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LT6600CS8-5#PBF [Linear]

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LT6600CS8-5#PBF
型号： LT6600CS8-5#PBF
厂家： Linear    Linear
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LT6600-5  
Very Low Noise, Differential  
Amplifier and 5MHz Lowpass Filter  
FEATURES  
DESCRIPTION  
TheLT®6600-5combinesafullydifferentialamplifierwitha  
4thorder5MHzlowpassfilterapproximatinga Chebyshev  
frequency response. Most differential amplifiers require  
many precision external components to tailor gain and  
bandwidth. In contrast, with the LT6600-5, two external  
resistors program differential gain, and the filter’s 5MHz  
cutoff frequency and passband ripple are internally set.  
The LT6600-5 also provides the necessary level shifting  
to set its output common mode voltage to accommodate  
the reference voltage requirements of A/Ds.  
n
Programmable Differential Gain via Two External  
Resistors  
n
Adjustable Output Common Mode Voltage  
Operates and Specified with 3V, 5V, 5V Supplies  
0.5dB Ripple 4th Order Lowpass Filter with 5MHz  
n
n
Cutoff  
n
82dB S/N with 3V Supply and 2V Output  
Low Distortion, 2V , 800Ω Load  
P-P  
n
P-P  
1MHz: 93dBc 2nd, 96dBc 3rd  
Fully Differential Inputs and Outputs  
Compatible with Popular Differential Amplifier  
Pinouts  
n
n
Using a proprietary internal architecture, the LT6600-5  
integrates an antialiasing filter and a differential ampli-  
fier/driver without compromising distortion or low noise  
performance. At unity gain the measured in band sig-  
nal-to-noise ratio is an impressive 82dB. 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.  
n
Available in an SO-8 Package  
APPLICATIONS  
n
High Speed ADC Antialiasing and DAC Smoothing in  
Networking or Cellular Base Station Applications  
n
High Speed Test and Measurement Equipment  
Medical Imaging  
Drop-in Replacement for Differential Amplifiers  
The LT6600-5 also features low voltage operation. The  
differential design provides outstanding performance for  
n
n
a 2V signal level while the part operates with a single  
P-P  
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.  
All other trademarks are the property of their respective owners.  
3V supply.  
For similar devices with other cutoff frequencies, refer to  
the LT6600-20, LT6600-10 and LT6600-2.5.  
TYPICAL APPLICATION  
Dual, Matched, 5MHz Lowpass Filter  
5MHz Phase Distribution  
(50 Units)  
3V  
0.1μF  
30  
25  
20  
15  
10  
5
R
IN  
3
1
4
–
+
0.01μF  
7
2
8
I
IN  
LT6600-5  
Q
OUT  
–
6
+
5
R
IN  
806ꢀ  
GAIN =  
R
V
IN  
OCM  
(1V-1.5V)  
3V 0.1μF  
R
3
4
IN  
1
–
+
LT6600-5  
–
0.01μF  
7
2
8
Q
I
IN  
OUT  
0
–135 –134.5–134–133.5–133–132.5–132–131.5  
+
5
5MHz PHASE (DEG)  
R
6
IN  
66005 TA01  
66005fa  
1
LT6600-5  
ABSOLUTE MAXIMUM RATINGS  
PIN CONFIGURATION  
(Note 1)  
TOP VIEW  
Total Supply Voltage .................................................11V  
–
+
Input Voltage (Note 8)............................................... V  
IN  
1
2
3
4
8
7
6
5
IN  
S
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  
V
V
V
OCM  
MID  
–
+
V
+
–
OUT  
OUT  
S8 PACKAGE  
8-LEAD PLASTIC SO  
T
= 150°C, θ = 100°C/W  
JMAX  
JA  
ORDER INFORMATION  
LEAD FREE FINISH  
LT6600CS8-5#PBF  
LT6600IS8-5#PBF  
LEAD BASED FINISH  
LT6600CS8-5  
TAPE AND REEL  
PART MARKING  
66005  
PACKAGE DESCRIPTION  
8-Lead Plastic SO  
SPECIFIED TEMPERATURE RANGE  
–40°C to 85°C  
LT6600CS8-5#TRPBF  
LT6600IS8-5#TRPBF  
TAPE AND REEL  
6600I5  
8-Lead Plastic SO  
–40°C to 85°C  
PART MARKING  
66005  
PACKAGE DESCRIPTION  
8-Lead Plastic SO  
SPECIFIED TEMPERATURE RANGE  
–40°C to 85°C  
LT6600CS8-5#TR  
LT6600IS8-5#TR  
LT6600IS8-5  
6600I5  
8-Lead Plastic SO  
–40°C to 85°C  
Consult LTC Marketing for parts specified with wider operating temperature ranges.  
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/  
ELECTRICAL CHARACTERISTICS  
The l denotes the specifications which apply over the full operating temperature  
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k.  
PARAMETER  
Filter Gain, V = 3V  
CONDITIONS  
= 2V , f = DC to 260kHz  
MIN  
– 0.5  
–0.15  
–0.4  
– 0.7  
–1.1  
TYP  
0
MAX  
0.5  
UNITS  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
dB  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
V
IN  
S
P-P IN  
l
l
l
l
l
l
= 2V , f = 500k (Gain Relative to 260kHz)  
0
0.1  
P-P IN  
= 2V , f = 2.5MHz (Gain Relative to 260kHz)  
– 0.1  
– 0.1  
–0.2  
– 28  
–44  
0
0.3  
P-P IN  
= 2V , f = 4MHz (Gain Relative to 260kHz)  
0.6  
P-P IN  
= 2V , f = 5MHz (Gain Relative to 260kHz)  
0.8  
P-P IN  
= 2V , f = 15MHz (Gain Relative to 260kHz)  
–25  
P-P IN  
= 2V , f = 25MHz (Gain Relative to 260kHz)  
P-P IN  
Filter Gain, V = 5V  
= 2V , f = DC to 260kHz  
–0.5  
– 0.15  
–0.4  
0.5  
0.1  
0.3  
0.6  
0.8  
–25  
S
P-P IN  
l
l
l
l
l
l
= 2V , f = 500k (Gain Relative to 260kHz)  
0
P-P IN  
= 2V , f = 2.5MHz (Gain Relative to 260kHz)  
–0.1  
–0.1  
–0.2  
–28  
–44  
–0.1  
P-P IN  
= 2V , f = 4MHz (Gain Relative to 260kHz)  
– 0.7  
– 1.1  
P-P IN  
= 2V , f = 5MHz (Gain Relative to 260kHz)  
P-P IN  
= 2V , f = 15MHz (Gain Relative to 260kHz)  
P-P IN  
= 2V , f = 25MHz (Gain Relative to 260kHz)  
P-P IN  
Filter Gain, V = 5V  
= 2V , f = DC to 260kHz  
–0.6  
0.4  
S
P-P IN  
66005fa  
2
LT6600-5  
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature  
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k.  
PARAMETER  
CONDITIONS  
= 2V , f = DC to 260kHz  
MIN  
TYP  
MAX  
UNITS  
Filter Gain, R = 229Ω  
V
V = 3V  
10.4  
10.3  
10.1  
10.9  
10.8  
10.7  
11.5  
11.4  
11.3  
dB  
dB  
dB  
IN  
IN  
P-P IN  
S
V = 5V  
S
V = 5V  
S
Filter Gain Temperature Coefficient (Note 2)  
f
= 260kHz, V = 2V  
P-P  
780  
45  
ppm/C  
IN  
IN  
Noise  
Noise BW = 10kHz to 5MHz, R = 806Ω  
μV  
RMS  
IN  
Distortion (Note 4)  
1MHz, 2V , R = 800Ω  
2nd Harmonic  
3rd Harmonic  
93  
96  
dBc  
dBc  
P-P  
L
5MHz, 2V , R = 800Ω  
2nd Harmonic  
3rd Harmonic  
66  
73  
dBc  
dBc  
P-P  
L
l
l
Differential Output Swing  
Measured Between Pins 4 and 5  
Pin 7 Shorted to Pin 2  
V = 5V  
S
3.85  
3.85  
4.8  
4.8  
V
V
S
P-P DIFF  
P-P DIFF  
V = 3V  
l
Input Bias Current  
Average of Pin 1 and Pin 8  
–70  
–30  
μA  
l
l
l
Input Referred Differential Offset  
R
IN  
= 806Ω  
V = 3V  
5
10  
8
25  
30  
35  
mV  
mV  
mV  
S
V = 5V  
S
V = 5V  
S
l
l
l
R
= 229Ω  
V = 3V  
5
5
5
13  
16  
20  
mV  
mV  
mV  
IN  
S
V = 5V  
S
V = 5V  
S
Differential Offset Drift  
10  
μV/°C  
l
l
l
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
= 229Ω  
V = 5V  
S
V = 5V  
S
l
l
l
Output Common Mode Voltage (Note 5)  
Differential Output = 2V  
Pin 7 at Midsupply  
,
V = 3V  
1.0  
1.5  
–2.5  
1.5  
3.0  
2.0  
V
V
V
P-P  
S
V = 5V  
S
V = 5V  
S
l
l
l
Output Common Mode Offset  
(with Respect to Pin 2)  
V = 3V  
–25  
–30  
–55  
5
0
–5  
50  
45  
35  
mV  
mV  
mV  
S
V = 5V  
S
V = 5V  
S
Common Mode Rejection Ratio  
61  
dB  
l
l
Voltage at V  
(Pin 7)  
V = 5  
S
2.46  
4.3  
2.51  
1.5  
2.55  
7.7  
V
V
MID  
S
V = 3  
V
V
Input Resistance  
Bias Current  
5.5  
kꢀ  
MID  
l
l
V
OCM  
= V  
= V /2  
V = 5  
–15  
–10  
–3  
–3  
μA  
μA  
OCM  
MID  
S
S
V = 3  
S
Power Supply Current  
V = 3V, V = 5  
28  
31  
34  
38  
mA  
mA  
mA  
S
S
l
l
V = 3V, V = 5  
S
S
V = 5V  
30  
S
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 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 is guaranteed functional over the operating  
Note 2: This is the temperature coefficient of the internal feedback  
temperature range –40°C to 85°C.  
resistors assuming a temperature independent external resistor (R ).  
Note 3: The input common mode voltage is the average of the voltages  
IN  
Note 7: The LT6600C is guaranteed to meet 0°C to 70°C specifications and  
is designed, characterized and expected to meet the extended temperature  
limits, but is not tested at –40°C and 85°C. The LT6600I is guaranteed to  
meet specified performance from –40°C to 85°C.  
applied to the external resistors (R ). Specification guaranteed for  
IN  
R
≥ 229ꢀ.  
IN  
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.  
Note 4: Distortion is measured differentially using a differential 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.  
66005fa  
3
LT6600-5  
TYPICAL PERFORMANCE CHARACTERISTICS  
Amplitude Response  
Passband Gain and Delay  
Passband Gain and Delay  
1
0
13  
12  
11  
10  
9
120  
110  
100  
90  
120  
110  
100  
90  
10  
0
V
= 5V  
GAIN  
S
GAIN  
GAIN = 1  
= 25°C  
T
A
–1  
–2  
–3  
–4  
–5  
–6  
–7  
–8  
–9  
–10  
–20  
–30  
–40  
–50  
–60  
–70  
–80  
80  
80  
DELAY  
DELAY  
70  
70  
8
60  
60  
7
50  
50  
6
40  
40  
5
GAIN = 1  
GAIN = 4  
30  
30  
4
T
= 25°C  
T = 25°C  
A
A
20  
10  
3
20  
0
1
2
3
4
5
6
7
8
9
0
1
2
3
7
4
5
6
8
9
10  
0.1  
1
10  
100  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
66005 G01  
66005 G02  
66005 G03  
Output Impedance vs Frequency  
Common Mode Rejection Ratio  
Power Supply Rejection Ratio  
100  
10  
1
90  
80  
70  
60  
50  
40  
30  
80  
70  
60  
50  
40  
30  
20  
10  
0
V
= 5V  
V
= 5V  
S
S
GAIN = 1  
= 25°C  
GAIN = 1  
= 1V  
T
V
A
A
IN  
P-P  
T
= 25°C  
V
V
= 3V  
S
= 200mV  
= 25°C  
IN  
P-P  
T
A
+
V
TO DIFFOUT  
0.1  
0.1  
1
10  
100  
0.01  
0.1  
1
10  
100  
0.01  
0.1  
1
10  
100  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
FREQUENCY (MHz)  
66005 G04  
66005 G05  
66005 G06  
Distortion vs Frequency  
Distortion vs Frequency  
Distortion vs Signal Level  
–50  
–60  
–50  
–40  
–50  
DIFFERENTIAL INPUT,  
2ND HARMONIC  
DIFFERENTIAL INPUT,  
3RD HARMONIC  
SINGLE-ENDED INPUT,  
2ND HARMONIC  
SINGLE-ENDED INPUT,  
3RD HARMONIC  
DIFFERENTIAL INPUT,  
2ND HARMONIC  
DIFFERENTIAL INPUT,  
3RD HARMONIC  
SINGLE-ENDED INPUT,  
2ND HARMONIC  
SINGLE-ENDED INPUT,  
3RD HARMONIC  
V
= 3V  
= 800ꢀ  
= 25°C  
S
L
R
–60  
–70  
T
A
3RD HARMONIC,  
5MHz INPUT  
–60  
–70  
–70  
2ND HARMONIC,  
5MHz INPUT  
–80  
–80  
–80  
3RD HARMONIC,  
1MHz INPUT  
–90  
–90  
–90  
–100  
–110  
–100  
–110  
–100  
–110  
2ND HARMONIC,  
1MHz INPUT  
V
= 3V, V = 2V  
V = 5V, V = 2V  
S IN P-P  
S
L
IN  
P-P  
R
= 800ꢀ, T = 25°C  
R = 800ꢀ, T = 25°C  
L A  
A
0
1
2
3
4
5
0.1  
1
10  
0.1  
1
10  
INPUT LEVEL (V  
)
FREQUENCY (MHz)  
FREQUENCY (MHz)  
P-P  
66005 G09  
66005 G07  
66005 G08  
66005fa  
4
LT6600-5  
TYPICAL PERFORMANCE CHARACTERISTICS  
Distortion vs Signal Level  
Distortion vs Input Common Mode  
Distortion vs Input Common Mode  
–40  
–50  
–40  
–50  
–60  
–70  
–80  
–40  
–50  
2ND HARMONIC,  
2ND HARMONIC,  
V
S
= 3V  
V = 3V  
S
3RD HARMONIC  
5MHz INPUT  
3RD HARMONIC,  
= 3V  
3RD HARMONIC,  
V = 3V  
S
V
S
2ND HARMONIC,  
= 5V  
2ND HARMONIC,  
V = 5V  
S
–60  
–60  
–70  
2ND HARMONIC  
5MHz INPUT  
V
S
3RD HARMONIC,  
= 5V  
3RD HARMONIC,  
= 5V  
–70  
V
V
S
S
3RD HARMONIC  
1MHz INPUT  
–80  
–80  
2ND HARMONIC  
1MHz INPUT  
–90  
–90  
–100  
–110  
–90  
GAIN = 4, PIN 7 = V /2  
GAIN = 1, PIN 7 = V /2  
S
–100  
–110  
–100  
–110  
S
V
=
5V  
2V 1MHz INPUT  
P-P  
S
L
2V 1MHz INPUT  
P-P  
R
= 800ꢀ, T = 25°C  
R = 800ꢀ, T = 25°C  
L A  
A
R
L
= 800ꢀ, T = 25°C  
A
1
2
3
5
–3  
–2  
–1  
0
1
2
3
–3  
–1  
0
1
2
3
0
4
–2  
INPUT COMMON MODE VOLTAGE  
RELATIVE TO PIN 7 (V)  
INPUT COMMON MODE VOLTAGE  
RELATIVE TO PIN 7 (V)  
66005 G12  
INPUT LEVEL (V  
)
P-P  
66005 G10  
66005 G11  
Transient Response, Differential  
Gain = 1, Single-Ended Input,  
Differential Output  
Power Supply Current  
vs Power Supply Voltage  
Distortion vs Temperature  
20  
0
36  
34  
32  
30  
28  
26  
24  
1dB PASSBAND GAIN  
COMPRESSION POINTS  
1MHz T = 25°C  
A
–
OUT  
200mV/DIV  
1MHz T = 85°C  
A
T
= 85°C  
A
3RD HARMONIC  
= 85°C  
–20  
–40  
–60  
–80  
–100  
–120  
T
A
+
OUT  
3RD HARMONIC  
= 25°C  
T
= 25°C  
A
200mV/DIV  
T
A
–
T
= –40°C  
A
2ND HARMONIC  
IN  
T
A
= 85°C  
500mV/DIV  
+
IN  
22  
20  
2ND HARMONIC  
T
= 25°C  
A
4
6
7
100ns/DIV  
0
1
2
3
5
6
2
4
8
10  
12  
1MHz INPUT LEVEL (V  
)
TOTAL SUPPLY VOLTAGE (V)  
P-P  
66005 G15  
66005 G13  
66005 G14  
Distortion  
vs Output Common Mode  
Input Referred Noise  
–40  
–50  
–60  
45  
40  
35  
30  
25  
20  
15  
10  
5
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
GAIN = 4  
INTEGRATED NOISE, GAIN = 1X  
INTEGRATED NOISE, GAIN = 4X  
NOISE DENSITY, GAIN = 1X  
NOISE DENSITY, GAIN = 4X  
PIN 7 = V /2  
S
T
= 25°C  
P-P  
= 800ꢀ  
A
0.5V 1MHz INPUT  
R
L
2ND HARMONIC, V = 3V  
S
3RD HARMONIC, V = 3V  
S
–70  
–80  
2ND HARMONIC, V = 5V  
S
3RD HARMONIC, V = 5V  
S
S
S
2ND HARMONIC, V  
3RD HARMONIC, V  
=
=
5V  
5V  
–90  
–100  
–110  
0
0.01  
–1.5 –1.0  
0
0.5 1.0 1.5 2.0 2.5  
–0.5  
0.1  
10  
100  
VOLTAGE PIN 2 TO PIN 7 (V)  
FREQUENCY (MHz)  
66005 G16  
66005 G17  
66005fa  
5
LT6600-5  
PIN FUNCTIONS  
–
+
IN and IN (Pins 1, 8): Input Pins. Signals can be ap-  
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.  
plied to either or both input pins through identical external  
resistors, R . The DC gain from differential inputs to the  
IN  
differential outputs is 806Ω/R .  
+
–
IN  
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  
modevoltageofthedifferentialoutputofthefilter.Pin2isa  
highimpedanceinput,whichcanbedrivenfromanexternal  
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
(Pin 7): The V  
pin is internally biased at mid-  
MID  
MID  
supply, see block diagram. For single supply operation  
the V pin should be bypassed with a quality 0.01μF  
MID  
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.  
+
–
V and V (Pins 3, 6): Power Supply Pins. For a single  
3.3Vor5Vsupply(Pin6grounded)aquality0.1μFceramic  
bypass capacitor is required from the positive supply pin  
(Pin 3) to the negative supply pin (Pin 6). The bypass  
BLOCK DIAGRAM  
R
IN  
+
+
–
–
V
IN  
V
OUT  
5
V
IN  
MID  
8
7
6
+
V
11k  
11k  
PROPRIETARY  
LOWPASS  
806ꢀ  
FILTER STAGE  
400ꢀ  
–
V
OP AMP  
400ꢀ  
400ꢀ  
+
+
OCM  
–
–
V
V
OCM  
+
+
–
–
400ꢀ  
806ꢀ  
1
2
3
4
66005 BD  
+
–
–
+
V
V
IN  
IN  
OCM  
V
OUT  
R
IN  
66005fa  
6
LT6600-5  
APPLICATIONS INFORMATION  
Interfacing to the LT6600-5  
is 2V for frequencies below 5MHz. The common mode  
P-P  
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  
(refer to the Distortion vs Input Common Mode Level  
graphs in the Typical Performance Characteristics).  
The LT6600-5 requires 2 equal external resistors, R , to  
IN  
set the differential gain to 806Ω/R . The inputs to the  
IN  
+
–
filter are the voltages V and V presented to these  
IN  
IN  
external components, Figure 1. The difference between  
+
–
V
and V is the differential input voltage. The aver-  
IN  
IN  
+
–
age of V and V  
Similarly,thevoltagesV  
is the common mode input voltage.  
IN  
IN  
+
–
andV  
appearingatPins4  
Figure2showshowtoACcouplesignalsintotheLT6600-5.  
In this instance, the input is a single-ended signal. AC  
coupling allows the processing of single-ended or dif-  
ferential signals with arbitrary common mode levels. The  
0.1μFcouplingcapacitorandthe806Ωgainsettingresistor  
form a high pass filter, attenuating signals below 2kHz.  
Larger values of coupling capacitors will proportionally  
reduce this highpass 3dB frequency.  
OUT  
OUT  
and 5 of the LT6600-5 are the filter outputs. The differ-  
+
–
ence between V  
and V  
is the differential output  
OUT  
OUT  
+
–
voltage. The average of V  
mode output voltage.  
and V  
is the common  
OUT  
OUT  
Figure 1 illustrates the LT6600-5 operating with a single  
3.3V supply and unity passband gain; the input signal is  
DC coupled. The common mode input voltage is 0.5V and  
the differential input voltage is 2V . The common mode  
In Figure 3 the LT6600-5 is providing 12dB of gain. The  
gain resistor has an optional 62pF in parallel to improve  
P-P  
output voltage is 1.65V and the differential output voltage  
3.3V  
0.1μF  
V
V
3
–
806ꢀ  
3
2
1
0
3
2
1
0
1
7
2
8
–
+
V
V
4
IN  
+
–
+
–
V
V
+
OUT  
V
OUT  
LT6600-5  
+
V
0.01μF  
IN  
V
OUT  
–
OUT  
5
+
IN  
806ꢀ  
6
t
t
–
66005 F01  
V
IN  
Figure 1  
3.3V  
3
0.1μF  
4
V
V
0.1μF  
0.1μF  
806ꢀ  
806ꢀ  
1
3
2
1
0
2
1
–
+
–
+
V
V
+
7
OUT  
V
V
OUT  
LT6600-5  
2
8
+
–
V
IN  
0.01μF  
OUT  
–
0
t
+
OUT  
5
V
+
IN  
6
–1  
66005 F02  
Figure 2  
62pF  
5V  
0.1μF  
4
V
V
3
200ꢀ  
1
7
2
8
–
3
3
V
V
–
IN  
IN  
+
+
–
V
V
OUT  
+
OUT  
LT6600-5  
2
1
0
2
1
V
0.01μF  
OUT  
–
V
OUT  
500mV (DIFF)  
P-P  
–
+
5
+
+
V
V
200ꢀ  
62pF  
IN  
6
t
t
0
+
–
2V  
66005 F03  
IN  
–
0.01μF  
Figure 3  
66005fa  
7
LT6600-5  
APPLICATIONS INFORMATION  
the passband flatness near 5MHz. The common mode  
output voltage is set to 2V.  
Figure5isalaboratorysetupthatcanbeusedtocharacter-  
izetheLT6600-5usingsingle-endedinstrumentswith50Ω  
source impedance and 50Ω input impedance. For a unity  
gain configuration the LT6600-5 requires a 806Ω source  
resistance yet the network analyzer output is calibrated  
for a 50Ω load resistance. The 1:1 transformer, 51.1Ω  
and 787Ω resistors satisfy the two constraints above.  
The transformer converts the single-ended source into a  
differential stimulus. Similarly, the output the LT6600-5  
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 LT6600-5 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 be-  
tween the transformer and analyzer input.  
Use Figure 4 to determine the interface between the  
LT6600-5 and a current output DAC. The gain, or “tran-  
simpedance,” is defined as A = V /I Ω. To compute  
OUT IN  
the transimpedance, use the following equation:  
806 •R1  
R1+R2  
A =  
Ω
By setting R1 + R2 = 806Ω, the gain equation reduces  
to A = R1Ω.  
The voltage at the pins of the DAC is determined by R1,  
R2, the voltage on Pin 7 and the DAC output current  
(IIN+ or IIN–). Consider Figure 4 with R1 = 49.9Ω and R2  
= 750Ω. The voltage at Pin 7 is 1.65V. The voltage at the  
DAC pins is given by:  
2.5V  
R1  
R1+R2+806 IN R1+R2  
= 51mV +I 46.8Ω  
R1•R2  
0.1μF  
V
DAC = VPIN7  
•
+I  
COILCRAFT  
TTWB-16A  
4:1  
COILCRAFT  
TTWB-1010  
NETWORK  
ANALYZER  
SOURCE  
NETWORK  
ANALYZER  
INPUT  
3
IN  
787ꢀ  
1:1  
1
7
2
8
402ꢀ  
–
4
+
–
+
50ꢀ  
I is IIN or IIN . The transimpedance in this example is  
LT6600-5  
IN  
51.1ꢀ  
50ꢀ  
402ꢀ  
50.3Ω.  
–
5
+
787ꢀ  
6
0.1μF  
66005 F05  
CURRENT  
3.3V  
OUTPUT  
0.1μF  
DAC  
–2.5V  
–
+
3
R2  
I
I
IN  
IN  
1
7
2
8
–
4
+
–
Figure 5  
+
V
V
OUT  
R1  
R1  
0.01μF  
R2  
LT6600-5  
Differential and Common Mode Voltage Ranges  
–
OUT  
5
+
The differential amplifiers inside the LT6600-5 contain  
circuitry to limit the maximum peak-to-peak differential  
voltage through the filter. 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  
6
66005 F04  
Figure 4  
Evaluating the LT6600-5  
2V and it becomes noticeable above 3.5V . This is  
P-P  
P-P  
The low impedance levels and high frequency operation  
of the LT6600-5 require some attention to the matching  
networks between the LT6600-5 and other devices. The  
previous examples assume an ideal (0Ω) source imped-  
ance and a large (1kΩ) load resistance. Among practi-  
cal examples where impedance must be considered is  
the evaluation of the LT6600-5 with a network analyzer.  
illustrated in Figure 6; the LTC6600-5 was configured with  
unity passband gain and the input of the filter was driven  
with a 1MHz signal. Because this voltage limiting takes  
place well before the output stage of the filter reaches the  
supply rails, the input/output behavior of the IC shown  
in Figure 6 is relatively independent of the power supply  
voltage.  
66005fa  
8
LT6600-5  
APPLICATIONS INFORMATION  
20  
the power supply level and gain setting (see “Electrical  
Characteristics”).  
1dB PASSBAND GAIN  
COMPRESSION POINTS  
1MHz T = 25°C  
A
0
–20  
1MHz T = 85°C  
A
3RD HARMONIC  
= 85°C  
Common Mode DC Currents  
T
A
3RD HARMONIC  
= 25°C  
–40  
T
InapplicationslikeFigure1andFigure3wheretheLT6600-5  
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 between input and  
output terminals. Minimize these currents to decrease  
power dissipation and distortion.  
A
–60  
–80  
2ND HARMONIC  
A
T
= 85°C  
–100  
–120  
2ND HARMONIC  
= 25°C  
T
A
4
6
7
0
1
2
3
5
1MHz INPUT LEVEL (V  
)
P-P  
Consider the application in Figure 3. Pin 7 sets the output  
commonmodevoltageofthe1stdifferentialamplifierinside  
the LT6600-5 (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  
combinationoftheinternal806Ωfeedbackresistorandthe  
external200Ωinputresistor.Theresulting2.5mAcommon  
mode DC current in each input path, must be absorbed by  
66005 F06  
Figure 6  
The two amplifiers inside the LT6600-5 have independent  
control of their output common mode voltage (see the  
“block diagram” section). The following guidelines will  
optimize the performance of the filter for single supply  
operation.  
+
–
the sources V and V . Pin 2 sets the common mode  
Pin 7 must be bypassed to an AC ground with a 0.01μF or  
highercapacitor.Pin7canbedrivenfromalowimpedance  
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.  
IN  
IN  
output voltage of the 2nd differential amplifier inside the  
LT6600-5, and therefore sets the common mode output  
voltage of the filter. Since in the example, Figure 3, Pin 2  
differsfromPin7by0.5V, anadditional1.25mA(0.625mA  
per side) of DC current will flow in the resistors coupling  
the 1st differential amplifier output stage to filter output.  
Thus, a total of 6.25mA 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  
than3.3VthevoltageatPin2canbesetabovemid-supply.  
The voltage on Pin 2 should not be more than 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 com-  
monmodecurrentsby36%.IfPin7isshortedtoPin2,the  
common mode output voltage of both op amp stages will  
be 2V and the resulting DC current will be 4mA. Of course,  
by AC coupling the inputs of Figure 3 and shorting Pin 7  
to Pin 2, the common mode DC current is eliminated.  
Noise  
The noise performance of the LT6600-5 can be evaluated  
with the circuit of Figure 7.  
The LT6600-5 was designed to process a variety of input  
signals including signals centered around the mid-sup-  
ply 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  
Given the low noise output of the LT6600-5 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.  
+
–
average of V and V  
in Figure 1) is determined by  
IN  
IN  
66005fa  
9
LT6600-5  
APPLICATIONS INFORMATION  
45  
40  
35  
30  
25  
20  
15  
10  
5
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
2.5V  
INTEGRATED NOISE, GAIN = 1X  
INTEGRATED NOISE, GAIN = 4X  
NOISE DENSITY, GAIN = 1X  
NOISE DENSITY, GAIN = 4X  
0.1μF  
SPECTRUM  
COILCRAFT  
ANALYZER  
R
3
TTWB-1010  
1:1  
IN  
V
IN  
INPUT  
1
7
2
8
25ꢀ  
25ꢀ  
–
4
+
LT6600-5  
50ꢀ  
–
5
+
0.1μF  
R
IN  
6
66005 F07  
–2.5V  
0
0.01  
0.1  
10  
100  
Figure 7  
FREQUENCY (MHz)  
66005 G08  
Example: With the IC removed and the 25Ω resistors  
Figure 8  
grounded, measure the total integrated noise (e ) of the  
S
Conversely,ifeachoutputismeasuredindividuallyandthe  
noise power added together, the resulting calculated noise  
level will be higher than the true differential noise.  
spectrum analyzer from 10kHz to 5MHz. With the IC in-  
serted, thesignalsource(V )disconnected, andtheinput  
IN  
resistors grounded, measure the total integrated noise  
out of the filter (e ). With the signal source connected,  
O
Power Dissipation  
set the frequency to 1MHz and adjust the amplitude until  
V measures 100mV . Measure the output amplitude,  
IN  
OUT  
P-P  
The LT6600-5 amplifiers 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 LT6600-5 package has Pin 6 fused  
to 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 cop-  
per, a total of 660 square millimeters connected to Pin 6  
of the LT6600-5 (330 square millimeters on each side of  
V
, and compute the passband gain A = V /V . Now  
OUT IN  
compute the input referred integrated noise (e ) as:  
IN  
(eO)2 –(eS)2  
eIN =  
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 LT6600-5 with R = 806Ω and 200Ω  
IN  
the PC board) will result in a thermal resistance, θ , of  
JA  
using the fixture of Figure 7 (the instrument noise has  
about 85°C/W. Without extra metal trace connected to the  
been subtracted from the results).  
–
V pin to provide a heat sink, the thermal resistance will  
Table 1. Noise Performance  
INPUT REFERRED  
be around 105°C/W. Table 2 can be used as a guide when  
considering thermal resistance.  
PASSBAND  
GAIN (V/V)  
INTEGRATED NOISE INPUT REFERRED  
R
10kHz TO 10MHz  
NOISE dBm/Hz  
IN  
Table 2. LT6600-5 SO-8 Package Thermal Resistance  
COPPER AREA  
4
2
1
200Ω  
402Ω  
806Ω  
24μV  
38μV  
69μV  
–149  
RMS  
RMS  
RMS  
–145  
TOPSIDE  
BACKSIDE BOARD AREA  
THERMAL RESISTANCE  
(JUNCTION-TO-AMBIENT)  
2
2
2
(mm )  
(mm )  
(mm )  
–140  
1100  
330  
35  
1100  
330  
35  
2500  
2500  
2500  
2500  
2500  
65°C/W  
85°C/W  
95°C/W  
100°C/W  
105°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.  
35  
0
0
0
66005fa  
10  
LT6600-5  
APPLICATIONS INFORMATION  
Junction temperature, T , is calculated from the ambient  
ent temperature is maximum. To compute the junction  
temperature, measure the supply current under these  
worst-case conditions, estimate the thermal resistance  
from Table 2, then apply the equation for TJ. For example,  
using the circuit in Figure 3 with DC differential input volt-  
age of 250mV, a differential output voltage of 1V, 1kΩ load  
resistanceandanambienttemperatureof85°C,thesupply  
current (current into Pin 3) measures 32.2mA. Assuming  
a PC board layout with a 35mm2 copper trace, the θJA is  
100°C/W. The resulting junction temperature is:  
J
temperature, T , and power dissipation, P . The power  
A
D
dissipation is the product of supply voltage, V , and  
S
supply current, I . Therefore, the junction temperature  
S
is given by:  
T = T + (P • θ ) = T + (V • I • θ )  
J
A
D
JA  
A
S
S
JA  
where the supply current, I , is a function of signal level,  
S
load impedance, temperature and common mode volt-  
ages.  
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 Applications Information regarding common mode  
DC currents), the load impedance is small and the ambi-  
T = T + (P • θ ) = 85 + (5 • 0.0322 • 100) = 101°C  
J
A
D
JA  
When using higher supply voltages or when driving small  
impedances, more copper may be necessary to keep T  
below 150°C.  
J
PACKAGE DESCRIPTION  
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  
66005fa  
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 representa-  
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.  
11  
LT6600-5  
TYPICAL APPLICATION  
Dual, Matched, 6th Order, 5MHz Lowpass Filter  
Single-Ended Input (IIN and QIN) and Differential Output (IOUT and QOUT  
)
+
V
I
0.1μF  
IN  
+
0.1μF  
V
806ꢀ  
806ꢀ  
3
1
4
–
1
2
3
4
5
6
7
8
16  
15  
14  
13  
12  
11  
10  
9
+
+
+
7
2
8
V
V
LT1568  
LT6600-5  
249ꢀ  
249ꢀ  
249ꢀ  
249ꢀ  
249ꢀ  
249ꢀ  
I
OUT  
Q
INVA  
INVB  
IN  
–
6
+
SA  
SB  
5
0.1μF  
OUTA OUTB  
OUTA OUTB  
GNDA GNDB  
–
V
I
Q
OUT  
Q
IN  
OUT  
+
V
0.1μF  
4
GAIN =  
OR  
= 1  
NC  
–
EN  
–
I
IN  
V
V
806ꢀ  
3
1
0.1μF  
–
+
7
2
8
LT6600-5  
–
Q
V
OUT  
–
6
+
5
806ꢀ  
0.1μF  
66005 TA02  
–
V
Amplitude Response  
Transient Response  
12  
0
OUTPUT  
OR Q  
–12  
–24  
–36  
–48  
–60  
–72  
–84  
–96  
–108  
(I  
OUT  
)
OUT  
200mV/DIV  
INPUT  
(I OR Q  
IN IN  
)
500mV/DIV  
66005 TA02c  
100ns/DIV  
100  
1
10  
40  
FREQUENCY (Hz)  
66005 TA02b  
RELATED PARTS  
PART NUMBER  
LTC®1565-31  
LTC1566-1  
LT1567  
DESCRIPTION  
COMMENTS  
650kHz Linear Phase Lowpass Filter  
Low Noise, 2.3MHz Lowpass Filter  
Continuous Time, SO8 Package, Fully Differential  
Continuous Time, SO8 Package, Fully Differential  
1.4nV/√Hz Op Amp, MSOP Package, Differential Output  
Very Low Noise, High Frequency Filter Building Block  
Very Low Noise, 4th Order Building Block  
LT1568  
Lowpass and Bandpass Filter Designs Up to 10MHz,  
Differential Outputs  
LTC1569-7  
LT6600-2.5  
LT6600-10  
LT6600-20  
Linear Phase, DC Accurate, Tunable 10th Order Lowpass One External Resistor Sets Filter Cutoff Frequency, Differential Inputs  
Filter  
Very Low Noise, Differential Amplifier  
and 2.5MHz Lowpass Filter  
Adjustable Output Common Mode Voltage  
Adjustable Output Common Mode Output Voltage  
Adjustable Output Common Mode Voltage  
Very Low Noise, Differential Amplifier  
and 10MHz Lowpass Filter  
Very Low Noise, Differential Amplifier  
and 20MHz Lowpass Filter  
66005fa  
LT 0408 REV A • PRINTED IN USA  
LinearTechnology Corporation  
1630 McCarthy Blvd., Milpitas, CA 95035-7417  
12  
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© LINEAR TECHNOLOGY CORPORATION 2004  
(408) 432-1900 FAX: (408) 434-0507 www.linear.com  

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