LTC2942IDCB-1#PBF Linear Technology, LTC2942IDCB-1#PBF Datasheet - Page 10

• Manufacturer Part Number: LTC2942IDCB-1#PBF
• Description: IC, BATTERY FUEL GAUGE LI-ION 5.5V DFN-6
• Manufacturer: Linear Technology

Specifications of LTC2942IDCB-1#PBF

• Battery Management Function: Fuel Gauge, Charge Controller
• Battery Type: Li-Ion
• Supply Voltage Range: 2.7V To 5.5V
• Battery Ic Case Style: DFN
• No. Of Pins: 6
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC2942
applicaTions inFormaTion
Alert/Charge Complete Configuration B[2:1]
The AL/CC pin is a dual function pin configured by the
control register. By setting bits B[2:1] to [10] (default)
the AL/CC pin is configured as an alert pin following the
SMBus protocol. In this configuration the AL/CC pin is a
digital output and is pulled low if one of the three mea-
sured quantities (charge, voltage, temperature) exceeds
its high or low threshold or if the value of the accumulated
charge register overflows or underflows. An alert response
procedure started by the master resets the alert at the
AL/CC pin. For further information see the Alert Response
Protocol section.
Setting the control bits B[2:1] to [01] configures the AL/CC
pin as a digital input. In this mode, a high input on the
AL/CC pin communicates to the LTC2942 that the battery
is full and the accumulated charge register is set to its
maximum value FFFFh. The AL/CC pin would typically
be connected to the “charge complete” output from the
battery charger circuitry.
If neither the alert nor the charge complete functionality
is desired, bits B[2:1] should be set to [00]. The AL/CC
pin is then disabled and should be tied to GND.
Avoid setting B[2:1] to [11] as it enables the alert and the
charge complete modes simultaneously.
Choosing R
To achieve the specified precision of the coulomb counter,
the differential voltage between SENSE
stay within ±50mV. For differential input signals up to
±300mV the LTC2942 will remain functional but the preci-
sion of the coulomb counter is not guaranteed.
The required value of the external sense resistor, R
is determined by the maximum input range of V
the maximum current of the application:
0
R
SENSE
≤
SENSE
50
I
MAX
mV
+
and SENSE
SENSE
–
SENSE
must
and
,
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 equal to:
when the prescaler is set to its default value of M = 128.
Note that 1mAh = 3.6C (coulomb).
Choosing R
plications where the battery capacity (Q
compared to the maximum current (I
For such low current applications with a large battery,
choosing R
lead to a q
mulated charge register may underflow before the battery
is 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 capacity is larger, R
lowered. For example, R
if a battery with a capacity of 1800mAh is used.
or
MAX
Q
q
q
R
LSB
LSB
BAT
SENSE
= 100mA, calculating R
–
> I
= 0.085mAh •
= 0.085mAh •
for the same current which results in more precise
LSB
MAX
≤
SENSE
SENSE
0.085mAh • 2
smaller than Q
• 5.5 Hours
according to R
Q
= 50mV/I
SENSE
BAT
R
R
50mΩ
50mΩ
SENSE
SENSE
SENSE
of:
LSB
16
MAX
BAT
must be reduced to 150mΩ
• 50mΩ
SENSE
) of the accumulated charge
•
/2
128
SENSE
is not sufficient in ap-
BAT
M
16
= 50mV/I
and the 16-bit accu-
= 8.5µAh • 65535 =
MAX
= 50mV/I
BAT
):
SENSE
) is very large
MAX
MAX
must be
would
LSB
+
2942fa
and
can
of