DC1496A-A Linear Technology, DC1496A-A Datasheet - Page 9

• Manufacturer Part Number: DC1496A-A
• Description: BOARD EVAL LTC2941
• Manufacturer: Linear Technology

Specifications of DC1496A-A

• Design Resources: DC1496 Design Files DC1496 Schematic
• Main Purpose: Power Management, Battery Monitor
• Embedded: No
• Utilized Ic / Part: LTC2941
• Primary Attributes: I²C, SMBus Interfaces
• Secondary Attributes: LED Status Indicators
• Kit Application Type: Power Management
• Application Sub Type: Battery Monitor
• Features: LTC2941 Device Measure Battery Charge State In Handled PC And Portable Application
• Lead Free Status / RoHS Status: Not applicable / Not applicable

applicaTions inFormaTion
The value of the external sense resistor is determined by
the maximum input range of V
current of the application:
The choice of the external sense resistor value influences
the gain of the coulomb counter. A larger sense resistor
gives a larger differential voltage between SENSE
SENSE
coulomb counting. Thus the amount of charge represented
by the least significant bit (q
(registers C, D) is given by:
when the prescaler is set to its default value of M=128.
Note that 1mAh = 3.6A • s = 3.6C (coulombs).
Choosing R
applications where:
A. the battery capacity (Q
B. the battery capacity (Q
For case A: In low current applications using a large bat-
tery, choosing R
can lead to a q
accumulated charge may underflow before the battery is
or
the maximum current (I
the maximum current (I
R
q
q
LSB
LSB
SENSE
Q
Q
–
BAT
BAT
for the same current which results in more precise
= 0.085mAh •
= 0.085mAh •
> I
< I
≤
SENSE
50
MAX
MAX
I
MAX
LSB
mV
SENSE
• 5.5 hours
• 0.1 hours
smaller than Q
= 50mV/I
R
R
according to R
50mΩ
50mΩ
SENSE
SENSE
BAT
BAT
LSB
MAX
MAX
) is very small compared to
) is very large compared to
) of the accumulated charge
MAX
):
):
•
SENSE
128
M
BAT
is not sufficient in
SENSE
/2
and the maximum
16
and the 16-bit
= 50mV/I
+
MAX
and
exhausted or overflow during charge. Choose in this case
a maximum R
In an example application where the maximum current is
I
lead to a sense resistor of 500mΩ. This gives a q
8.5µAh and the accumulated charge register can represent
a maximum battery capacity of Q
557mAh. If the battery is larger, R
For example, R
tery with a capacity of 1800mAh is used.
For case B: In applications using a small battery but having
a high maximum current, q
respect to the battery capacity. For example, if the battery
capacity is 100mAh and the maximum current is 1A, the
standard equation leads to choose a sense resistor value
of 50mΩ, resulting in:
The battery capacity then corresponds to only 1176 q
and less than 2% of the accumulated charge register is
utilized.
To preserve digital resolution in this case, the LTC2941
includes a programmable prescaler. Lowering the prescaler
factor M allows reducing q
lated charge registers C and D to the capacity of the battery.
The prescaling factor M can be chosen between 1 and its
default value 128. The charge LSB then becomes:
To use as much of the range of the accumulated charge
registers C and D as possible the prescaler factor M should
MAX
q
R
q
LSB
LSB
SENSE
= 100mA, calculating R
= 0.085mAh = 306mC
= 0.085mAh •
≤
0.085mAh • 2
SENSE
SENSE
Q
BAT
of:
must be reduced to 150mΩ if a bat-
R
50mΩ
SENSE
LSB
16
LSB
to better match the accumu-
• 50mΩ
SENSE
•
can get quite large with
128
BAT
SENSE
M
= 50mV/I
= 8.5µAh • 65535 =
LTC2941
must be lowered.
MAX
would
LSB
LSB
2941fa

of
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