LTC6102CDD LINER [Linear Technology], LTC6102CDD Datasheet - Page 10

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

APPLICATIONS INFORMATION
LTC6102/LTC6102HV
Selection of External Input Resistor, R
The external input resistor, R
tance of the current sense circuit, I
example, if R
1mA for V
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 (Note 1) 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 output current and power dis-
sipation. If small sense currents must be resolved ac-
curately in a system that has very wide dynamic range, a
smaller R
10
OUT
IN
should be chosen to provide the required resolution
R
may be as much as 1mA. By setting R
Figure 2. Kelvin Input Connection Preserves Accuracy
with Large Load Current and Large Output Current
SENSE
OUTPUT
LOAD
IN
V
SENSE
+
R
may be used if the max current is limited in
OUT
IN
R
R
IN
IN
V
–
+
= 100, then I
–
= 100mV.
+IN
V
V
+
–
*VISHAY VCS1625 SERIES
WITH 4 PAD KELVIN CONNECTION
LTC6102
R
IN
TIE AS CLOSE TO R
+
–
LTC6102
R
IN
SENSE
OUT
–
, controls the transconduc-
*
= V
IN
OUT
R
AS POSSIBLE
IN
V
SENSE
–INS
V
OUT
–INF
V
LOAD
–
REG
+
+
C
IN
REG
= V
IN
can be increased
OUT
R
/100 or I
SENSE
OUT
6102 F02
IN
= 1mA, then
V
OUT
such that
0.1μF
/R
IN
OUT
. For
=
another way, such as with a Schottky diode across R
(Figure 3). 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.
Care should be taken when designing the PC board lay-
out for R
interconnect impedances will increase the effective R
value, causing a gain error. It is important to note that the
large temperature drift of copper resistance will cause a
change in gain over temperature if proper care is not taken
to reduce this effect.
To further limit the effect of trace resistance on gain,
maximizing the accuracy of these circuits, the LTC6102 has
been designed with a Kelvin input. The inverting terminal
(–INS) is separate from the feedback path (–INF). During
operation, these two pins must be connected together.
The design of the LTC6102 is such that current into –INS
is input bias current only, which is typically 60pA at 25°C.
Almost all of the current from R
the LTC6102, and into R
minimize gain error, –INS should be routed in a separate
path from –INF to a point as close to R
addition, the higher potential terminal of R
connected directly to the positive terminal of R
any input voltage source). For the highest accuracy, R
should be a four-terminal resistor if it is less than 10Ω.
Selection of External Output Resistor, R
The output resistor, R
rent is converted to voltage. V
In choosing an output resistor, the max output voltage
must fi rst be considered. If the circuit that is driven by the
output does not have a limited input voltage, then R
Figure 3. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
IN
, especially for small R
R
SENSE
OUT
LOAD
V
+
, determines how the output cur-
OUT
6102 F03
via the OUT pin. In order to
OUT
IN
D
SENSE
fl ows into –INF , through
IN
is simply I
values. All trace and
IN
OUT
as possible. In
IN
OUT
should be
SENSE
• R
SENSE
OUT
6102fb
OUT
(or
IN
IN
.