LT6600-2.5
Very Low Noise, Differential
Amplifier and 2.5MHz Lowpass Filter
FEATURES
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DESCRIPTION
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 ampli-
fiers require many precision external components to tail
or gain and bandwidth. In contrast, with the LT6600-2.5,
two external resistors program differential gain, and the
filter’s 2.5MHz cutoff frequency and passband ripple are
internally set. The LT6600-2.5 also provides the necessary
level shifting to set its output common mode voltage to ac-
commodate the reference voltage requirements of A/Ds.
Using a proprietary internal architecture, the LT6600-2.5
integrates an antialiasing filter and a differential ampli-
fier/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 process
smaller input differential signals without significantly
degrading the output signal-to-noise ratio.
The LT6600-2.5 also features low voltage operation. The
differential design provides outstanding performance for a
4V
P-P
signal level while the part operates with a single 3V
supply. The LT6600-2.5 is available in SO-8 and DFN-12
packages.
For similar devices with higher cutoff frequency, refer
to the LT6600-5, LT6600-10, LT6600-15 and LT6600-20
data sheets.
±0.6dB (Max) Ripple 4th Order Lowpass Filter with
2.5MHz Cutoff
Programmable Differential Gain via Two External
Resistors
Adjustable Output Common Mode Voltage
Operates and Specified with 3V, 5V, ±5V Supplies
86dB S/N with 3V Supply and 1V
RMS
Output
Low Distortion, 1V
RMS
, 800Ω Load
1MHz: 95dBc 2nd, 88dBc 3rd
Fully Differential Inputs and Outputs
Compatible with Popular Differential Amplifier
Pinouts
SO-8 and DFN-12 Packages
APPLICATIONS
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High Speed ADC Antialiasing and DAC Smoothing in
Networking or Cellular Basestation Applications
High Speed Test and Measurement Equipment
Medical Imaging
Drop-in Replacement for Differential Amplifiers
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
DAC Output Filter
5V
52.3Ω
16-BIT 4kHz to 2.5MHz
DISCRETE MULTI-TONE
SIGNAL AT 50MSPS
LADCOM
I
OUT A
LTC1668
I
OUT B
CLK
–5V 50MHz
52.3Ω
(S8 Pin Numbers Shown)
DAC Output Spectrum
0
5V
0.1μF
–10
–20
BASEBAND SIGNAL
–10
–20
–30
(dBm)
–40
–50
–60
–70
–80
–90
0
12 24 36 48 60 72 84 96 108 120
FREQUENCY (MHz)
660025 TA01b
LT6600-2.5 Output Spectrum
0
1580Ω
1
7
2
8
–
3
(dBm)
LT6600-2.5
+
4
–30
V
OUT+
V
OUT–
–40
–50
–60
–70
–80
DAC OUTPUT IMAGE
+
–
6
5
1580Ω
0.1μF
–5V
660025 TA01a
–90
0
12 24 36 48 60 72 84 96 108 120
FREQUENCY (MHz)
660025 TA01c
660025fe
1
LT6600-2.5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Total Supply Voltage .................................................11V
Input Current (Note 8)..........................................±10mA
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
PIN CONFIGURATION
TOP VIEW
IN
–
NC
V
OCM
V
+
NC
OUT
+
1
2
3
4
5
6
12
12 IN
+
11 NC
10 V
MID
9 V
–
8 V
–
7 OUT
–
IN
–
1
V
OCM
2
V
+
3
OUT
+
4
TOP VIEW
8
7
6
5
IN
+
V
MID
V
–
OUT
–
DF PACKAGE
12-LEAD (4mm
×
4mm) PLASTIC DFN
T
JMAX
= 150°C,
θ
JA
= 43°C/W,
θ
JC
= 4°C/W
EXPOSED PAD (PIN 13) IS V
–
, MUST BE SOLDERED TO PCB
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 100°C/W
ORDER INFORMATION
LEAD FREE FINISH
LT6600CS8-2.5#PBF
LT6600IS8-2.5#PBF
LT6600CDF-2.5#PBF
LT6600IDF-2.5#PBF
LEAD BASED FINISH
LT6600CS8-2.5
LT6600IS8-2.5
TAPE AND REEL
LT6600CS8-2.5#TRPBF
LT6600IS8-2.5#TRPBF
LT6600CDF-2.5#TRPBF
LT6600IDF-2.5#TRPBF
TAPE AND REEL
LT6600CS8-2.5#TR
LT6600IS8-2.5#TR
PART MARKING*
660025
600I25
60025
60025
PART MARKING
660025
600I25
PACKAGE DESCRIPTION
8-Lead Plastic SO
8-Lead Plastic SO
12-Lead (4mm
×
4mm) Plastic DFN
12-Lead (4mm
×
4mm) Plastic DFN
PACKAGE DESCRIPTION
8-Lead Plastic SO
8-Lead Plastic SO
SPECIFIED TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
SPECIFIED TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
*The temperature grade is identified by a label on the shipping container for the DFN Package.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. Unless otherwise specified V
S
= 5V (V
+
= 5V, V
–
= 0V), R
IN
= 1580Ω, and R
LOAD
= 1k.
PARAMETER
Filter Gain, V
S
= 3V
R
IN
= 1580Ω
CONDITIONS
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 2V
P-P
, f
IN
= 700kHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 1.9MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 2.2MHz (Gain Relative to 260kHz)
l
l
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ELECTRICAL CHARACTERISTICS
MIN
–0.5
–0.15
–0.2
–0.6
TYP
0.1
0
0.2
0.1
MAX
0.4
0.1
0.6
0.5
UNITS
dB
dB
dB
dB
660025fe
2
LT6600-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
V
IN
= 2V
P-P
, f
IN
= 2.5MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 7.5MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 12.5MHz (Gain Relative to 260kHz)
Filter Gain, V
S
= 5V
R
IN
= 1580Ω
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 2V
P-P
, f
IN
= 700kHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 2.2MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 2.2MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 2.5MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 7.5MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 12.5MHz (Gain Relative to 260kHz)
Filter Gain, V
S
= ±5V
Filter Gain, R
IN
= 402Ω
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 0.5V
P-P
, f
IN
= DC to 260kHz, V
S
= 3V
V
IN
= 0.5V
P-P
, f
IN
= DC to 260kHz, V
S
= 5V
V
IN
= 0.5V
P-P
, f
IN
= DC to 260kHz, V
S
= ±5V
Noise BW = 10kHz to 2.5MHz
1MHz, 1V
RMS
, R
L
= 800Ω
Measured Between Pins 4 and 5
Average of Pin 1 and Pin 8
R
IN
= 1580Ω, Differential Gain = 1V/V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 5V (S8)
V
S
= 5V (DFN)
V
S
= 3V
V
OCM
= V
MID
= V
S
/2
V
S
= 5V
V
S
= 3V
V
S
= 3V, V
S
= 5V
V
S
= 3V, V
S
= 5V
V
S
= ±5V
2nd Harmonic
3rd Harmonic
V
S
= 5V
V
S
= 3V
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The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. Unless otherwise specified V
S
= 5V (V
+
= 5V, V
–
= 0V), R
IN
= 1580Ω, and R
LOAD
= 1k.
MIN
–2.1
TYP
–0.9
–34
–51
–0.5
–0.15
–0.2
–0.6
–2.1
–0.1
0
0.2
0.1
–0.9
–34
–51
–0.6
11.3
11.3
11.2
–0.1
11.8
11.8
11.7
780
51
95
88
8.8
5.1
–35
9.3
5.5
–15
5
5
5
3
3
3
10
Differential Input = 500mV
P-P
,
R
IN
≥ 402Ω
Differential Input = 2V
P-P
,
Pin 7 = Open
0.0
0.0
–2.5
1.0
1.5
–1.0
–25
–30
–55
2.46
2.45
4.3
–15
–10
10
5
–10
63
2.51
2.51
1.5
5.7
–3
–3
26
28
30
33
36
2.55
2.56
7.7
1.5
3.0
1.0
1.5
3.0
2.0
45
45
35
25
30
35
13
16
20
0.4
12.3
12.3
12.2
0.4
0.1
0.6
0.5
0
–31
MAX
0
–31
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
ppm/°C
μV
RMS
dBc
dBc
V
P-P DIFF
V
P-P DIFF
μA
mV
mV
mV
mV
mV
mV
μV/°C
V
V
V
V
V
V
mV
mV
mV
dB
V
V
V
kΩ
μA
μA
mA
mA
mA
660025fe
Filter Gain Temperature Coefficient (Note 2) f
IN
= 260kHz, V
IN
= 2V
P-P
Noise
Distortion (Note 4)
Differential Output Swing
Input Bias Current
Input Referred Differential Offset
R
IN
= 402Ω, Differential Gain = 4V/V
Differential Offset Drift
Input Common Mode Voltage (Note 3)
Output Common Mode Voltage (Note 5)
Output Common Mode Offset
(with Respect to Pin 2)
Common Mode Rejection Ratio
Voltage at V
MID
(Pin 7)
V
MID
Input Resistance
V
OCM
Bias Current
Power Supply Current
3
LT6600-2.5
ELECTRICAL CHARACTERISTICS
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
This is the temperature coefficient of the internal feedback
resistors assuming a temperature independent external resistor (R
IN
).
Note 3:
The input common mode voltage is the average of the voltages
applied to the external resistors (R
IN
). Specification guaranteed for R
IN
≥ 402Ω. For ±5V supplies, the minimum input common mode voltage is
guaranteed by design to reach –5V.
Note 4:
Distortion is measured differentially using a single-ended stimulus.
The input common mode voltage, the voltage at V
OCM
, and the voltage at
V
MID
are equal to one half of the total power supply voltage.
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.
Note 6:
The LT6600C-2.5 is guaranteed functional over the operating
temperature range of –40°C to 85°C.
Note 7:
The LT6600C-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 LT6600I-2.5 is guaranteed to meet
specified performance from –40°C to 85°C.
Note 8:
The inputs are protected by back-to-back diodes. If the differential
input voltage exceeds 1.4V, the input current should be limited to less than
10mA.
TYPICAL PERFORMANCE CHARACTERISTICS
Amplitude Response
12
0
–12
–24
GAIN (dB)
–36
–48
–60
–72
–84
–96
100k
1M
10M
FREQUENCY (Hz)
50M
660025 G01
Passband Gain and Group Delay
V
S
= ±2.5V
R
IN
= 1580Ω
GAIN = 1
1
0
–1
–2
GAIN (dB)
–3
–4
–5
–6
320
300
280
260
240
220
200
GROUP DELAY (ns)
12
11
10
9
GAIN (dB)
8
7
6
5
Passband Gain and Group Delay
320
300
280
260
240
220
200
GROUP DELAY (ns)
180
V
S
= 5V
–7
R
IN
= 1580Ω 160
GAIN = 1
–8
140
T
A
= 25°C
–9
120
0.5
0.75
1.0
1.25
1.5
1.75
2.0
2.25
2.5
2.75
3.0
FREQUENCY (MHz)
660025 G02
180
V
S
= 5V
4
R
IN
= 402Ω 160
GAIN = 4
140
3
T
A
= 25°C
120
2
0.5
0.75
1.0
1.25
1.5
1.75
2.0
2.25
2.5
2.75
3.0
FREQUENCY (MHz)
660025 G03
Output Impedance
vs Frequency (OUT
+
or OUT
–
)
100
110
CMRR
V
IN
= 1V
P-P
V
S
= 5V
100 R = 1580Ω
IN
GAIN = 1
90
CMRR (dB)
80
70
60
20
50
10
0
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
660025 G05
PSRR
90
80
70
60
PSRR (dB)
50
40
30
V
+
TO
DIFFERENTIAL OUT
V
S
= 3V
OUTPUT IMPEDANCE (Ω)
10
1
0.1
100k
1M
10M
FREQUENCY (Hz)
100M
660025 G04
40
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
660025 G06
660025fe
4
LT6600-2.5
TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Frequency
–60
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–60
Distortion vs Frequency
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–70
DISTORTION (dB)
–70
DISTORTION (dB)
–80
–80
–90
V
IN
= 2V
P-P
V
S
= 3V
R
L
= 800Ω AT
EACH OUTPUT
0.1
1
FREQUENCY (MHz)
10
660025 G07
–90
V
IN
= 2V
P-P
V
S
= 5V
R
L
= 800Ω AT
EACH OUTPUT
0.1
1
FREQUENCY (MHz)
10
660025 G08
–100
–100
–110
–110
Distortion vs Frequency
–60
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–40
–50
–60
–70
–80
–90
–100
V
IN
= 2V
P-P
V
S
= ±5V
R
L
= 800Ω AT
EACH OUTPUT
0.1
1
FREQUENCY (MHz)
10
660025 G09
Distortion vs Signal Level
2ND HARMONIC,
DIFFERENTIAL INPUT
3RD HARMONIC,
DIFFERENTIAL INPUT
2ND HARMONIC,
SINGLE-ENDED INPUT
3RD HARMONIC,
SINGLE-ENDED INPUT
–70
DISTORTION (dB)
–80
–90
DISTORTION (dB)
–100
–110
0
1
–110
V
S
= 3V
F = 1MHz
R
L
= 800Ω AT
EACH OUTPUT
2
3
4
INPUT LEVEL (V
P-P
)
5
6
660025 G10
Distortion vs Signal Level
–40
–50
–60
–70
–80
–90
–100
–110
0
1
2
V
S
= 5V
F = 1MHz
R
L
= 800Ω AT
EACH OUTPUT
3
4
5
6
7
INPUT LEVEL (V
P-P
)
8
9
2ND HARMONIC,
DIFFERENTIAL INPUT
3RD HARMONIC,
DIFFERENTIAL INPUT
2ND HARMONIC,
SINGLE-ENDED INPUT
3RD HARMONIC,
SINGLE-ENDED INPUT
–40
–50
–60
–70
–80
–90
–100
–110
Distortion vs Signal Level
2ND HARMONIC,
DIFFERENTIAL INPUT
3RD HARMONIC,
DIFFERENTIAL INPUT
2ND HARMONIC,
SINGLE-ENDED INPUT
3RD HARMONIC,
SINGLE-ENDED INPUT
DISTORTION (dB)
DISTORTION (dB)
V
S
= ±5V
F = 1MHz
R
L
= 800Ω AT
EACH OUTPUT
0
1
2
3
4
5
6
7
INPUT LEVEL (V
P-P
)
8
9
660025 G11
660025 G12
660025fe
5
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