600I25 [Linear]
Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter; 非常低噪声,差分放大器和2.5MHz的低通滤波器型号: | 600I25 |
厂家: | Linear |
描述: | Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter |
文件: | 总12页 (文件大小:169K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
Final Electrical Specifications
LT6600-2.5
Very Low Noise, Differential
Amplifier and 2.5MHz Lowpass Filter
June 2003
U
FEATURES
DESCRIPTIO
Programmable Differential Gain via Two External
The LT®6600-2.5 combines a fully differential amplifier
with a 4th order 2.5MHz lowpass filter approximating a
Chebyshev frequency response. Most differential amplifi-
ers require many precision external components to tailor
gain and bandwidth. In contrast, with the LT6600-2.5, two
externalresistorsprogramdifferentialgain, andthefilter’s
2.5MHz cutoff frequency and passband ripple are inter-
nallyset.TheLT6600-2.5alsoprovidesthenecessarylevel
shifting to set its output common mode voltage to accom-
modate the reference voltage requirements of A/Ds.
■
Resistors
■
Adjustable Output Common Mode Voltage
■
Operates and Specified with 3V, 5V, ±5V Supplies
■
0.5dB Ripple 4th Order Lowpass Filter with 2.5MHz
Cutoff
■
86dB S/N with 3V Supply and 1VRMS Output
■
Low Distortion, 1VRMS, 800Ω Load
1MHz: 95dBc 2nd, 88dBc 3rd
■
Fully Differential Inputs and Outputs
■
Compatible with Popular Differential Amplifier
Using a proprietary internal architecture, the LT6600-2.5
integrates an antialiasing filter and a differential amplifier/
driver without compromising distortion or low noise
performance. At unity gain the measured in band
signal-to-noise ratio is an impressive 86dB. At higher
gains the input referred noise decreases so the part can
Pinouts
SO-8 Package
■
U
APPLICATIO S
■
High Speed ADC Antialiasing and DAC Smoothing in
Networking or Cellular Base Station Applications
High Speed Test and Measurement Equipment
Medical Imaging
Drop-in Replacement for Differential Amplifiers
, LTC and LT are registered trademarks of Linear Technology Corporation.
process smaller input differential signals without signifi-
cantly degrading the output signal-to-noise ratio.
■
■
■
The LT6600-2.5 also features low voltage operation. The
differential design provides outstanding performance for
a4VP-P signallevelwhilethepartoperateswithasingle3V
supply. The LT6600-2.5 is available in an SO-8 package.
For similar devices with higher cutoff frequency, refer to
the LT6600-10 and LT6600-20 data sheets.
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TYPICAL APPLICATIO
Amplitude Response
12
V
= ±2.5V
S
0
–12
–24
–36
–48
–60
–72
–84
–96
5V
0.1µF
1580Ω
3
1
7
2
8
–
+
V
V
–
IN
IN
4
+
–
V
OUT
LT6600-2.5
0.01µF
1580Ω
V
OUT
5
+
6
660025 TA01a
100k
1M
10M
50M
FREQUENCY (Hz)
660025 TA01b
660025i
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
1
LT6600-2.5
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ABSOLUTE AXI U RATI GS
(Note 1)
PACKAGE/ORDER I FOR ATIO
Total Supply Voltage................................................ 11V
Operating Temperature Range (Note 6) ...–40°C to 85°C
Specified Temperature Range (Note 7)....–40°C to 85°C
Junction Temperature........................................... 150°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
TOP VIEW
NUMBER
–
+
IN
1
2
3
4
8
7
6
5
IN
V
V
LT6600CS8-2.5
LT6600IS8-2.5
OCM
MID
–
+
V
V
+
–
OUT
OUT
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
660025
600I25
TJMAX = 150°C, θJA = 100°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 1580Ω, and RLOAD = 1k.
PARAMETER
Filter Gain, V = 3V
CONDITIONS
MIN
– 0.5
– 0.15
– 0.2
– 0.6
–2.1
TYP
0.1
MAX
0.4
0.1
0.6
0.5
0
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
= 2V , f = DC to 260kHz
P-P IN
S
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
R
= 1580Ω
= 2V , f = 700kHz (Gain Relative to 260kHz)
●
●
●
●
●
●
0
IN
P-P IN
= 2V , f = 1.9MHz (Gain Relative to 260kHz)
0.2
P-P IN
= 2V , f = 2.2MHz (Gain Relative to 260kHz)
0.1
P-P IN
= 2V , f = 2.5MHz (Gain Relative to 260kHz)
0.9
P-P IN
= 2V , f = 7.5MHz (Gain Relative to 260kHz)
– 34
– 51
–0.1
0
– 31
P-P IN
= 2V , f = 12.5MHz (Gain Relative to 260kHz)
P-P IN
Filter Gain, V = 5V
= 2V , f = DC to 260kHz
–0.5
– 0.15
– 0.2
– 0.6
– 2.1
0.4
0.1
0.6
0.5
0
S
P-P IN
R
= 1580Ω
= 2V , f = 700kHz (Gain Relative to 260kHz)
●
●
●
●
●
●
IN
P-P IN
= 2V , f = 1.9MHz (Gain Relative to 260kHz)
0.2
P-P IN
= 2V , f = 2.2MHz (Gain Relative to 260kHz)
0.1
P-P IN
= 2V , f = 2.5MHz (Gain Relative to 260kHz)
–0.9
–34
–51
–0.1
P-P IN
= 2V , f = 7.5MHz (Gain Relative to 260kHz)
–31
P-P IN
= 2V , f = 12.5MHz (Gain Relative to 260kHz)
P-P IN
Filter Gain, V = ±5V
= 2V , f = DC to 260kHz
–0.6
0.4
S
P-P IN
Filter Gain, R = 402Ω
V
V
V
= 2V , f = DC to 260kHz, V = 3V
11.3
11.3
11.2
11.8
11.8
11.7
12.3
12.3
12.2
dB
dB
dB
IN
IN
IN
IN
P-P IN
S
= 2V , f = DC to 260kHz, V = 5V
P-P IN
S
= 2V , f = DC to 260kHz, V = ±5V
P-P IN
S
Filter Gain Temperature Coefficient (Note 2)
f
= 260kHz, V = 2V
P-P
780
51
ppm/C
IN
IN
Noise
Noise BW = 10kHz to 2.5MHz
1MHz, 1V , R = 800Ω
µV
RMS
Distortion (Note 4)
2nd Harmonic
3rd Harmonic
95
88
dBc
dBc
RMS
L
Differential Output Swing
Input Bias Current
Measured Between Pins 4 and 5
Average of Pin 1 and Pin 8
V = 5V
S
●
●
8.8
5.1
9.3
5.5
V
V
S
P-P DIFF
P-P DIFF
V = 3V
●
– 35
–15
µA
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2
LT6600-2.5
ELECTRICAL CHARACTERISTICS
The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 1580Ω, and RLOAD = 1k.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Referred Differential Offset
R
IN
= 1580Ω
V = 3V
●
●
●
5
5
5
25
30
35
mV
mV
mV
S
V = 5V
S
V = ±5V
S
R
IN
= 402Ω
V = 3V
●
●
●
3
3
3
13
16
20
mV
mV
mV
S
V = 5V
S
V = ±5V
S
Differential Offset Drift
10
µV/°C
Input Common Mode Voltage (Note 3)
Differential Input = 500mV
IN
,
V = 3V
●
●
●
0.0
0.0
–2.5
1.5
3.0
1.0
V
V
V
P-P
S
R
= 402Ω
V = 5V
S
V = ±5V
S
Output Common Mode Voltage (Note 5)
Differential Input = 2V
Pin 7 at Mid-Supply
,
V = 3V
●
●
●
1.0
1.5
–1.0
1.5
3.0
2.0
V
V
V
P-P
S
V = 5V
S
V = ±5V
S
Output Common Mode Offset
(with Respect to Pin 2)
V = 3V
●
●
●
–25
–30
–55
10
5
–10
45
45
35
mV
mV
mV
S
V = 5V
S
V = ±5V
S
Common Mode Rejection Ratio
63
dB
Voltage at V
(Pin 7)
V = 5V
S
●
●
2.46
4.3
2.51
1.5
2.55
7.7
V
V
MID
S
V = 3V
V
V
Input Resistance
Bias Current
5.7
kΩ
MID
V
= V = V /2
V = 5V
●
●
–15
–10
–3
–3
µA
µA
OCM
OCM
MID
S
S
V = 3V
S
Power Supply Current
V = 3V, V = 5V
26
30
33
36
mA
mA
mA
S
S
V = 3V, V = 5V
●
●
S
S
V = ±5V
28
S
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: This is the temperature coefficient of the internal feedback
Note 5: Output common mode voltage is the average of the voltages at
Pins 4 and 5. The output common mode voltage is equal to the voltage
applied to Pin 2.
resistors assuming a temperature independent external resistor (R ).
Note 3: The input common mode voltage is the average of the voltages
Note 6: Both the LT6600CS8-2.5 and LT6600IS8-2.5 are guaranteed
functional over the operating temperature range of –40°C to 85°C.
IN
applied to the external resistors (R ). Specification guaranteed for
Note 7: The LT6600CS8-2.5 is guaranteed to meet specified performance
from 0°C to 70°C and is designed, characterized and expected to meet
specified performance from –40°C and 85°C, but is not tested or QA
sampled at these temperatures. The LT6600IS8-2.5 is guaranteed to meet
specified performance from –40°C to 85°C.
IN
R
IN
≥ 402Ω.
Note 4: Distortion is measured differentially using a single-ended
stimulus. The input common mode voltage, the voltage at Pin 2, and the
voltage at Pin 7 are equal to one half of the total power supply voltage.
660025i
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LT6600-2.5
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PI FU CTIO S
IN– and IN+ (Pins 1, 8): Input Pins. Signals can be applied
to either or both input pins through identical external
resistors, RIN. The DC gain from differential inputs to the
differential outputs is 1580Ω/RIN.
supply applications, bypass Pin 3 to ground and Pin 6 to
ground with a quality 0.1µF ceramic capacitor.
OUT+ and OUT– (Pins 4, 5): Output Pins. Pins 4 and 5 are
the filter differential outputs. Each pin can drive a 100Ω
and/or 50pF load to AC ground.
V
OCM (Pin 2): Is the DC Common Mode Reference Voltage
for the 2nd Filter Stage. Its value programs the common
mode voltage of the differential output of the filter. Pin 2 is
a high impedance input, which can be driven from an
external voltage reference, or Pin 2 can be tied to Pin 7 on
the PC board. Pin 2 should be bypassed with a 0.01µF
ceramiccapacitorunlessitisconnectedtoagroundplane.
V+ and V– (Pins 3, 6): Power Supply Pins. For a single
3.3V or 5V supply (Pin 6 grounded) a quality 0.1µF
ceramic bypass capacitor is required from the positive
supply pin (Pin 3) to the negative supply pin (Pin 6). The
bypass should be as close as possible to the IC. For dual
V
MID (Pin 7): The VMID pin is internally biased at mid-
supply, see block diagram. For single supply operation,
the VMID pin should be bypassed with a quality 0.01µF
ceramic capacitor to Pin 6. For dual supply operation, Pin
7 can be bypassed or connected to a high quality DC
ground. A ground plane should be used. A poor ground
will increase noise and distortion. Pin 7 sets the output
common mode voltage of the 1st stage of the filter. It has
a 5.5kΩ impedance, and it can be overridden with an
external low impedance voltage source.
660025i
4
LT6600-2.5
W
BLOCK DIAGRA
R
IN
+
+
–
–
V
IN
IN
V
OUT
5
V
MID
8
7
6
+
V
11k
11k
PROPRIETARY
LOWPASS
FILTER STAGE
1580Ω
800Ω
–
V
OP AMP
800Ω
800Ω
+
+
OCM
–
–
V
V
OCM
+
+
–
–
800Ω
1580Ω
1
2
3
4
660025 BD
+
–
–
+
V
V
IN
IN
OCM
V
OUT
R
IN
660025i
5
LT6600-2.5
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APPLICATIO S I FOR ATIO
Interfacing to the LT6600-2.5
output voltage is 1.65V, and the differential output voltage
is 2VP-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.
TheLT6600-2.5requirestwoequalexternalresistors,RIN,
to set the differential gain to 1580Ω/RIN. The inputs to the
+
filter 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
4 and 5 of the LT6600-2.5 are the filter outputs. The
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.
+
–
+
difference between VOUT and VOUT is the differential
–
output voltage. The average of VOUT and VOUT 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
DCcoupled. Thecommonmodeinputvoltageis0.5V, and
the differential input voltage is 2VP-P. The common mode
3.3V
0.1µF
V
V
3
–
1580Ω
3
2
1
0
3
2
1
0
1
7
2
8
–
V
V
4
IN
IN
+
–
+
–
V
V
+
V
OUT
OUT
LT6600-2.5
+
V
0.01µF
1580Ω
IN
V
OUT
–
+
OUT
5
+
6
t
t
–
660025 F01
V
IN
Figure 1
3.3V
3
0.1µF
V
V
0.1µF
0.1µF
1580Ω
1580Ω
1
7
2
3
2
1
0
2
1
–
4
+
+
–
V
V
+
OUT
V
V
OUT
LT6600-2.5
+
V
IN
0.01µF
–
OUT
–
0
t
8
OUT
+
5
V
IN
+
6
–1
660025 F02
Figure 2
5V
0.1µF
V
V
3
402Ω
1
–
+
3
3
V
–
4
IN
+
+
–
V
V
OUT
+
7
OUT
LT6600-2.5
2
1
0
2
1
2
8
V
OUT
0.01µF
402Ω
–
V
500mV (DIFF)
P-P
–
OUT
5
V
IN
+
+
V
V
IN
6
t
t
0
–
+
660025 F03
2V
IN
–
Figure 3
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LT6600-2.5
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APPLICATIO S I FOR ATIO
In Figure 3 the LT6600-2.5 is providing 12dB of gain. The
common mode output voltage is set to 2V.
Figure 5 is a laboratory setup that can be used to charac-
terize the LT6600-2.5 using single-ended instruments
with 50Ω source impedance and 50Ω input impedance.
For a 12dB gain configuration the LT6600-2.5 requires a
402Ωsourceresistanceyetthenetworkanalyzeroutputis
calibrated for a 50Ω load resistance. The 1:1 transformer,
53.6Ω and 388Ω resistors satisfy the two constraints
above. The transformer converts the single-ended source
into a differential stimulus. Similarly, the output of the
LT6600-2.5 will have lower distortion with larger load
resistance yet the analyzer input is typically 50Ω. The 4:1
turns (16:1 impedance) transformer and the two 402Ω
resistors of Figure 5, present the output of the LT6600-2.5
with a 1600Ω differential load, or the equivalent of 800Ω
to ground at each output. The impedance seen by the
network analyzer input is still 50Ω, reducing reflections in
the cabling between the transformer and analyzer input.
Use Figure 4 to determine the interface between the
LT6600-2.5 and a current output DAC. The gain, or “trans-
impedance,” is defined as A = VOUT/IIN. To compute the
transimpedance, use the following equation:
1580 •R1
A =
Ω
( )
R1+R2
(
)
By setting R1 + R2 = 1580Ω, the gain equation reduces to
A = R1(Ω).
The voltage at the pins of the DAC is determined by R1,
R2, the voltage on Pin 7 and the DAC output current.
Consider Figure 4 with R1 = 49.9Ω and R2 = 1540Ω. The
voltage at Pin 7 is 1.65V. The voltage at the DAC pins is
given by:
Differential and Common Mode Voltage Ranges
R1
R1•R2
R1+R2
V
DAC = VPIN7
•
+I •
IN
Therail-to-railoutputstageoftheLT6600-2.5canprocess
large differential signal levels. On a 3V supply, the output
signal can be 5.1VP-P. Similarly, a 5V supply can support
signals as large as 8.8VP-P. To prevent excessive power
dissipation in the internal circuitry, the user must limit
R1+R2 +1580
= 26mV +I • 48.3Ω
IN
IIN is IIN+ or IIN–. The transimpedance in this example is
49.6Ω.
differential signal levels to 9VP-P
.
Evaluating the LT6600-2.5
The two amplifiers inside the LT6600-2.5 have indepen-
dent control of their output common mode voltage (see
the “Block Diagram” section). The following guidelines
will optimize the performance of the filter.
The low impedance levels and high frequency operation of
the LT6600-2.5 require some attention to the matching
networks between the LT6600-2.5 and other devices. The
previous examples assume an ideal (0Ω) source imped-
ance and a large (1kΩ) load resistance. Among practical
examples where impedance must be considered is the
evaluation of the LT6600-2.5 with a network analyzer.
Pin 7 can be allowed to float; Pin 7 must be bypassed to an
ACgroundwitha0.01µFcapacitororsomeinstabilitymay
be observed. Pin 7 can be driven from a low impedance
2.5V
0.1µF
CURRENT
OUTPUT
DAC
3.3V
COILCRAFT
TTWB-16A
4:1
COILCRAFT
TTWB-1010
NETWORK
ANALYZER
SOURCE
NETWORK
ANALYZER
INPUT
0.1µF
3
388Ω
1:1
1
7
2
8
402Ω
–
4
–
+
3
R2
R2
I
I
IN
1
7
2
8
50Ω
LT6600-2.5
–
4
+
–
53.6Ω
50Ω
V
V
+
OUT
R1
+
–
0.01µF
LT6600-2.5
5
+
402Ω
388Ω
–
6
IN
OUT
0.1µF
5
+
660025 F05
6
R1
660025 F04
–2.5V
Figure 5
Figure 4
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LT6600-2.5
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APPLICATIO S I FOR ATIO
source, provided it remains at least 1.5V above V– and at
least 1.5V below V+. An internal resistor divider sets the
voltage of Pin 7. 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 Pin 7.
amplifier inside the LT6600-2.5, and therefore sets the
common mode output voltage of the filter. Since, in the
example of Figure 3, Pin 2 differs from Pin 7 by 0.5V, an
additional 625µA (312µA per side) of DC current will flow
in the resistors coupling the 1st differential amplifier
output stage to filter output. Thus, a total of 3.125mA is
used to translate the common mode voltages.
Pin 2 can be shorted to Pin 7 for simplicity. If a different
common mode output voltage is required, connect Pin 2
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at Pin 2 must be less than or equal to
the mid supply level. For example, voltage (Pin 2) ≤ 1.65V
on a single 3.3V supply. For power supply voltages higher
than 3.3V the voltage at Pin 2 can be set above mid supply.
The voltage on Pin 2 should not exceed 1V below the
voltage on Pin 7. The voltage on Pin 2 should not be more
than 2V above the voltage on Pin 7. Pin 2 is a high
impedance input.
A simple modification to Figure 3 will reduce the DC
common mode currents by 36%. If Pin 7 is shorted to
Pin 2 the common mode output voltage of both op amp
stages will be 2V and the resulting DC current will be 2mA.
Of course, by AC coupling the inputs of Figure 3, the
common mode DC current can be reduced to 625µA.
Noise
The noise performance of the LT6600-2.5 can be evalu-
ated with the circuit of Figure 6.
TheLT6600-2.5wasdesignedtoprocessavarietyofinput
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 VIN and VIN in Figure 1) is determined by
the power supply level and gain setting (see “Electrical
Characteristics”).
Given the low noise output of the LT6600-2.5 and the 6dB
attenuation of the transformer coupling network, it will be
necessary to measure the noise floor of the spectrum
analyzer and subtract the instrument noise from the filter
noise measurement.
+
–
Example: With the IC removed and the 25Ω resistors
grounded, Figure 6, measure the total integrated noise
(eS) of the spectrum analyzer from 10kHz to 2.5MHz. With
the IC inserted, the signal source (VIN) disconnected, and
the input resistors grounded, measure the total integrated
noise out of the filter (eO). With the signal source con-
nected, set the frequency to 100kHz and adjust the ampli-
tude until VIN measures 100mVP-P. Measure the output
amplitude, VOUT, and compute the passband gain
Common Mode DC Currents
In applications like Figure 1 and Figure 3 where the
LT6600-2.5 not only provides lowpass filtering but also
level shifts the common mode voltage of the input signal,
DC currents will be generated through the DC path be-
tweeninputandoutputterminals.Minimizethesecurrents
to decrease power dissipation and distortion.
2.5V
0.1µF
Consider the application in Figure 3. Pin 7 sets the output
common mode voltage of the 1st differential amplifier
inside the LT6600-2.5 (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 1580Ω feedback resis-
tor and the external 402Ω input resistor. The resulting
1.25mA common mode DC current in each input path,
must be absorbed by the sources VIN+ and VIN–. Pin 2 sets
the common mode output voltage of the 2nd differential
SPECTRUM
COILCRAFT
ANALYZER
R
R
3
TTWB-1010
1:1
IN
IN
V
IN
INPUT
1
7
2
8
25Ω
–
4
+
LT6600-2.5
50Ω
–
5
+
25Ω
0.1µF
6
66002 F06
–2.5V
Figure 6
660025i
8
LT6600-2.5
U
W U U
APPLICATIO S I FOR ATIO
50
40
30
20
10
0
100
80
A = VOUT/VIN. Now compute the input referred integrated
noise (eIN) as:
SPECTRAL DENSITY
(eO)2 –(eS)2
60
eIN =
A
40
Table 1 lists the typical input referred integrated noise for
various values of RIN.
20
INTEGRATED
Figure 7 is plot of the noise spectral density as a function
of frequency for an LT6600-2.5 with RIN = 1580Ω using
the fixture of Figure 6 (the instrument noise has been
subtracted from the results).
0
0.01
0.1
1
10
FREQUENCY (MHz)
66002 F07
Figure 7. Input Referred Noise, Gain = 1
Table 1. Noise Performance
INPUT REFERRED
INTEGRATED NOISE INTEGRATED NOISE
10kHz TO 2.5MHz 10kHz TO 5MHz
INPUT REFERRED
Table 2. LT6600-2.5 SO-8 Package Thermal Resistance
COPPER AREA
PASSBAND
GAIN (V/V)
R
IN
TOPSIDE BACKSIDE BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
4
2
1
402Ω
806Ω
18µV
29µV
51µV
23µV
39µV
73µV
RMS
RMS
RMS
RMS
RMS
RMS
2
2
2
(mm )
(mm )
(mm )
1100
330
35
1100
330
35
2500
2500
2500
2500
2500
65°C/W
1580Ω
85°C/W
95°C/W
The noise at each output is comprised of a differential
component and a common mode component. Using a
transformerorcombinertoconvertthedifferentialoutputs
tosingle-endedsignalrejectsthecommonmodenoiseand
gives a true measure of the S/N achievable in the system.
Conversely,ifeachoutputismeasuredindividuallyandthe
noisepoweraddedtogether,theresultingcalculatednoise
level will be higher than the true differential noise.
35
0
100°C/W
0
0
105°C/W
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.
Junction temperature, TJ, is calculated from the ambient
temperature, TA, and power dissipation, PD. The power
dissipation is the product of supply voltage, VS, and
supply current, IS. Therefore, the junction temperature is
given by:
Power Dissipation
TheLT6600-2.5amplifierscombinehighspeedwithlarge-
signal currents in a small package. There is a need to
ensure that the dies’s junction temperature does not
exceed150°C. TheLT6600-2.5packagehasPin6fusedto
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
copper, a total of 660 square millimeters connected to Pin
6 of the LT6600-2.5 (330 square millimeters on each side
of the PC board) will result in a thermal resistance, θJA, of
TJ = TA + (PD • θJA) = TA + (VS • IS • θJA)
where the supply current, IS, is a function of signal level,
load impedance, temperature and common mode
voltages.
For a given supply voltage, the worst-case power dissi-
pation occurs when the differential input signal is maxi-
mum, the common mode currents are maximum (see
Applications Information regarding Common Mode DC
660025i
9
LT6600-2.5
U
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APPLICATIO S I FOR ATIO
Currents), the load impedance is small and the ambient
temperature is maximum. To compute the junction tem-
perature, measure the supply current under these worst-
case conditions, estimate the thermal resistance from
Table2, thenapplytheequationforTJ. Forexample, using
the circuit in Figure 3 with DC differential input voltage of
1V, a differential output voltage of 4V, no load resistance
and an ambient temperature of 85°C, the supply current
(current into Pin 3) measures 37.6mA. Assuming a PC
board layout with a 35mm2 copper trace, the θJA is
100°C/W. The resulting junction temperature is:
TJ = TA + (PD • θJA) = 85 + (5 • 0.0376 • 100) = 104°C
When using higher supply voltages or when driving small
impedances, more copper may be necessary to keep TJ
below 150°C.
660025i
10
LT6600-2.5
U
PACKAGE DESCRIPTIO
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
.045 ±.005
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
3
4
2
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
INCHES
1. DIMENSIONS IN
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0303
660025i
11
LT6600-2.5
RELATED PARTS
PART NUMBER
LTC®1565-31
LTC1566-1
LT1567
DESCRIPTION
COMMENTS
650kHz Linear Phase Lowpass Filter
Continuous Time, SO8 Package, Fully Differential
Continuous Time, SO8 Package
Low Noise, 2.3MHz Lowpass Filter
Very Low Noise, High Frequency Filter Building Block
Very Low Noise, 4th Order Building Block
1.4nV/√Hz Op Amp, MSOP Package, Fully Differential
LT1568
Lowpass and Bandpass Filter Designs Up to 10MHz,
Differential Outputs
LT6600-10
LT6600-20
Very Low Noise Differential Amplifier and 10MHz
Lowpass Filter
82dB S/N with 3V Supply, SO-8 Package
Very Low Noise Differential Amplifier and 20MHz
Lowpass Filter
76dB S/N with 3V Supply, SO-8 Package
660025i
LT/TP 0603 1K • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2003
相关型号:
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