M48T08 datasheet(17/30 Pages) STMICROELECTRONICS

17 / 30 page

M48T08, M48T08Y, M48T18

Clock operations

17/30

Figure 8.

Crystal accuracy across temperature

Figure 9.

Clock calibration

VCC noise and negative going transients

ICC transients, including those produced by output switching, can produce voltage

fluctuations, resulting in spikes on the VCC bus. These transients can be reduced if

capacitors are used to store energy 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 ceramic bypass capacitor value of 0.1µF (as shown in

Figure 10) is recommended in order to provide the needed filtering.

In addition to transients that are caused by normal SRAM operation, power cycling can

generate negative 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 connect a

schottky diode from VCC to VSS (cathode connected to VCC, anode to VSS). Schottky diode

AI02124

-80

-60

-100

-40

-20

ΔF

= -0.038

(T - T

2 ± 10%

ppm

0 = 25 °C

ppm

°C

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION

M48T08 Datasheet(PDF) 17 Page - STMicroelectronics