Datasheet

LT6110
25
6110fa
For more information www.linear.com/LT6110
Case 1: LT6110 and the wire are at 75°C and the V
LOAD
error is –0.36%. If the R
SENSE
temperature coefficient
matches the wire’s temperature coefficient of 3900ppm/°C
then the V
LOAD
error is reduced. Using the copper wire
resistance of an inductor as an R
SENSE
external the V
LOAD
error is reduced to –0.025%.
Case 2: The LT6110 is at 75°C, the wire is at 25°C and the
V
LOAD
error is 2.3%. The 2.3% error is mostly due to the
internal R
SENSE
temperature coefficient. Using an external
±100ppm/°C R
SENSE
reduces the V
LOAD
error to ±0.05%.
In addition, using a thermistor across R
IN
to increase the
IOUT current as the temperature increases can reduce the
temperature induced V
LOAD
error.
Case 3: The LT6110 is at 25°C, the wire is at 75°C and the
V
LOAD
error is –2.6%. The error is due only to the copper
wire resistance increase vs temperature. The Case 3 error
can be reduced by designing for the maximum R
WIRE
at
a specified temperature. Copper wire specifications from
a reliable manufacturer are required.
The maximum current per wire is a function of the wire
temperature rise due to current, the maximum wire insula
-
tion temperature
and the number of cable wires (refer to
the Copper Wire Information section).
Table 4 is a random list of AWG wire resistance versus
current based on lab measurements.
applicaTions inForMaTion
Copper Wire Information
The wire used in the power distribution of electronic sys-
tems is
annealed (heated and cooled) copper wire and is
specified
for its resistance per unit length, weight per unit
mass and current capacity. In the American Wire Gauge
standard, AWG is the gauge number and corresponds to
the diameter of a solid wire (as the gauge number increases
the wire diameter decreases, the wire resistance increases
and the current capacity decreases). Stranded copper
wire is an insulated bundle of packed and twisted bare
solid strands and its resistance, weight or cost depends
on the type of coating (tin, silver or nickel) and stranding
options (how the strands are grouped and twisted). The
stranded wire’s flexibility is useful for building and rout
-
ing wire harness. The current capacity of copper wire is
inversely proportional to its gauge number, number of
wire conductors and operating temperature (increasing
gauge, conductors and temperature, decreases current
capacity). In addition the wire insulation temperature rat
-
ing determines
the maximum operating current (typical
insulation ratings range from 80°C to 200°C).
Copper
wire resistance increases directly with operating
temperature. The temperature coefficient of copper α is
equal to 0.0039/°C at 20°C (a useful linear approxima
-
tion from 0°
C to 100°C). If R
LOW
is the resistance at a
T
LOW
temperature and R
HIGH
is the resistance at a T
HIGH
Table 4. A Random List of Wire Resistance vs Current at 20°C
AWG 18
STRANDS/GAUGE
16/30
AWG 20
STRANDS/GAUGE
7/28
AWG 22
STRANDS/GAUGE
7/30
AWG 24
STRANDS/GAUGE
19/36
AWG 26
STRANDS/GAUGE
19/38
AWG 28
STRANDS/GAUGE
7/36
AWG 30
STRANDS/GAUGE
7/38
Current
(AMPS)
R
WIRE
(mΩ/ft)
R
WIRE
(mΩ/ft)
R
WIRE
(mΩ/ft)
R
WIRE
(mΩ/ft)
R
WIRE
(mΩ/ft)
R
WIRE
(mΩ/ft)
R
WIRE
(mΩ/ft)
1 6.53 9.61 15.42 22.47 37.97 62.31 102.36
2 6.54 9.63 15.51 22.66 38.41 63.32 109.14
3 6.56 9.68 15.66 22.99 39.08 65.23
4 6.59 9.73 15.84 23.38 40.21
5 6.62 9.82 15.99 23.78
6 6.65 9.90 16.32
7 6.71 10.02
8 6.79 10.15
9 6.83
10 6.91