M48T201Y datasheet(26/37 Pages) STMICROELECTRONICS

26 / 37 page

Clock operation

M48T201Y, M48T201V

26/37

3.13

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 0.1 µF (as shown in

Figure 12) 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, STMicroelectronics recommends

connecting 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 12.

Supply voltage protection

AI00605

VCC

0.1

μF

DEVICE

VCC

VSS

M48T201Y データシート(PDF) 26 Page - STMicroelectronics