OMO ElectronicOMO Electronic
Expand menu
Hello, Sign inMy Account
0 Cart

LT6600CDF-10#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
LT6600-10
10
66001fe
APPLICATIONS INFORMATION
Figure 5, present the output of the LT6600-10 with a 1600
differential load, or the equivalent of 800 to ground at
each output. The impedance seen by the network analyzer
input is still 50, reducing refl ections in the cabling be-
tween the transformer and analyzer input.
voltage of V
MID
. While the internal 11k resistors are well
matched, their absolute value can vary by ±20%. This
should be taken into consideration when connecting an
external resistor network to alter the voltage of V
MID
.
Figure 5. (S8 Pin Numbers)
–
+
0.1µF
0.1µF
2.5V
–2.5V
–
+
LT6600-10
3
4
1
7
2
8
5
6
6600 F05
402
402
NETWORK
ANALYZER
INPUT
50
COILCRAFT
TTWB-16A
4:1
NETWORK
ANALYZER
SOURCE
COILCRAFT
TTWB-1010
1:1
50
53.6
388
388
Figure 6
1MHz INPUT LEVEL (V
P-P
)
0
20
0
–20
–40
–60
–80
–100
–120
35
6600 F06
12
46
OUTPUT LEVEL (dBV)
3RD HARMONIC
85°C
1dB PASSBAND GAIN
COMPRESSION POINTS
1MHz 25°C
1MHz 85°C
3RD HARMONIC
25°C
2ND HARMONIC
25°C
2ND HARMONIC
85°C
Differential and Common Mode Voltage Ranges
The differential amplifi ers inside the LT6600-10 contain
circuitry to limit the maximum peak-to-peak differential
voltage through the fi lter. This limiting function prevents
excessive power dissipation in the internal circuitry
and provides output short-circuit protection. The limiting
function begins to take effect at output signal levels above
2V
P-P
and it becomes noticeable above 3.5V
P-P
. This is
illustrated in Figure 6; the LTC6600-10 was confi gured with
unity passband gain and the input of the fi lter was driven
with a 1MHz signal. Because this voltage limiting takes
place well before the output stage of the fi lter reaches the
supply rails, the input/output behavior of the IC shown
in Figure 6 is relatively independent of the power supply
voltage.
The two amplifi ers inside the LT6600-10 have independent
control of their output common mode voltage (see the
Block Diagram section). The following guidelines will
optimize the performance of the fi lter for single-supply
operation.
V
MID
must be bypassed to an AC ground with a 0.01µF or
higher capacitor. V
MID
can be driven from a low impedance
source, provided it remains at least 1.5V above V
–
and at
least 1.5V below V
+
. An internal resistor divider sets the
V
OCM
can be shorted to V
MID
for simplicity. If a different
common mode output voltage is required, connect V
OCM
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at V
OCM
must be less than or equal to
the mid-supply level. For example, voltage (V
OCM
) ≤1.65V
on a single 3.3V supply. For power supply voltages higher
than 3.3V the voltage at V
OCM
can be set above mid-supply.
The voltage on V
OCM
should not be more than 1V below
the voltage on V
MID
. The voltage on V
OCM
should not be
more than 2V above the voltage on V
MID
. V
OCM
is a high
impedance input.
The LT6600-10 was designed to process a variety of input
signals including signals centered around the mid-supply
voltage and signals that swing between ground and a
positive voltage in a single-supply system (Figure 1).
The range of allowable input common mode voltage (the
average of V
IN
+
and V
IN
–
in Figure 1) is determined by
the power supply level and gain setting (see the Electrical
Characteristics section).
Common Mode DC Currents
In applications like Figure 1 and Figure 3 where the
LT6600-10 not only provides lowpass fi ltering but also level
shifts the common mode voltage of the input signal, DC
LT6600-10
11
66001fe
APPLICATIONS INFORMATION
currents will be generated through the DC path between
input and output terminals. Minimize these currents to
decrease power dissipation and distortion.
Consider the application in Figure 3. V
MID
sets the output
common mode voltage of the 1st differential amplifi er
inside the LT6600-10 (see the Block Diagram section) at
2.5V. Since the input common mode voltage is near 0V, there
will be approximately a total of 2.5V drop across the series
combination of the internal 402 feedback resistor and the
external 100 input resistor. The resulting 5mA common
mode DC current in each input path, must be absorbed by
the sources V
IN
+
and V
IN
–
. V
OCM
sets the common mode
output voltage of the 2nd differential amplifi er inside the
LT6600-10, and therefore sets the common mode output
voltage of the fi lter. Since in the example, Figure 3, V
OCM
differs from V
MID
by 0.5V, an additional 2.5mA (1.25mA
per side) of DC current will fl ow in the resistors coupling
the 1st differential amplifi er output stage to fi lter output.
Thus, a total of 12.5mA is used to translate the common
mode voltages.
A simple modifi cation to Figure 3 will reduce the DC
common mode currents by 36%. If V
MID
is shorted to
V
OCM
the common mode output voltage of both op amp
stages will be 2V and the resulting DC current will be
8mA. Of course, by AC-coupling the inputs of Figure 3,
the common mode DC current can be reduced to 2.5mA.
Noise
The noise performance of the LT6600-10 can be evaluated
with the circuit of Figure 7.
Given the low noise output of the LT6600-10 and the 6dB
attenuation of the transformer coupling network, it will
be necessary to measure the noise fl oor of the spectrum
analyzer and subtract the instrument noise from the fi lter
noise measurement.
Example: With the IC removed and the 25 resistors
grounded, measure the total integrated noise (e
S
) of the
spectrum analyzer from 10kHz to 10MHz. With the IC
inserted, 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 LT6600-10 with R
IN
= 402 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
4 100 24V
RMS
–149
2 200 34V
RMS
–146
1 402 56V
RMS
–142
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.
Figure 7. (S8 Pin Numbers)
–
+
0.1µF
0.1µF
2.5V
–2.5V
–
+
LT6600-10
3
4
1
7
2
8
5
6
R
IN
R
IN
25
25
6600 F07
SPECTRUM
ANALYZER
INPUT
50
V
IN
COILCRAFT
TTWB-1010
1:1
LT6600-10
12
66001fe
APPLICATIONS INFORMATION
Power Dissipation
The LT6600-10 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 LT6600-10 S8 package has Pin 6 fused to the
lead frame to enhance thermal conduction when connect-
ing 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 copper, a
total of 660 square millimeters connected to Pin 6 of the
LT6600-10 S8 (330 square millimeters on each side of the
PC board) will result in a thermal resistance, θ
JA
,of about
85°C/W. Without the 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. LT6600-10 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
Junction temperature, T
J
, is calculated from the ambient
temperature, T
A
, and power dissipation, P
D
. The power
dissipation is the product of supply voltage, V
S
, and
supply current, I
S
. Therefore, the junction temperature
is given by:
T
J
= T
A
+ (P
D
• θ
JA
) = T
A
+ (V
S
• I
S
• θ
JA
)
where the supply current, I
S
, is a function of signal level, load
impedance, temperature and common mode voltages.
For a given supply voltage, the worst-case power dis-
sipation occurs when the differential input signal is
maximum, the common mode currents are maximum
(see the
Applications Information section regarding com-
mon mode DC currents), the load impedance is small and
the ambient temperature is maximum. To compute the
junction temperature, measure the supply current under
these worst-case conditions, estimate the thermal resis-
tance from Table 2, then apply the equation for T
J
. For
example, using the circuit in Figure 3 with DC differential
input voltage of 250mV, a differential output voltage of 1V,
no load resistance and an ambient temperature of 85°C,
the supply current (current into V
+
) measures 48.9mA.
Assuming a PC board layout with a 35mm
2
copper trace,
the θ
JA
is 100°C/W. The resulting junction temperature is:
T
J
= T
A
+ (P
D
• θ
JA
) = 85 + (5 • 0.0489 • 100) = 109°C
When using higher supply voltages or when driving small
impedances, more copper may be necessary to keep T
J
below 150°C.
Figure 8
FREQUENCY (MHz)
0.1
SPECTRAL DENSITY (nV
RMS
/√Hz)
INTEGRATED NOISE (mV
RMS
)
35
30
25
20
15
10
5
0
140
120
100
80
60
40
20
0
1.0 10 100
6600 F08
SPECTRAL DENSITY
INTEGRATED
NOISE
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LT6600CDF-10#TRPBF

Mfr. #:
Buy LT6600CDF-10#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
Differential Amplifiers Very L N, Diff Amp & 10MHz Lpass Filt
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet