Datasheet

LT6600-2.5
8
660025fe
APPLICATIONS INFORMATION
Figure 1. (S8 Pin Numbers)
Interfacing to the LT6600-2.5
Note: The referenced pin numbers correspond to the S8
package. See the Pin Functions for the equivalent DFN-12
package pin numbers.
The LT6600-2.5 requires two equal external resistors, R
IN
,
to set the differential gain to 1580/R
IN
. The inputs to the
fi lter are the voltages V
IN
+
and V
IN
–
presented to the see
external components, Figure 1. The difference between
V
IN
+
and V
IN
–
is the differential input voltage. The aver-
age of V
IN
+
and V
IN
–
is the common mode input voltage.
Similarly, the voltages V
OUT
+
and V
OUT
–
appearing at Pins 4
and 5 of the LT6600-2.5 are the fi lter outputs. The differ-
ence between V
OUT
+
and V
OUT
–
is the differential output
voltage. The average of V
OUT
+
and V
OUT
–
is the common
mode output voltage.
Figure 1 illustrates the LT6600-2.5 operating with a single
3.3V supply and unity passband gain; the input signal is
DC-coupled. The common mode input voltage is 0.5V, and
the differential input voltage is 2V
P-P
. The common mode
output voltage is 1.65V, and the differential output voltage
is 2V
P-P
for frequencies below 2.5MHz. The common mode
output voltage is determined by the voltage at V
OCM
. Since
V
OCM
is shorted to V
MID
, the output common mode is the
mid-supply voltage. In addition, the common mode input
voltage can be equal to the mid-supply voltage of V
MID
.
Figure 2 shows how to AC couple signals into the LT6600-2.5.
In this instance, the input is a single-ended signal.
AC-coupling allows the processing of single-ended or
differential signals with arbitrary common mode levels.
The 0.1F coupling capacitor and the 1580 gain set-
ting resistor form a highpass fi lter, attenuating signals
below 1kHz. Larger values of coupling capacitors will
proportionally reduce this highpass 3dB frequency.
In Figure 3 the LT6600-2.5 is providing 12dB of gain. The
common mode output voltage is set to 2V.
Figure 2. (S8 Pin Numbers)
Figure 3. (S8 Pin Numbers)
–
+
1580Ω
1580Ω
0.01µF
0.1µF
3.3V
–
+
V
IN
–
V
IN
+
3
4
1
7
2
8
5
6
660025 F01
V
OUT
+
V
OUT
–
V
t
3
2
1
V
IN
+
V
IN
–
V
t
3
2
1
V
OUT
+
LT6600-2.5
V
OUT
–
0 0
–
+
1580
1580
0.01µF
0.1µF
0.1µF
0.1µF
3.3V
–
+
V
IN
+
3
4
1
7
2
8
5
6
660025 F02
V
OUT
+
V
OUT
–
V
3
2
1
t
0
LT6600-2.5
V
OUT
+
V
OUT
–
2
V
t
1
0
–1
V
IN
+
–
+
402Ω
402Ω
0.1µF
0.01µF
5V
–
+
V
IN
–
V
IN
+
3
4
1
7
2
8
5
6
660025 F03
V
OUT
+
V
OUT
–
+
–
2V
V
t
3
2
1
0
V
OUT
+
V
OUT
–
LT6600-2.5
V
t
3
2
1
0
V
IN
+
V
IN
–
500mV
P-P
(DIFF)