LTC6103

8

6103f

APPLICATIONS INFORMATION

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 significant error

in measurement due to their relatively large resistances.

One 10mm

× 10mm square trace of one-ounce copper

is approximately 0.5m

Ω. A 1mV error can be caused by

as little as 2A flowing 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.

conductance of the current sense circuit. Since:

I

V

R

OUT

SENSE

IN

=

, transconductance g

=

1

R

m

IN

I

V

OUT

SENSE

=

100

Ω

while limiting the output current. At low supply voltage,

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

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,

allows may be used if the maximum current is limited in

(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 configuration 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

Figure 2. Kelvin Input Connection Preserves

Accuracy Despite Large Load Current

Figure 3a. Shunt Diode Limits Maximum Input Voltage to Allow

Better Low Input Resolution Without Overranging

+

–

+IN

OUT

1/2

LTC6103

–IN

6103 F02

LOAD

LOAD

6103 F03a