Open drain
external wake
up circuit
3 V
Battery
GND
C 2
C 1
X 1
VBAT
EN
Input
Voltage
Regulator
or Switch
XOSC1
XOSC0
VDD
HIB
WAKE
OUT
IN
GNDX
7LYDŒ 0LFURFRQWUROOHU
R
BAT
C
BAT
R
PU
Functional Description
479
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Hibernation Module
Alternatively, a low frequency oscillator source (HIB LFIOSC) present in the Hibernation module can be a
clock source. (The frequency can have wide variations; see the HIB clock specifications in the device-
specific data sheet for more details.) The intent of this source is to provide an internal low-power clock
source to enable the use of the asynchronous pin wakes and memory storage without the requirement of
an external crystal. To enable the HIB LFIOSC to be the clock source for the Hibernation module, both the
OSCSEL bit and the CLK32EN bit in the Hibernation Control (HIBCTL) register must be set.
NOTE:
The HIB low-frequency oscillator (HIB LFIOSC) has a wide frequency variation, therefore the
RTC is not accurate when using this clock source. It is not recommended to use the HIB
LFIOSC as an RTC clock source.
The Hibernation module is enabled by setting the CLK32EN bit of the HIBCTL register. The CLK32EN bit
must be set before accessing any other Hibernation module register. The type of clock source used for the
HIB module is selected by setting the OSCSEL and OSCBYP bit of the HIBCTL register. If the internal low
frequency precision oscillator is used as the clock source, the OSCSEL bit should be set to a 1 at the
same time the CLK32EN bit is set. If a crystal is used for the clock source, the software must leave a
delay of t
HIBOSC_START
after writing to the CLK32EN bit and before any other accesses to the Hibernation
module registers. The delay allows the crystal to power up and stabilize. If an external oscillator is used
for the clock source, no delay is needed. When using an external clock source, the OSCBYP bit in the
HIBCTL register should be set. When using a crystal clock source, the GNDX pin should be connected to
digital ground along with the crystal load capacitors, as shown in
. When using an external clock
source, the GNDX pin should be connected to digital ground.
NOTE:
In the following figures, the parameters R
BAT
and C
BAT
have recommended values of 51
Ω
±5%
and 0.1µF ±5%, respectively. See the HIB electrical specifications in the device-specific data
sheet for more information.
Figure 6-2. Using a Crystal as the Hibernation Clock Source with a Single Battery Source