M48Z35AY, M48Z35AV

10/16

If the voltage is less than approximately 2.5V, an

internal Battery Not OK (BOK) flag will be set. The

BOK flag can be checked after power up. If the

BOK flag is set, the first write attempted will be

blocked. The flag is automatically cleared after the

first write, and normal RAM operation resumes.

Figure 9 illustrates how a BOK check routine could

be structured.

For more information on Battery Storage Life refer

to the Application Note AN1012.

Figure 10. Supply Voltage Protection

AI02169

VCC

0.1

µF

DEVICE

VCC

VSS

Figure 9. Checking the BOK Flag Status

READ DATA

AT ANY ADDRESS

AI00607

IS DATA

COMPLEMENT

OF FIRST

READ?

(BATTERY OK)

POWER-UP

YES

NO

WRITE DATA

COMPLEMENT BACK

TO SAME ADDRESS

READ DATA

AT SAME

ADDRESS AGAIN

NOTIFY SYSTEM

OF LOW BATTERY

(DATA MAY BE

CORRUPTED)

WRITE ORIGINAL

DATA BACK TO

SAME ADDRESS

(BATTERY LOW)

CONTINUE

POWER SUPPLY DECOUPLING and

UNDERSHOOT PROTECTION

switching, can produce voltage fluctuations, re-

can be reduced if capacitors are used to store en-

stored in the bypass capacitors will be released as

low going spikes are generated or energy will be

absorbed when overshoots occur. A ceramic by-

pass capacitor value of 0.1µF (as shown in Figure

10) is recommended in order to provide the need-

ed filtering.

In addition to transients that are caused by normal

SRAM operation, power cycling can generate neg-

tive spikes can cause data corruption in the SRAM

while in battery backup mode. To protect from

these voltage spikes, it is recommended to con-

1N5817 is recommended for through hole and

MBRS120T3 is recommended for surface mount.