LT6604CUFF-5-PBF LINER [Linear Technology], LT6604CUFF-5-PBF Datasheet - Page 12

• Manufacturer Part Number: LT6604CUFF-5-PBF
• Description: Dual Very Low Noise, Differential Amplifi er and 5MHz Lowpass Filter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LT6604-5
(e
the IC inserted, the signal source (V
the input resistors grounded, measure the total integrated
noise out of the fi lter (e
set the frequency to 1MHz and adjust the amplitude until
V
V
compute the input referred integrated noise (e
Table 1 lists the typical input referred integrated noise for
various values of R
Table 1. Noise Performance
PASSBAND
GAIN
4
2
1
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6604-5 with R
fi xture of Figure 7 (the instrument noise has been sub-
tracted from the results).
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
12
IN
OUT
S
e
) of the spectrum analyzer from 10 kHz to 5MHz. With
measures 100mV
IN
, and compute the passband gain A = V
=
V
IN
( ) – ( )
e
R
200Ω
402Ω
806Ω
O
IN
R
R
2
IN
IN
A
34
4
6
2
IN
e
S
+
–
1/2
LT6604-5
.
25
INPUT REFERRED
INTEGRATED NOISE
10kHz TO 5MHz
24μV
38μV
69μV
O
P-P
–2.5V
7
2.5V
). With the signal source connected,
2
+
–
. Measure the output amplitude,
Figure 7
0.1μF
0.1μF
RMS
RMS
RMS
27
29
25Ω
25Ω
IN
IN
COILCRAFT
TTWB-1010
) disconnected, and
= 806Ω using the
INPUT REFERRED
NOISE dBm/Hz
–149
–145
–140
1:1
OUT
SPECTRUM
ANALYZER
IN
/V
INPUT
) as:
IN
66045 F07
50Ω
. Now
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 LT6604-5 amplifi ers combine high speed with large
signal currents in a small package. There is a need to en-
sure that the die’s junction temperature does not exceed
150°C. The LT6604-5 has an exposed pad (pin 35) which
is connected to the lower supply (V
to a ground plane helps to dissipate the heat generated
by the chip. Metal trace and plated through-holes can be
used to spread the heat generated by the device to the
backside of the PC board.
Junction temperature, T
temperature, T
dissipation is the product of supply voltage, V
supply current, I
given by:
where the supply current, I
load impedance, temperature and common mode voltages.
For a given supply voltage, the worst-case power dissipation
occurs when the differential input signal is maximum, the
common mode currents are maximum (see Applications
T
J
= T
A
+ (P
45
40
35
30
25
20
15
10
5
0
0.01
D
A
Figure 8. Input Referred Noise
, and power dissipation, P
S
• θ
. Therefore, the junction temperature is
INTEGRATED NOISE, GAIN = 1X
INTEGRATED NOISE, GAIN = 4X
NOISE DENSITY, GAIN = 1X
NOISE DENSITY, GAIN = 4X
JA
0.1
) = T
FREQUENCY (MHz)
J
, is calculated from the ambient
A
S
+ (V
, is a function of signal level,
1
S
• I
–
). Connecting the pad
10
S
• θ
66045 F08
JA
)
100
D
90
80
70
60
50
40
30
20
10
0
. The power
S
, and total
66045f