LTC2942-1I View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC2942-1I
Linear Technology
'LTC2942-1I' PDF : 16 Pages View PDF
LTC2942-1
Applications Information
Measuring Current
In some applications, it may be desirable to measure the
current ISENSE flowing through the internal sense resistor.
Since charge measured by the coulomb counter is the
time integral over ISENSE, differentiation of the contents
of the accumulated charge register (ACR) over time may
be used to measure average current.
Accuracy of such an indirect current measurement is limited
by the basic accuracy of the coulomb counter, the accuracy
of the timebase within the host system, quantization caused
by the prescaler setting, and time delays caused by I2C
transactions. Still, especially at higher currents, useful
results may be obtained by reading the accumulated charge
register twice, with a defined time interval in between, and
dividing the charge difference by the time interval. The
time interval may be increased at low currents to limit time
quantization errors to the desired accuracy. For quicker
current measurements at low currents, prescale factor M
may be temporarily decreased, sacrificing some coulomb
count accuracy for higher current resolution.
Extending Coulomb Counter Range
To increase the range of the coulomb counter for battery
capacities higher than 5.5Ah, the host controller can either
regularly poll the accumulated charge register (ACR) or use
the threshold registers to determine when the accumulated
charge register approaches the minimum or maximum
limits. At this point it can add or subtract a fixed charge
quantity and rewrite the result into the ACR. The added
or subtracted charge quantities can then be tracked in
software, increasing the effective ACR range.
PC Board Layout Suggestions
Keep all traces as short as possible to minimize noise and
inaccuracy. Use wider traces from the resistor to the bat-
tery, load and/or charger (see Figure 11). Put the bypass
capacitor close to SENSE+ and GND. Provide adequate
copper area on exposed pad for heat sinking.
ELECTRICALLY ISOLATED HEAT SINK
TO
CHARGER/LOAD
C
1
6
2
LTC2942-1
5
3
4
TO BATTERY
CONNECTED TO EXPOSED PAD ONLY
29421 F11
Figure 11. Recommended Layout
Package Description
DCB Package
6-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-1715)
0.70 p0.05
2.00 p0.10
(2 SIDES)
R = 0.115
R = 0.05
TYP
TYP
4
0.40 p 0.10
6
3.55 p0.05
1.65 p0.05
(2 SIDES)
2.15 p0.05
PACKAGE
OUTLINE
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.25 p 0.05
0.50 BSC
1.35 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.200 REF
3.00 p0.10 1.65 p 0.10
(2 SIDES) (2 SIDES)
0.75 p0.05
0.00 – 0.05
PIN 1 NOTCH
R0.20 OR 0.25
s 45o CHAMFER
3
1
(DCB6) DFN 0405
0.25 p 0.05
0.50 BSC
1.35 p0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (TBD)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
29421f
15
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