M48T559Y datasheet(13/18 Pages) STMICROELECTRONICS

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M48T559Y

BATTERY LOW WARNING

The M48T559Y checks its battery voltage on pow-

er-up. The BL (Battery Low) bit (D4 of 1FF0h) will

be set on power-up if the battery voltage is less

than 2.5V (typical).

POWER-ON DEFAULTS

Upon application of power to the device, the fol-

lowing register bits are set to a ’0’ state: WDS;

BMB0-BMB4; RB0-RB1; AFE; ABE; W; R; FT.

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 ceramic by-

pass capacitor value of 0.1µF (as shown in Figure

14) 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-

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.

Table 12. Reset AC Characteristics (TA = 0 to 70°C; VCC = 4.5V to 5.5V)

Symbol

Parameter

Min

Max

Unit

tR1

RSTIN1 Low to RST Low

200

tR2

RSTIN2 Low to RST Low

100

tR1HRZ

RSTIN1 High to RST Hi-Z

200

tR2HRZ

RSTIN2 High to RST Hi-Z

200

Figure 12. Reset Timing Waveforms

AI01679

RSTIN1

RST

RSTIN2

tR1

tR1HRZ

Hi-Z

tR2

tR2HRZ

Hi-Z

Figure 13. Supply Voltage Protection

AI02169

VCC

0.1

µF

DEVICE

VCC

VSS

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