BQ32002 Datasheet, PDF (20/29 Pages) Texas Instruments – BQ32002 Real-Time Clock (RTC)

BQ32002
SLUSA96B – AUGUST 2010 – REVISED APRIL 2016
www.ti.com
8.2.2 Detailed Design Procedure
8.2.2.1 Reading From a Register
The report details the read-back of the SECONDS register. Figure 9 depicts the first condition that will be used
as a benchmark to compare the values taken from the SECONDS register in the BQ32002, to the internal PC
time of the oscilloscope. In this example two modes of operation are demonstrated.
Condition 1 The main power supply, V_CC, is greater than the backup power supply, V_BACK, and the internal
reference voltage, V_REF. In this mode, the device's internal registers are fully operational with READ
and WRITE access. Analyzing Figure 9, the known register values are compared to the system
clock; in this case, the PC clock which is shown at the bottom of the screen capture.
The BQ32002 during this condition is reading back [101][0010]= [5][2], which corresponds to
52 seconds at PC time of 2:22:43 PM.
Condition 2 V_CC is now lowered to 2 V (V_BACK > V_CC). In this mode, the I²C communications are halted.
However, the internal time-keeping registers maintain full functional operation and accuracy which
will be available to be reliably read by the controller 1 second after the RTC switches from V_BACK to
V_CC supply.
Condition 3 During this final test condition, the RTC is restored to operate from the main power supply and I²C
communications are now fully functional.
Figure 10 demonstrates a read-back value from the SECONDS register of [100][0101]=
[4][5], or 45 seconds at PC time of 2:23:36 PM. This proves that the BQ32002 managed to
accurately maintain the time-keeping registers functional while the V_CC dropped below V_BACK.
8.2.2.2 Leap Year Compensation
The BQ32002 classifies a leap year as any year that is evenly divisible by 4. Using this rule allows for reliable
leap year compensation until 2100. Years that fall outside this rule will need to be compensated for by the
external controller.
8.2.2.3 Utilizing the Backup Supply
In order for the BQ32002 to achieve a low backup supply current as specified in the Electrical Characteristics,
the V_CC pin must be initialized after every total power loss situation. Initialization Is achieved by powering on V_CC
with a voltage between 3 to 3.6 V for at least 1 ms immediately after the backup supply is connected. If the V_CC
is not powered on while connecting the backup supply, then the expected leakage current from V_BACK will be
much greater than specified.
8.2.3 Application Curves
Figure 9. Master and Slave I²C Communication for the
SECONDS Register
Figure 10. Master and Slave I²C Communication for the
SECONDS Register After Recovering from the Backup
Supply
20
Submit Documentation Feedback
Product Folder Links: BQ32002
Copyright © 2010–2016, Texas Instruments Incorporated