE
(=1.5V), the equation ② is
also satisfied.
・V
ILE
:EEPROM V
IL
specifications
・V
OLM
:Microcontroller V
OL
specifications
・I
OLM
:Microcontroller I
OL
specifications
Example) When Vcc=5V, V
ILE
=1.5V, V
OLM
=0.4V, I
OLM
=2mA,
from the equation ①,
I
OLM
V
ILE
V
OLM
“L” output “L” input
Microcontroller
EEPROM
R
PU
I
OHM
V
IHE
V
OHM
Microcontroller
EEPROM
“H” output “H” input
R
PD