LT8697
applicaTions inForMaTion
Cable Drop Compensation Over a Wide ꢂemperature
Range
See Table 1 for a list of copper wire resistances vs gauge.
ꢂable 1. Copper Wire Resistance vs Wire Gauge
Cable drop compensation with zero temperature variation
may be used in many applications. However, matching
the cable drop compensation temperature variation to the
cable resistance temperature variation may result in bet-
ter overall output voltage accuracy over a wide operating
temperature range. For example, in an application with
0.26Ω of wire resistance and a maximum output current
of 2.1A, cable drop compensation adds 0.55V at 25°C to
the output at max load for a fully compensated wire re-
sistance. If the wire in this example is copper, the copper
resistance temperature coefficient of about 4000ppm/°C
results in an output voltage error of –130mV at 85°C and
55mV at 0°C. Figure 2a shows this behavior.
AWG
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
RESISꢂANCE Oꢁ Cu WIRE Aꢂ 20°C (mΩ/m)
10.4
13.2
16.6
21.0
26.4
33.3
42.0
53.0
66.8
84.2
106
134
169
5.8
I
= 2.1A
LOAD
213
CABLE = 4 METERS AWG
20 TWISTED-PAIR COPPER
268
5.6
5.4
5.2
V
OUT
339
427
538
679
V
856
LOAD
5.0
4.8
1080
1360
1720
2160
2730
3440
–20
20
40
60
80
100
0
TEMPERATURE (°C)
8697 F02a
ꢁigure 2a. Cable Drop Compensation ꢂhrough 4m of AWG 20
ꢂwisted-Pair Cable (260mΩ) without ꢂemperature Compensation
Cable drop compensation can be made to vary positively
versus temperature with the addition of a negative tem-
perature coefficient (NTC) resistor as a part of the RCBL
resistance. This circuit idea assumes the NTC resistor is
at the same temperature as the cable. Figure 2b shows
RCBL
10k
1%
MURATA
10k
an example resistor network for R
that matches cop-
CBL
NCP21XV103J03RA
1%
per resistance variation over a wide –40°C to 125°C
temperature range. Figure 2c shows the resultant cable
drop compensation output at several temperatures using
RCBL with negative temperature variation.
10k THERMISTOR
8697 F02b
ꢁigure 2b. RCBL Resistor Network for Matching
Copper Wire ꢂemperature Coefficient
8697p
13
For more information www.linear.com/LT8697
LINEAR_DIMENSIONS [ Linear Dimensions ]
