IDT1338
REAL-TIME CLOCK WITH BATTERY BACKED NON-VOLATILE RAM
RTC
Power Control
A precise, temperature-compensated voltage reference and
a comparator circuit provides power-control function that
monitors the
V
CC
level. The device is fully accessible and
data can be written and read when
V
CC
is greater than V
PF
.
However, when
V
CC
falls below V
PF
, the internal clock
registers are blocked from any access. If V
PF
is less than
V
BAT
, the device power is switched from
V
CC
to V
BAT
when
V
CC
drops below V
PF
. If V
PF
is greater than V
BAT
, the device
power is switched from
V
CC
to V
BAT
when
V
CC
drops below
V
BAT
. The registers are maintained from the V
BAT
source
until
V
CC
is returned to nominal levels (Table 1). After
V
CC
returns above V
PF
, read and write access is allowed after
t
REC
(see the “Power-Up/Down Timing” diagram).
Table 1. Power Control
Supply Condition
V
CC
< V
PF
, V
CC
<
V
BAT
V
CC
< V
PF
, V
CC
>
V
BAT
V
CC
> V
PF
, V
CC
<
V
BAT
V
CC
> V
PF
, V
CC
>
V
BAT
Read/Write
Access
No
No
Yes
Yes
Powered
By
V
BAT
V
CC
V
CC
V
CC
Power-up/down Timing
Table 2. Power-up/down Characteristics
Ambient Temperature -40 to +85° C
Parameter
Recovery at Power-up
V
CC
Fall Time; V
PF(MAX)
to V
PF(MIN)
V
CC
Rise Time; V
PF(MIN)
to V
PF(MAX)
Symbol
t
REC
t
VCCF
t
VCCR
Conditions
(see note below)
Min.
300
0
Typ.
Max.
2
Units
ms
µs
µs
Note:
This delay applies only if the oscillator is running. If the oscillator is disabled or stopped, no power-up delay
occurs.
IDT™
REAL-TIME CLOCK WITH BATTERY BACKED NON-VOLATILE RAM 5
IDT1338
REV J 111009
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
