HT1382_1105 HOLTEK [Holtek Semiconductor Inc], HT1382_1105 Datasheet - Page 9

• Manufacturer Part Number: HT1382_1105
• Description: I2C/3-Wire Real Time Clock
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

HT1382
I
Functional Description
Rev. 1.40
2
C/3-Wire Real Time Clock
Power Control Function
V
Normal Mode (V
Battery Backup Mode (V
Low Power Mode
V
COMP
V
BAT
DD
Note: Battery switchover when V
V
The HT1382 is a low power real time clock device which provides full date and time functions.
Communication with the device is provided through two integral serial interfaces, I
device version selects the type of interface. The clock and calendar information is generated in BCD
format and also has alarm features. The calendar is accurate until the year 2099, with automatic leap
year correction.
Basic timing is provided using an external 32768Hz crystal, for which the device includes load
capacitances of 12.5pF. An oscillator compensation function is provided to compensate for crystal
oscillator temperatures. With fully integrated power control circuitry which can detect power failures,
the device can automatically switch to a reserve battery supply when a power failure occurs.
The internal battery switchover circuit continually monitors the main power supply on the VDD pin
and automatically switches to the backup battery supply when a power failure condition is detected.
In the battery backup mode, the interface is disabled to minimise power consumption. The interface
inputs will not be recognized which prevents extraneous data being written to the device. The interface
outputs are high-impedance. All RTC function are operational when the device is in the battery backup
mode.
To switch from the V
V
To switch from the V
V
The power control situation is illustrated graphically below:
In normal mode, the HT1382 switched into battery backup mode when the V
ensure that the device can accept a wide range of backup voltages from many types of sources while
reliably switching into backup mode. Another mode, called Low Power Mode, is available to allow
direct switching from V
circuit is disabled and less power is used while operating from V
the LPM bit.
Low Power Mode is useful when V
V
switchover. In a system with V
recommended to use Low Power Mode in V
BAT
DD
DD
BAT
-V
< V
> V
when V
BATHYS
BAT
BAT
-V
+ V
DD
DD
Backup
BATHYS
Battery
) to Battery Backup Mode (V
Mode
drops below V
BATHYS
and V
or V
BAT
DD
BAT
) to Normal Mode (V
DD
to V
V
DD
to V
DD
BAT
< V
> V
BAT
to V
+V
BAT
DD
BAT
COMP
< V
COMP
BATHYS
Mode , both of the following conditions must be valid:
Mode, one of the following conditions must be valid:
DD
BAT
, with about 40mVof hysteresis to prevent any switchback of V
2.55V
2.0V
=5V and V
COMP
+ V
without requiring V
DD
is normally higher than V
COMPHYS
9
BAT
BAT
DD
DD
V
=3V, Low Power Mode can be used. However, it is not
=3.3V 10%, V
)
)
V
COMP
V
BAT
DD
Note: Battery switchover when V
V
COMP
DD
to drop below V
Battery Backup
BAT
BAT
DD
. The device will switch from V
3V.
Mode
. Low Power Mode is activated via
COMP
DD
. The power switchover
V
power is lost. This will
COMP
BAT
+V
> V
2
C or 3-wire. The
3.0V
2.55V
COMPHYS
COMP
May 27, 2011
DD
after
DD
to