LT6107
10
6107fc
For more information www.linear.com/LT6107
APPLICATIONS INFORMATION
power dissipation is 41mW. This amount of power dis-
sipation will result in a 10°C rise in junction temperature
above the ambient temperature.
It is important to note that the LT6107 has been designed
to provide at least 1mA to the output when required, and
can deliver more depending on the conditions. Care must
be taken to limit the maximum output current by proper
choice of sense resistor and R
IN
–
and, if input fault con-
ditions exist, external clamps.
Output Filtering
The output voltage, V
OUT
, is simply I
OUT
• Z
OUT
. This
makes filtering straightforward. Any circuit may be used
which generates the required Z
OUT
to get the desired filter
response. For example, a capacitor in parallel with R
OUT
will give a lowpass response. This will reduce unwanted
noise from the output, and may also be useful as a charge
reservoir to keep the output steady while driving a switch-
ing circuit such as a MUX or ADC. This output capacitor
in parallel with an output resistor will create a pole in the
output response at:
f
–3dB
1
2 • • R
• C
Useful Equations
Input Voltage: V
SENSE
I
SENSE
• R
SENSE
Voltage Gain:
V
OUT
V
R
OUT
R
Current Gain:
I
OUT
I
SENSE
R
SENSE
R
IN
Transconductance:
I
OUT
V
SENSE
1
R
IN
Transimpedance:
V
OUT
I
R
SENSE
•
R
OUT
R
IN
Power Supply Connection
For normal operation, the V
+
pin should be connected to
either side of the sense resistor. Either connection will
meet the constraint that +IN ≤ V
+
and –IN ≤ V
+
. During
normal operation, V
SENSE
should not exceed 500mV (see
V
SENSE(MAX)
under Electrical Characteristics). This addi-
tional constraint can be stated as V
+
– (+IN) ≤ 500mV.
Referring to Figure 5, feedback will force the voltages
at the inputs –IN and +IN to be equal to (V
S
– V
SENSE
).
Connecting V
+
to the load side of the shunt results in equal
voltages at +IN, –IN and V
+
. Connecting V
+
to the supply
end of the shunt results in the voltages at +IN and –IN to
be V
SENSE
below V
+
.
If the V
+
pin is connected to the supply side of the shunt
resistor, the supply current drawn by the LT6107 is not
included in the monitored current. If the V
+
pin is con-
nected to the load side of the shunt resistor (Figure 5),
the supply current drawn by the LT6107 is included in
the monitored current. It should be noted that in either
configuration, the output current of the LT6107 will not
be monitored since it is drawn through the R
IN
resistor
connected to the positive side of the shunt. Contact the
factory for operation of the LT6107 with a V
+
outside of
the recommended operating range.
Figure 5. LT6107 Supply Current Monitored with the Load
Reverse Supply Protection
Some applications may be tested with reverse-polarity
supplies due to an expectation of the type of fault during
operation. The LT6107 is not protected internally from
external reversal of supply polarity. To prevent damage
that may occur during this condition, a Schottky diode
should be added in series with V
–
(Figure 6). This will
limit the reverse current through the LT6107. Note that
this diode will limit the low voltage performance of the
LT6107 by effectively reducing the supply voltage to the
part by V
D
.
LT6107
R
OUT
V
OUT
6107 F05
R
IN
V
S
LOAD
R
SENSE
–
+
V
+
V
–
OUT
–IN+IN
