BU9891GUL-W Datasheet, PDF (15/18 Pages) Rohm – WL-CSP EEPROM family Microwire Bus

BU9891GUL-W
Technical Note
7) Notes on power ON/OFF
・At power ON/OFF, set CS “L”.
When CS is “H”, this IC gets in input accept status (active). If power is turned on in this status, noises and the likes may
cause malfunction, mistake write or so. To prevent these, at power ON, set CS “L”. (When CS is in “L” status, all inputs
are cancelled.) And at power decline, owing to power line capacity and so forth, low power status may continue long. At
this case too, owing to the same reason, malfunction, mistake write may occur, therefore, at power OFF too, set CS “L”.
VCC
VCC
GND
VCC
CS
GND
Bad example
Good example
Fig.55 Timing at power ON/OFF
(Bad example)CS pin is pulled up to Vcc.
In this case, CS becomes “H” (active status), and EEPROM may have malfunction,
mistake write owing to noise and the likes.
Even when CS input is High-Z, the status becomes like this case, which please note.
(Good example)It is “L” at power ON/OFF.
Set 10ms or higher to recharge at power OFF.
When power is turned on without observing this condition,
IC internal circuit may not be reset, which please note.
○POR citcuit
This IC has a POR (Power On Reset) circuit as a mistake write countermeasure. After POR action, it gets in write
disable status. The POR circuit is valid only when power is ON, and does not work when power is OFF. However, if CS
is “H” at power ON/OFF, it may become write enable status owing to noises and the likes. For secure actions, observe
the follwing conditions.
1. Set CS=”L”
2. Turn on power so as to satisfy the recommended conditions of tR, tOFF, Vbot for POR circuit action.
tR
VCC
Recommended conditions of tR, tOFF, Vbot
t_R
t_OFF
Vbot
tOFF
Vbot
10m s or below 10m s or higher 0.3V or below
100m s or below 10m s or higher 0.2V or below
0
○LVCC circuit
Fig.56 Rise waveform diagram
LVCC (VCC-Lockout) circuit prevents data rewrite action at low power, and prevents wrong write.
At LVCC voltage (Typ.=1.2V) or below, it prevent data rewrite.
8) Noise countermeasures
○VCC noise (bypass capacitor)
When noise or surge gets in the power source line, malfunction may occur, therefore, for removing these, it is
recommended to attach a by pass capacitor (0.1μF) between IC VCC and GND, At that moment, attach it as close to IC
as possible.And, it is also recommended to attach a bypass capacitor between board VCC and GND.
○SK noise
When the rise time (tR) of SK is long, and a certain degree or more of noise exists, malfunction may occur owing to clock
bit displacement. To avoid this, a Schmitt trigger circuit is built in SK input. The hysteresis width of this circuit is set about
0.2V, if noises exist at SK input, set the noise amplitude 0.2Vp-p or below. And it is recommended to set the rise time
(tR) of SK 100ns or below. In the case when the rise time is 100ns or higher, take sufficient noise countermeasures.
Make the clock rise, fall time as small as possible.
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15/17
2010.07 - Rev.A