LTC6103 Linear Integrated Systems, LTC6103 Datasheet - Page 8

• Manufacturer Part Number: LTC6103
• Description: High Side Current Sense Amplifier
• Manufacturer: Linear Integrated Systems

APPLICATIONS INFORMATION
LTC6103
Sense Resistor Connection
Kelvin connections should be used between the inputs (+IN
and –IN) and the sense resistor in all but the lowest power
applications. Solder connections and PC board intercon-
nections that carry high current can cause signifi cant error
in measurement due to their relatively large resistances.
One 10mm × 10mm square trace of one-ounce copper
is approximately 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. 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.
Selection of External Input Resistor, R
The external input resistor, R
conductance of the current sense circuit. Since:
8
I
OUT
=
Figure 2. Kelvin Input Connection Preserves
Accuracy Despite Large Load Current
V
SENSE
R
IN
, transconductance g =
LOAD
I
1/2
LTC6103
LOAD
V
S
+ –
R
+IN
SENSE
R
OUT
OUT
V
+
R
–IN
IN
IN
, controls the trans-
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V
6103 F02
–
m
IN
R
1
IN
For example, if R
or I
R
while limiting the output current. At low supply voltage,
I
the largest expected sense voltage gives I
the maximum output dynamic range is available. Output
dynamic range is limited by both the maximum allowed
output current and the maximum allowed output voltage,
as well as the minimum practical output signal. If less
dynamic range is required, then R
accordingly, reducing the maximum output current and
power dissipation. If low sense currents must be resolved
accurately in a system that has very wide dynamic range,
a smaller R
allows may be used if the maximum current is limited in
another way, such as with a Schottky diode across R
(Figure 3a). This will reduce the high current measurement
accuracy by limiting the result, while increasing the low
current measurement resolution.
This approach can be helpful in cases where occasional
large burst currents may be ignored. It can also be used
in a multi-range confi guration where a low current circuit
is added to a high current circuit (Figure 3b). Note that a
comparator (LTC1540) is used to select the range, and
transistor M1 limits the voltage across R
Figure 3a. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
OUT
IN
I
OUT
OUT
should be chosen to allow the required resolution
may be as much as 1mA. By setting R
= 1mA for V
=
V
100Ω
SENSE
IN
than the maximum current specifi cation
IN
R
= 100Ω, then:
SENSE
SENSE
LOAD
V
+
= 100mV.
6103 F03a
D
SENSE
IN
can be increased
OUT
SENSE(LO)
IN
= 1mA, then
such that
.
SENSE
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