LT6105
16
6105fa
Output Filtering
The output voltage, V
OUT
is simply I
OUT
• Z
OUT
. This
makes fi ltering straightforward. Any circuit may be used
which generates the required Z
OUT
to get the desired fi lter
response. For example, a capacitor in parallel with R
OUT
will give a low pass 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 an ADC. This output capacitor
in parallel with an output resistor will create a pole in the
output response at:
f
RC
db
OUT OUT
–
•• •
3
1
2
=
π
APPLICATIONS INFORMATION
Response Time
The LT6105 is designed to exhibit fast response to inputs
for the purpose of circuit protection or signal transmission.
This response time will be affected by the external circuit
in two ways—delay and speed. If the output current is
very low and an input transient occurs, there may be an
increased delay before the output voltage begins changing.
This can be improved by increasing the minimum output
current, either by increasing R
SENSE
or decreasing R
IN
. The
effect of increased output current is illustrated in the step
response curves in the Typical Performance Characteristics
section of this data sheet. Note that the curves are labeled
with respect to the initial output currents. The speed is
also affected by the external circuit. In this case, if the
input changes very quickly, the internal amplifi er will slew
the base of the internal output PNP (Figure 1) in order to
maintain the internal loop. This results in current fl owing
through R
IN
and the internal PNP. This current slew rate
will be determined by the amplifi er and PNP characteris-
tics as well as the input resistor, R
IN
. See the Slew Rate
vs R
IN
curve in the Typical Performance Characteristics
section. Using a smaller R
IN
will allow the output current
to increase more quickly, decreasing the response time
at the output. This will also have the effect of increasing
the maximum output current.
–
+
0.039Ω
249Ω
249Ω
4.99k
LT6105
TO LOAD
SOURCE
0V TO 44V
V
OUT
= 780mV/A
V
OUT
0.22μF
6105 TA02
2.85V TO 36V
V
S
+
V
S
–
–IN
+IN
V
–
V
+
Gain of 20 Current Sense Amplifi er with Output Filtering
TYPICAL APPLICATIONS
