LTC4150IMS#PBF Linear Technology, LTC4150IMS#PBF Datasheet - Page 8

• Manufacturer Part Number: LTC4150IMS#PBF
• Description: IC COUNTER/GAUGE GAS/BATT 10MSOP
• Manufacturer: Linear Technology

Specifications of LTC4150IMS#PBF

• Function: Fuel, Gas Gauge/Monitor
• Battery Type: Li-Ion, NiCd, NiMH
• Voltage - Supply: 2.7 V ~ 8.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
LTC4150
SENSE VOLTAGE INPUT AND FILTERS
Since the overall integration time is set by internally trim-
ming the LTC4150, no external timing capacitor or trimming
is necessary. The only external component that affects
the transfer function of interrupts per coulomb of charge
is the sense resistor, R
for the SENSE
maximum differential voltage range of ±50mV. SENSE
normally tied to V
when SENSE
relative to SENSE
Choose R
or discharge current, whichever is greater. Calculate
R
The sense input range is small (±50mV) to minimize the
loss across R
connections at R
The external fi lter capacitor, C
on-chip resistance of 4k to form a lowpass fi lter that
averages battery current and improves accuracy in the
presence of noise, spikes and ripple. 4.7μF is recom-
mended for general applications but can be extended to
higher values as long as the capacitor’s leakage is low.
A 10nA leakage is roughly equivalent to the input offset
error of the integrator. Ceramic capacitors are suitable
for this use.
Switching regulators are a particular concern because
they generate high levels of current ripple which may fl ow
through the battery. The V
the charger and load should be bypassed by at least 4.7μF
at the LTC4150 if a switching regulator is present.
The LTC4150 maintains high accuracy even when Burst
Mode
levels must be within the specifi ed differential input volt-
age range of 50mV as measured at C
accurate charge information, the LTC4150 must remain
enabled during Burst Mode operation. If the LTC4150
shuts down or V
charge information is lost.
8
SENSE
R
SENSE
®
from:
switching regulators are used. Burst pulse “on”
SENSE
=
–
50
I
+
SENSE
operates within the 50mV differential limit
MAX
to provide 50mV drop at maximum charge
mV
and SENSE
DD
SENSE
+
DD
.
drops below 2.5V, the part resets and
, so there is no common mode issue
. To preserve accuracy, use Kelvin
.
SENSE
DD
–
. The common mode range
pins is V
and SENSE
F
, operates against a total
F
+
DD
and C
+
±60mV, with a
connection to
F
–
. To retain
+
(1)
is
Coulomb Counting
The LTC4150’s transfer function is quantifi ed as a volt-
age to frequency gain G
number of interrupts per second and input voltage is the
differential drive V
number of interrupts per second will be:
where
Therefore,
Since I • t = Q, coulombs of battery charge per INT pulse
can be derived from Equation 4:
Battery capacity is most often expressed in ampere-
hours.
Combining Equations 5 and 6:
or
The charge measurement may be further scaled within
the microcontroller. However, the number of interrupts,
coulombs or Ah all represent battery charge.
The LTC4150’s transfer function is set only by the value
of the sense resistor and the gain G
selected using Equation 1, the charge per interrupt can
be determined from Equation 5 or 7.
Note that R
between ampere-hours of battery charge and number of
interrupts issued by the LTC4150. Rather, R
to keep the maximum sense voltage equal to or less than
the LTC4150’s 50mV full-scale sense input.
f = G
V
f = G
1Ah = 3600 Coulombs
1Ah = 3600 • G
One INT
One INT
SENSE
VF
VF
• ⏐V
• ⏐I
= I
SENSE
=
=
BATTERY
BATTERY
SENSE
G
3600 •
VF
SENSE
VF
is not chosen to set the relationship
⏐
•
• R
R
• R
1
• R
SENSE
G
VF
SENSE
across SENSE
VF
SENSE
SENSE
1
, where output frequency is the
•
R
Coulombs
SENSE
Interrupts
⏐
VF
[Ah]
+
. Once R
and SENSE
SENSE
is chosen
SENSE
–
. The
4150fc
(5)
(7)
(2)
(3)
(4)
(6)
(8)
is