Linear Technology DC1812A Demo Manual page 7

Quikeval interface
To avoid unnecessary calculation, the interface conveniently
suggests a prescalar value to use based on the entered
battery capacity and sense resistor value. This prescalar
can be overridden by the user with the help of the prescalar
dropdown box. In the case of an override, the prescalar
dropdown box will be colored red giving a visual cue that
the prescalar chosen is not the suggested one.
The interface also warns the user in case the current is
too small with respect to the battery capacity by giving
an error message similar to the one shown in Figure 6.
Figure 6. Low Current Warning
Initializing the Accumulated Charge Register
By default, the ACR register has the initial value of 0x7FFF.
The ACR register can be initialized to full, empty or set to
a user defined level based on battery capacity.
The "From Voltage (Li-ion Only)" button gives an estimate
of the initial ACR value by sensing the voltage and ambient
temperature of the battery being used. It compares the
voltage and temperature values to the discharge curves of
a Panasonic CGR18650CG lithium ion battery to estimate
the battery's state of charge. Due to the fact that the dis-
charge curve for each lithium ion battery is different, the
state of charge calculated this way might not be accurate.
It is strongly advised to use a characterized battery whose
state of charge is already known and to initialize the ACR
value accordingly.
DEMO MANUAL DC1812A
Battery Gas Gauge
The gas gauge shows the battery's state of charge. The
upper battery limit is always 0xFFFF while the lower limit
is dependent on the battery capacity and q
lower limit is calculated based off of R
M, and displayed in hexadecimal in the lower right corner
of the gas gauge. Battery charge percentage as well as the
ACR register value is shown alongside the gas gauge. The
amount of charge left is also represented in mAh under
the battery widget.
Figure 7. Battery Gas Gauge
size. This
LSB
and prescalar
SENSE
dc1812af
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