LTC6102CDD LINER [Linear Technology], LTC6102CDD Datasheet - Page 9

• Manufacturer Part Number: LTC6102CDD
• Description: Precision Zero Drift Current Sense Amplifi er
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
This is the same value as the input offset. A larger sense
resistor will reduce the error due to offset by increasing
the sense voltage for a given load current.
For this example, choosing a 5mΩ R
the dynamic range and provide a system that has 100mV
across the sense resistor at peak load (20A), while input
offset causes an error equivalent to only 0.6mA of load
current.
Peak dissipation is 2W. If a 0.5mΩ sense resistor is em-
ployed, then the effective current error is 6mA (0.03%
of full-scale), while the peak sense voltage is reduced to
10mV at 20A, dissipating only 200mW.
The low offset and corresponding large dynamic range of
the LTC6102 make it more fl exible than other solutions
in this respect. The 3μV typical offset gives 100dB of dy-
namic range for a sense voltage that is limited to 300mV
max, and over 116dB of dynamic range if a maximum of
2V is allowed.
The previous example assumes that a large output dynamic
range is required. For circuits that do not require large
dynamic range, the wide input range of the LTC6102 may
be used to reduce the size of the sense resistor, reducing
power loss and increasing reliability. For example, in a
100A circuit requiring 60dB of dynamic range, the input
offset and drift of most current-sense solutions will require
that the shunt be chosen so that the sense voltage is at
least 100mV at full scale so that the minimum input is
greater than 100μV. This will cause power dissipation in
excess of 10W at full scale! That much power loss can put
a signifi cant load on the power supply and create thermal
design headaches. In addition, heating in the sense resistor
can reduce its accuracy and reliability.
In contrast, the large dynamic range of the LTC6102 allows
the use of a much smaller sense resistor. The LTC6102
allows the minimum sense voltage to be reduced to less
than 10μV. The peak sense voltage would then be 10mV,
dissipating only 1W at 100A in a 100μΩ sense resistor!
With a specialized sense resistor, the same system would
allow peak currents of more than 1000A without exceeding
the input range of the LTC6102 or damaging the shunt.
SENSE
will maximize
Sense Resistor Connection
Kelvin connection of +IN and –INS to the sense resistor
should be used in all but the lowest power applications.
Solder connections and PC board interconnections that
carry high current can cause signifi cant error in measure-
ment due to their relatively large resistances. One 10mm
× 10mm square trace of one-ounce copper is approxi-
mately 0.5mΩ. A 1mV error can be caused by as little
as 2A fl owing through this small interconnect. This will
cause a 1% error in a 100mV signal. A 10A load current
in the same interconnect will cause a 5% error for the
same 100mV signal. An additional error is caused by the
change in copper resistance over temperature, which is in
excess of 0.4%/°C. By isolating the sense traces from the
high-current paths, this error can be reduced by orders of
magnitude. A sense resistor with integrated Kelvin sense
terminals will give the best results. Figure 2 illustrates the
recommended method. Note that the LTC6102 has a Kelvin
input structure such that current fl ows into –INF . The –INS
and –INF pins should be tied as close as possible to R
This reduces the parasitic series resistance so that R
may be as low as 1Ω, allowing high gain settings to be
used with very little gain error.
110
100
90
80
70
60
50
40
30
20
0.001
Dynamic Range vs Maximum
Power Dissipation in R
DYNAMIC RANGE RELATIVE
TO 10μV, MINIMUM V
LTC6102/LTC6102HV
R
100dB: MAX
V
SENSE
SENSE
MAXIMUM POWER DISSIPATION (W)
R
MAX I
MAX I
MAX I
SENSE
0.01
= 1V
= 1mΩ
R
SENSE
SENSE
SENSE
SENSE
= 1Ω
R
SENSE
0.1
= 100mΩ
= 1A
= 10A
= 100A
SENSE
= 100μΩ
1
R
SENSE
R
SENSE
40dB: MAX
V
SENSE
SENSE
= 10μΩ
10
= 10mΩ
= 1mV
6102 F10
100
6102fb
9
IN
IN
.