M48T35 datasheet(12/18 Pages) STMICROELECTRONICS

12 / 18 page

M48T35, M48T35Y

12/18

POWER SUPPLY DECOUPLING and

UNDERSHOOT PROTECTION

ICC transients, including those produced by output

switching, can produce voltage fluctuations, re-

sulting in spikes on the 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 11) 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 nega-

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-

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 10. Crystal Accuracy Across Temperature

AI00999

–160

10203040506070

Frequency (ppm)

Temperature

°C

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

–20

∆F

= -0.038

(T - T

± 10%

ppm

0 = 25 °C

Figure 11. Supply Voltage Protection

AI02169

VCC

0.1

µF

DEVICE

VCC

VSS

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