M41T81 Datasheet, PDF (14/28 Pages) STMicroelectronics – Serial Access Real-Time Clock with Alarms

M41T81
Data Retention Mode
With valid V_CC applied, the M41T81 can be ac-
cessed as described above with READ or WRITE
Cycles. Should the supply voltage decay, the pow-
er input will be switched from the V_CC pin to the
battery when V_CC falls below the Battery Back-up
Switchover Voltage (V_SO). At this time the clock
registers will be maintained by the attached bat-
tery supply. As V_CC continues to fall, the M41T81
will pass through the Register Bit Reset Voltage
(V_RST) threshold, not only write protecting itself,
but also resetting certain Control Bits (see Table
13, page 21). On power-up, when V_CC returns to a
nominal value, write protection continues for t_REC.
For a further, more detailed review of lifetime cal-
culations, please see Application Note AN1012.
Figure 17. Power Down/Up Mode AC Waveforms
VCC
VSO
tPD
SDA
SCL
DON'T CARE
tREC
AI00596
Table 8. Power Down/Up AC Characteristics
Symbol
Parameter^(1,2)
Min
Typ
t_PD
SCL and SDA at V_IH before Power Down
0
t_REC
SCL and SDA at V_IH after Power Up
10
Note: 1. V_CC fall time should not exceed 5mV/µs.
2. Valid for Ambient Operating Temperature: TA = –40 to 85°C; VCC = 2.0 to 5.5V (except where noted).
Max
Unit
nS
µS
Table 9. Power Down/Up Trip Points DC Characteristics
Sym
Parameter^(1,2)
Min
Typ
Max
V_SO Battery Back-up Switchover Voltage
V_BAT – 0.80 V_BAT – 0.50 V_BAT – 0.30
V_RST Register Bit Reset Voltage
1.1
2.0
Note: 1. All voltages referenced to V_SS.
2. Valid for Ambient Operating Temperature: T_A = –40 to 85°C; V_CC = 2.0 to 5.5V (except where noted).
Unit
V
V
14/28