Final Electrical Specifications
LT6600-2.5
Very Low Noise, Differential
Amplifier and 2.5MHz Lowpass Filter
June 2003
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
s
s
Programmable Differential Gain via Two External
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 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 Package
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
external resistors program differential gain, and the filter’s
2.5MHz cutoff frequency and passband ripple are inter-
nally set. The LT6600-2.5 also provides the necessary level
shifting to set its output common mode voltage to accom-
modate the reference voltage requirements of A/Ds.
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
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
a 4V
P-P
signal level while the part operates with a single 3V
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.
APPLICATIO S
s
s
s
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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.
TYPICAL APPLICATIO
5V
12
0
0.1µF
1580Ω
–12
–24
7
0.01µF
V
IN+
1580Ω
8
–
GAIN (dB)
V
IN–
1
3
4
V
OUT+
V
OUT–
–36
–48
–60
–72
2 LT6600-2.5
+
6
5
660025 TA01a
–84
–96
100k
1M
10M
FREQUENCY (Hz)
50M
660025 TA01b
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
Amplitude Response
V
S
=
±2.5V
U
U
660025i
1
LT6600-2.5
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
IN
–
1
V
OCM
2
V
+
3
OUT
+
4
8
7
6
5
IN
+
V
MID
V
–
OUT
–
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
NUMBER
LT6600CS8-2.5
LT6600IS8-2.5
S8 PART MARKING
660025
600I25
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 100°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications that 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)
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)
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)
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)
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz, V
S
= 3V
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz, V
S
= 5V
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz, V
S
=
±5V
f
IN
= 260kHz, V
IN
= 2V
P-P
Noise BW = 10kHz to 2.5MHz
1MHz, 1V
RMS
, R
L
= 800Ω
2nd Harmonic
3rd Harmonic
Measured Between Pins 4 and 5
V
S
= 5V
V
S
= 3V
Average of Pin 1 and Pin 8
MIN
– 0.5
– 0.15
– 0.2
– 0.6
– 2.1
TYP
0.1
0
0.2
0.1
0.9
– 34
– 51
–0.1
0
0.2
0.1
–0.9
– 34
– 51
– 0.1
11.8
11.8
11.7
780
51
95
88
9.3
5.5
– 15
MAX
0.4
0.1
0.6
0.5
0
– 31
0.4
0.1
0.6
0.5
0
–31
0.4
12.3
12.3
12.2
UNITS
dB
dB
dB
dB
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
ELECTRICAL CHARACTERISTICS
q
q
q
q
q
q
q
q
q
q
q
q
Filter Gain, V
S
= 5V
R
IN
= 1580Ω
– 0.5
– 0.15
– 0.2
– 0.6
– 2.1
Filter Gain, V
S
=
±5V
Filter Gain, R
IN
= 402Ω
– 0.6
11.3
11.3
11.2
Filter Gain Temperature Coefficient (Note 2)
Noise
Distortion (Note 4)
Differential Output Swing
Input Bias Current
q
q
q
8.8
5.1
– 35
660025i
2
U
W
U
U
W W
W
LT6600-2.5
The
q
denotes specifications that 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
Input Referred Differential Offset
CONDITIONS
R
IN
= 1580Ω
MIN
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
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
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
R
IN
= 402Ω
Differential Offset Drift
Input Common Mode Voltage (Note 3)
TYP
5
5
5
3
3
3
10
MAX
25
30
35
13
16
20
1.5
3.0
1.0
1.5
3.0
2.0
45
45
35
2.55
7.7
Differential Input = 500mV
P-P
,
R
IN
= 402Ω
Differential Input = 2V
P-P
,
Pin 7 at Mid-Supply
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
0.0
0.0
–2.5
1.0
1.5
–1.0
–25
–30
–55
2.46
4.3
–15
–10
10
5
–10
63
2.51
1.5
5.7
–3
–3
26
28
30
33
36
UNITS
mV
mV
mV
mV
mV
mV
µV/°C
V
V
V
V
V
V
mV
mV
mV
dB
V
V
kΩ
µA
µA
mA
mA
mA
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
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.
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.
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:
Both the LT6600CS8-2.5 and LT6600IS8-2.5 are guaranteed
functional over the operating temperature range of –40°C to 85°C.
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.
660025i
3
LT6600-2.5
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, R
IN
. The DC gain from differential inputs to the
differential outputs is 1580Ω/R
IN
.
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
ceramic capacitor unless it is connected to a ground plane.
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
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
MID
(Pin 7):
The V
MID
pin is internally biased at mid-
supply, see block diagram. For single supply operation,
the V
MID
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.
4
U
U
U
660025i
LT6600-2.5
BLOCK DIAGRA
V
IN
+
V
IN–
W
R
IN
8
IN
+
V
MID
7
V
+
11k
1580Ω
11k
800Ω
V
–
OP AMP
V
–
6
OUT
–
5
PROPRIETARY
LOWPASS
FILTER STAGE
+
V
OCM
800Ω
–
+
800Ω
+ –
V
OCM
–
– +
800Ω
1580Ω
1
R
IN
IN
–
2
V
OCM
3
V
+
4
660025 BD
OUT
+
660025i
5
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