BR24C21_11 Datasheet, PDF (19/23 Pages) Rohm – EDID Memory (For display)

BR24C21,BR24C21F,BR24C21FJ,BR24C21FV,
BU9882-W,BU9882F-W,BU9882FV-W
Technical Note
●Notes For Power Supply
VCC rises through the low voltage region in which the internal circuit of the IC and the controller are unstable. Therefore,
the device may not work properly due to an incomplete reset of the internal circuit. To prevent this, the device has a P.O.R.
and LVCC feature. At power up, maintain the following conditions to ensure functions of P.O.R and LVCC.
1. "SDA='H'" and "SCL='L' or 'H'".
2. Follow the recommended conditions of tR, tOFF, Vbot for the P.O.R. function during power up.
tR
VCC
Recommended conditions of tR, tOFF, Vbot
tR
tOFF
Vbot
tOFF
Vbot
0
Fig.33 Vcc rising wave from
Below 10ms
Below 100ms
Above 10ms
Above 10ms
Below 0.3V
Below 0.2V
3. Prevent SDA and SCL from being "Hi-Z".
In case conditions 1 and/or 2 cannot be met, take following actions:
A)If unable to keep condition 1 ( SDA is "Low" during power up):
→Control SDA ,SCL to be "High" as shown in figure below.
VCC
SCL
tLOW
SDA
After Vcc becoms stable
After Vcc becoms stable
tDH tSU:DAT
tSU:DAT
Fig.34 SCL="H" and SDA="L"
Fig.35 SCL="L" and SDA="L"
B)If unable to keep condition 2.
→After power becomes stable, execute software reset. (See Fig.29)
C)If unable to keep both conditions 1 and 2.
→Follow the instruction A first, then the instruction B.
●LVCC Circuit
LVCC circuit inhibits write operation at low voltage, and prevents an inadvertent write. Write operation is inhibited below the
LVCC voltage (Typ.=1.2V).
●Vcc NOISE
○Bypass Condenser
Noise and surges on power line may cause abnormal function. It is recommended that the bypass condensers (0.1µF) are
attached on the Vcc and GND line beside the device. It is also recommended to attach bypass condensers on the board
close to the connector.
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19/22
2011.08 - Rev.C