LT6600-2.5
APPLICATIO S I FOR ATIO
Interfacing to the LT6600-2.5
The LT6600-2.5 requires two equal external resistors, R
IN
,
to set the differential gain to 1580Ω/R
IN
. The inputs to the
filter are the voltages V
IN+
and V
IN–
presented to these
external components, Figure 1. The difference between
V
IN+
and V
IN–
is the differential input voltage. The average
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 filter outputs. The
difference 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
V
3
2
1
0
V
IN+
+
V
IN
V
IN
–
1580Ω
V
IN–
t
1580Ω
V
0.1µF
2
1
0
–1
V
IN+
0.1µF
t
V
IN
+
V
3
2
1
0
500mV
P-P
(DIFF)
V
IN+
V
IN–
t
0.01µF
V
IN
+
V
IN
–
6
U
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 pin 2.
Since pin 2 is shorted to pin 7, 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
Pin 7.
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 0.1µF coupling capacitor and the 1580Ω gain setting
resistor form a high pass filter, attenuating signals below
1kHz. Larger values of coupling capacitors will propor-
tionally reduce this highpass 3dB frequency.
3.3V
0.1µF
1
7
0.01µF
2
8
3
V
3
W
U U
–
LT6600-2.5
+
4
V
OUT
+
2
1
0
V
OUT+
V
OUT–
t
660025 F01
+
6
–
5
V
OUT–
Figure 1
3.3V
0.1µF
1580Ω
1
7
0.01µF
1580Ω
2
8
3
V
3
V
OUT+
V
OUT–
2
1
0
V
OUT+
V
OUT–
–
LT6600-2.5
+
4
+
6
–
5
660025 F02
Figure 2
5V
0.1µF
402Ω
1
7
2
8
3
V
3
V
OUT+
2
V
OUT–
1
0
V
OUT–
V
OUT+
–
LT6600-2.5
+
4
+
6
–
5
402Ω
+
–
2V
t
660025 F03
Figure 3
660025i
LINER [ LINEAR TECHNOLOGY ]
