LTC2942IDCB-1#PBF Linear Technology, LTC2942IDCB-1#PBF Datasheet - Page 11

• 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

applicaTions inFormaTion
Choosing Coulomb Counter Prescaler M B[5:3]
If the battery capacity (Q
the maximum current (I
the prescaler value M should be changed from its default
value (128).
In these applications with a small battery but a high
maximum current, q
to the battery capacity. For example, if the battery capacity
is 100mAh and the maximum current is 1A, the standard
equation leads to choosing 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 LTC2942
includes a programmable prescaler. Lowering the pres-
caler factor M allows reducing q
accumulated charge register 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
register as possible the prescaler factor M should be
chosen for a given battery capacity Q
resistor R
M can be set to 1, 2, 4, 8, … 128 by programming B[5:3] of
the control register as M = 2
value after power up is M = 128 = 2
In the above example of a 100mAh battery and an R
of 50mΩ, the prescaler should be programmed to M = 4.
The q
corresponds to roughly 37650 q
q
M≥128 •
q
LSB
LSB
LSB
= 0.085mAh = 306mC
= 0.085mAh •
then becomes 2.656µAh and the battery capacity
SENSE
2
16
as:
• 0.085mAh
Q
BAT
LSB
R
50mΩ
SENSE
MAX
can get quite large with respect
BAT
(4 • B[5] + 2 • B[4] + B[3])
) is very small compared to
) (Q
•
•
R
50mΩ
128
BAT
LSB
SENSE
LSB
M
7
s.
< I
(B[5:3] = 111).
to better match the
MAX
BAT
• 0.1 Hours)
and a sense
. The default
SENSE
LSB
s
Note that the internal digital resolution of the coulomb
counter is higher than indicated by q
charge q
is typically 299µAs for a 50mΩ sense resistor.
ADC Mode B[7:6]
The LTC2942 features an ADC which measures either
voltage on SENSE
an internal temperature sensor. The reference voltage and
clock for the ADC are generated internally.
The ADC has four different modes of operation, as shown
in Table 3. These modes are controlled by bits B[7:6] of
the control register. At power-up, bits B[7:6] are set to
[00] and the ADC is in sleep mode.
A single voltage conversion is initiated by setting the bits
B[7:6] to [10]. A single temperature conversion is started
by setting bits B[7:6] to [01]. After a single voltage or
temperature conversion, the ADC resets B[7:6] to [00]
and goes to sleep.
The LTC2942 also offers an automatic scan mode where
the ADC converts voltage, then temperature, then sleeps
for approximately two seconds before repeating the voltage
and temperature conversions. The LTC2942 is set to this
automatic mode by setting B[7:6] to [11] and stays in this
mode until B[7:6] are reprogrammed by the host.
Programming B[7:6] to [00] puts the ADC to sleep. If
control bits B[7:6] change within a conversion, the ADC
will complete the current conversion before entering the
newly selected mode.
A conversion of either voltage or temperature requires 10ms
conversion time (typical). At the end of each conversion,
the corresponding registers are updated. If the converted
quantity exceeds the values programmed in the threshold
registers, a flag is set in the status register and the AL/CC
pin is pulled low (if alert mode is enabled).
During a voltage conversion, the SENSE
through a small resistor to a sampling circuit with an
equivalent resistance of 2MΩ, leading to a mean input
current of I = V
INTERNAL
SENSE –
is M • 8 times smaller than q
–
(battery voltage) or temperature via
/2MΩ.
LSB
–
LTC2942
pin is connected
. The digitized
LSB
. q
INTERNAL

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