M48T58 datasheet(20/27 Pages) STMICROELECTRONICS

20 / 27 page

M48T58, M48T58Y

20/27

Figure 13. Clock Calibration

VCC Noise And Negative Going Transients

ICC transients, including those produced by output

switching, can produce voltage fluctuations, re-

sulting inspikes onthe VCC bus. These transients

can be reduced if capacitors are used to store en-

ergy which stabilizes the VCC bus. The energy

stored in the bypass capacitors will be released as

low going spikes are generated or energy will be

absorbed when overshoots occur. A bypass ca-

pacitor value of 0.1µF (as shown in Figure 14) is

recommended in order to provide the needed fil-

tering.

In addition to transients that are caused by normal

SRAM operation, power cycling can generate neg-

ative voltage spikes on VCC that drive it to values

below VSS by as much as one volt. These negative

spikes can cause data corruption in the SRAM

while in battery backup mode. To protect from

these voltage spikes, it is recommended to con-

nect a schottky diode from VCC to VSS (cathode

connected to VCC, anode to VSS). Schottky diode

1N5817 is recommended for through hole and

MBRS120T3 is recommended for surface mount.

Figure 14. Supply Voltage Protection

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION

AI02169

VCC

0.1

µF

DEVICE

VCC

VSS

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