Datasheet

LP3972
www.ti.com SNVS468K –SEPTEMBER 2006–REVISED MAY 2013
Controls Port Function Reg batmonchg
GPIO<1> GPIO<1> Nextchgen_sel bucen GPIO1 Gpin 1 Function
1 1 0 X Output = 1 0
GPIO<1> GPIO<1> Factory fm disabled GPIO_tstiob GPIO2 gpin2
0 0 1 HiZ 0
1 0 1 Input (dig)-> input
0 1 1 Output = 0 0
1 1 1 Output = 1 0
The LP3972 has provision for two battery connections, the main battery V
BAT
and Backup Battery (See
Applications Schematic Diagrams 1 & 2 of the LP3972 Data Sheet).
The function of the battery switch is to connect power to the LDO_RTC from the appropriate battery, depending
on conditions described below:
• If only the backup battery is applied, the switch will automatically connect the LDO_RTC power to this battery.
• If only the main battery is applied, the switch will automatically connect the LDO_RTC power to this battery.
• If both batteries are applied, and the main battery is sufficiently charged (V
BAT
> 3.1V), the switch will
automatically connect the RTC LDO power to the main battery.
• As the main battery is discharged by use, the user will be warned by a separate circuit called nBATT_FLT.
Then if no action is taken to restore the charge on the main battery, and discharging is continued the battery
switch will protect the LDO_RTC by disconnecting from the main battery and connecting to the backup
battery.
– The main battery voltage at which the LDO_RTC is switched from main to backup battery is 2.9V typically.
– There is a hysteresis voltage in this switch operation so, the LDO_RTC will not be reconnected to main
battery until main battery voltage is greater than 3.1V typically.
• Additionally, the user may wish to disable the battery switch, such as, in the case when only a main battery is
used. This is accomplished by setting the "no back up battery bit" in the control register 8h’89 bit 7 NBUB.
With this bit set to "1", the above described switching will not occur, that is the LDO_RTC will remain
connected to the main battery even as it is discharged below the 2.9 Volt threshold.
REGULATED VOLTAGES OK
All the power domains have own register bit (X_OK) that processor can read via serial interface to be sure that
enabled powers are OK (regulating). Note that these read only bits are only valid when regulators are settled
(avoid reading these bits during voltage change or power up).
THERMAL MANAGEMENT
Application: There is a mode wherein all 6 comparators (flags) can be turned on via the "enallflags" control
register bit. This mode allows the user to interrogate the device or system temperature under the set operating
conditions. Thus, the rate of temperature change can also be estimated. The system may then negotiate for
speed and power trade off, or deploy cooling maneuvers to optimize system performance. The "enallflags" bit
needs enabled only when the "bct<2:0> bits are read to conserve power.
Note: The thermal management flags have been verified functional. Presently these registers are accessible by
factory only. If there is a demand for this function, the relevant register controls may be shifted into the user
programmable bank; the temperature range and resolution of these flags, might also be refined/redefined.
THERMAL WARNING
2 of 6 low power comparators, each consumes less than 1 µA, are always enabled to operate the "T=125°C
warning flag with hysteresis. This allows continuous monitoring of a thermal-warning flag feature with very low
power consumption.
LP3972 THERMAL FLAGS FUNCTIONAL DIAGRAM, DATA FROM INITIAL SILICON
The following functions are extra features from the thermal shutdown circuit:
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