LTC6103 データシートの表示（PDF） - Linear Technology
部品番号
コンポーネント説明
一致するリスト
LTC6103 Datasheet PDF : 16 Pages
| |||
LTC6103
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 0.5mΩ. 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.
Selection of External Input Resistor, RIN
The external input resistor, RIN, controls the trans-
conductance of the current sense circuit. Since:
IOUT
=
VSENSE ,
RIN
transconductance
gm
=
1
RIN
V+
ILOAD RSENSE
LOAD
RIN
+IN –IN
For example, if RIN = 100Ω, then:
IOUT
=
VSENSE
100Ω
or IOUT = 1mA for VSENSE = 100mV.
RIN should be chosen to allow the required resolution
while limiting the output current. At low supply voltage,
IOUT may be as much as 1mA. By setting RIN such that
the largest expected sense voltage gives IOUT = 1mA, then
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 RIN can be increased
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 RIN than the maximum current specification
allows may be used if the maximum current is limited in
another way, such as with a Schottky diode across RSENSE
(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
transistor M1 limits the voltage across RSENSE(LO).
VS
1/2
LTC6103
OUT
V–
ROUT
6103 F02
Figure 2. Kelvin Input Connection Preserves
Accuracy Despite Large Load Current
V+
RSENSE
DSENSE
6103 F03a
LOAD
Figure 3a. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
6103f
8
Share Link: 