LT6604-5
9
66045fa
APPLICATIONS INFORMATION
–
+
806Ω
0.01μF
0.1μF
3.3V
–
+
VIN
–
VIN
+
66045 F01
VOUT
+
VOUT
–
V
t
3
2
1
VIN
+
VIN
–
V
t
3
2
1
VOUT
+
1/2
LT6604-5
VOUT
–
0
25
27
4
34
6
2
29
7
–
+
806Ω
0.01μF
0.1μF
3.3V
–
+
VIN
+
66045 F02
VOUT
+
VOUT
–
V
3
2
1
t
0
VOUT
+
VOUT
–
2
V
t
1
0
–1
VIN
+
25
27
4
34
6
2
29
7
1/2
LT6604-5
–
+
200Ω
0.1μF
0.01μF
5V
–
+
VIN
–
VIN
+
25
27
4
34
6
2
29
7
66045 F03
VOUT
+
VOUT
–
+
– 2V
V
t
3
2
1
0
VOUT
+
VOUT
–
V
t
3
2
1
0
VIN
+
VIN
–
500mVP-P (DIFF)
62pF
1/2
LT6604-5
Figure 1
Figure 2
Figure 3
Interfacing to the LT6604-5
Note: The LT6604-5 contains two identical lters. The fol-
lowing applications information only refers to one lter.
The two lters are independent except that they share the
same negative supply voltage V–. The two lters can be
used simultaneously by replicating the example circuits.
The referenced pin numbers correspond to the A channel
lter.
Each LT6604-5 channel requires two equal external re-
sistors, RIN, to set the differential gain to 806Ω/RIN. The
inputs to the lter are the voltages VIN+ and VIN– presented
to these external components, Figure 1. The difference
between VIN+ and VIN– is the differential input voltage.
The average of VIN+ and VIN– is the common mode input
voltage. Similarly, the voltages VOUT+ and VOUT– appearing
at Pins 27 and 29 of the LT6604-5 are the lter outputs.
The difference between VOUT+ and VOUT– is the differential
output voltage. The average of VOUT+ and VOUT– is the com-
mon mode output voltage. Figure 1 illustrates the LT6604-5
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
2VP-P. The common mode output voltage is 1.65V, and the
differential output voltage is 2VP-P for frequencies below
5MHz. The common mode output voltage is determined
by the voltage at VOCM. Since VOCM is shorted to VMID,
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 VMID.
Figure 2 shows how to AC couple signals into the LT6604-5.
In this instance, the input is a single-ended signal. AC-cou-
pling allows the processing of single-ended or differential
signals with arbitrary common mode levels. The 0.1μF
coupling capacitor and the 806Ω gain setting resistor form
a high pass lter, attenuating signals below 2kHz. Larger
values of coupling capacitors will proportionally reduce
this highpass 3dB frequency.
In Figure 3 the LT6604-5 is providing 12dB of gain. The
gain resistor has an optional 62pF in parallel to improve
the passband atness near 5MHz. The common mode
output voltage is set to 2V.