LM3S1918 Luminary Micro, Inc, LM3S1918 Datasheet - Page 123

• Manufacturer Part Number: LM3S1918
• Description: Lm3s1918 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

7.2.3
July 26, 2008
Figure 7-3. Clock Source Using Dedicated Oscillator
Note:
Battery Management
The Hibernation module can be independently powered by a battery or an auxiliary power source.
The module can monitor the voltage level of the battery and detect when the voltage drops below
2.35 V. When this happens, an interrupt can be generated. The module also can be configured so
that it will not go into Hibernate mode if the battery voltage drops below this threshold. Battery
voltage is not measured while in Hibernate mode.
Important:
Note that the Hibernation module draws power from whichever source (VBAT or VDD) has the higher
voltage. Therefore, it is important to design the circuit to ensure that VDD is higher that VBAT under
nominal conditions or else the Hibernation module draws power from the battery even when VDD
is available.
The Hibernation module can be configured to detect a low battery condition by setting the LOWBATEN
bit of the HIBCTL register. In this configuration, the LOWBAT bit of the HIBRIS register will be set
when the battery level is low. If the VABORT bit is also set, then the module is prevented from entering
Hibernation mode when a low battery is detected. The module can also be configured to generate
an interrupt for the low-battery condition (see “Interrupts and Status” on page 125).
Voltage
X
R
C
R
See “Hibernation Module” on page 458 for specific parameter values.
1
L
1,2
PU
Input
= Crystal frequency is f
= Load resistor is R
System level factors may affect the accuracy of the low battery detect circuit. The
designer should consider battery type, discharge characteristics, and a test load during
battery voltage measurements.
= Capacitor value derived from crystal vendor load capacitance specifications.
= Pull-up resistor (1 M½).
R
Regulator
or Switch
IN
PU
EN
OUT
external wake
Open drain
up circuit
XOSC_LOAD
(f
XOSC_XTAL
Source
EXT_OSC
Clock
Preliminary
.
)
.
N.C.
R
Term
Stellaris Microcontroller
VDD
XOSC0
XOSC1
HIB
WAKE
GND
VBAT
LM3S1918 Microcontroller
3 V
Battery
123