LT6600-5
10
66005fb
APPLICATIONS INFORMATION
Example: With the IC removed and the 25 resistors
grounded, measure the total integrated noise (e
S
) of the
spectrum analyzer from 10kHz to 5MHz. With the IC in-
serted, the signal source (V
IN
) disconnected, and the input
resistors grounded, measure the total integrated noise
out of the fi lter (e
O
). With the signal source connected,
set the frequency to 1MHz and adjust the amplitude until
V
IN
measures 100mV
P-P
. Measure the output amplitude,
V
OUT
, and compute the passband gain A = V
OUT
/V
IN
. Now
compute the input referred integrated noise (e
IN
) as:
e
IN
=
(e
O
)
2
–(e
S
)
2
A
Table 1 lists the typical input referred integrated noise for
various values of R
IN
.
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6600-5 with R
IN
= 806 and 200
using the fi xture of Figure 7 (the instrument noise has
been subtracted from the results).
Table 1. Noise Performance
PASSBAND
GAIN (V/V) R
IN
INPUT REFERRED
INTEGRATED NOISE
10kHz TO 10MHz
INPUT REFERRED
NOISE dBm/Hz
4 200 24µV
RMS
–149
2 402 38µV
RMS
–145
1 806 69µV
RMS
–140
The noise at each output is comprised of a differential
component and a common mode component. Using a
transformer or combiner to convert the differential outputs
to single-ended signal rejects the common mode noise and
gives a true measure of the S/N achievable in the system.
Conversely, if each output is measured individually and the
noise power added together, the resulting calculated noise
level will be higher than the true differential noise.
Power Dissipation
The LT6600-5 amplifi ers combine high speed with large-
signal currents in a small package. There is a need to
ensure that the dies’s junction temperature does not
exceed 150°C. The LT6600-5 package has Pin 6 fused
to the lead frame to enhance thermal conduction when
connecting to a ground plane or a large metal trace. Metal
trace and plated through-holes can be used to spread the
heat generated by the device to the backside of the PC
board. For example, on a 3/32" FR-4 board with 2oz cop-
per, a total of 660 square millimeters connected to Pin 6
of the LT6600-5 (330 square millimeters on each side of
the PC board) will result in a thermal resistance, θ
JA
, of
about 85°C/W. Without extra metal trace connected to the
V
–
pin to provide a heat sink, the thermal resistance will
be around 105°C/W. Table 2 can be used as a guide when
considering thermal resistance.
Table 2. LT6600-5 SO-8 Package Thermal Resistance
COPPER AREA
TOPSIDE
(mm
2
)
BACKSIDE
(mm
2
)
BOARD AREA
(mm
2
)
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
1100 1100 2500 65°C/W
330 330 2500 85°C/W
35 35 2500 95°C/W
35 0 2500 100°C/W
0 0 2500 105°C/W
Figure 7
Figure 8
–
+
0.1µF
0.1µF
2.5V
–2.5V
–
+
LT6600-5
3
4
1
7
2
8
5
6
R
IN
R
IN
25Ω
25Ω
66005 F07
SPECTRUM
ANALYZER
INPUT
50Ω
V
IN
COILCRAFT
TTWB-1010
1:1
FREQUENCY (MHz)
0.01
NOISE DENSITY (nV/√Hz)
INTEGRATED NOISE (µV)
100
45
40
35
30
25
20
15
10
5
0
90
80
70
60
50
40
30
20
10
0
66005 G08
0.1 10
INTEGRATED NOISE, GAIN = 1X
INTEGRATED NOISE, GAIN = 4X
NOISE DENSITY, GAIN = 1X
NOISE DENSITY, GAIN = 4X
