Functionality and Usage of the Battery Monitor
13.1 Functionality and Usage of the Battery Monitor
The battery monitor makes it possible to check whether the supply voltage (
AVDD5
) is above or below a
certain programmable level. Its usage is controlled by the
BATTMON
register in the following manner:
BATTMON_VOLTAGE
is used to set the trigger point for the battery monitor. Note the fact that the step size
is different for different voltage ranges (see the register description in
for details). This is
done to achieve good accuracy in the voltage areas around 2 V, with lower resolution at higher voltages.
BATTMON_PD
is used to enable/disable the battery monitor.
After enabling the battery monitor by setting
BATTMON_PD = 0
and waiting for at least 2
µ
s, the value of
BATTMON_OUT
indicates whether the voltage is above or below the trigger point (set by
BATTMON_VOLTAGE
).
NOTE:
One should turn the battery monitor off (
BATTMON_PD
= 1) after reading the measurement
BATTMON_OUT
in order to save power, as the battery monitor consumes power when
enabled ( = 0).
Recommended usage of the battery monitor can be summarized in the following way:
1. Set
BATTMON_VOLTAGE
to the value to be monitored.
2. Enable the battery monitor by setting
BATTMON_PD = 0
.
3. Wait for at least 2
µ
s.
4. Read the
BATTMON_OUT
result to see whether the voltage level is above or below the value set in
BATTMON_VOLTAGE
.
5. Disable the battery monitor (
BATTMON_PD = 1
) to avoid unnecessary current consumption.
13.2 Using the Battery Monitor for Temperature Monitoring
The battery monitor can also be used to do some simple temperature monitoring. When the battery
monitor is connected to the internal temperature sensor instead of the supply voltage
AVDD5
(see the
description of
MONMUX
in
), it can indicate whether the temperature is above or below a
certain level. This is done by comparing the voltage coming from the temperature sensor to the voltage
trigger point of the battery monitor. The controls for this measurement are the same as for the normal use
of the battery monitor (see the description of
BATTMON
in
It is important to understand that due to the nature of the battery monitor (optimized for voltages arround 2
V) and the output voltage range of the temperature sensor, there are only about 8 temperature trigger
values in the temperature range of
–
40
°
C to 125
°
C (see
). As a result, the battery monitor gives
only a rough indication of the temperature range, but this is useful for doing temperature compensation on
analog components in a system. See the device's data sheet (
) for performance characteristics
details.
Table 13-1. Values Showing How Different
Temperatures Relate to
BATTMON_VOLTAGE
for a
Typical Device
Temperature
BATTMON_VOLTAGE
-40
°
C
22
-26
°
C
21
-11
°
C
20
7
°
C
19
25
°
C
18
47
°
C
17
70
°
C
16
97
°
C
15
128
°
C
14
146
Battery Monitor
SWRU191C
–
April 2009
–
Revised January 2012
Copyright
©
2009
–
2012, Texas Instruments Incorporated