LT6600CDF-2.5#PBF_技术文档

LT6600-2.5

Very Low Noise, Differential

Ampliﬁer and 2.5MHz Lowpass Filter

FEATURES

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

internallyset. TheLT6600-2.5alsoprovidesthenecessary

levelshiftingtosetitsoutputcommonmodevoltagetoac-

commodate the reference voltage requirements of A/Ds.

n

0.6dB ꢀMaxꢁ ꢂipple 4th Order Lowpass Filter with

2.5MHz Cutoff

n

Programmable Differential Gain via Two External

ꢂesistors

Adjustable Output Common Mode Voltage

Operates and Speciﬁed with 3V, 5V, 5V Supplies

86dB S/N with 3V Supply and 1V

Low Distortion, 1V

n

Output

ꢂMS

, 800Ω Load

ꢂMS

1MHz: 95dBc 2nd, 88dBc 3rd

Fully Differential Inputs and Outputs

Compatible with Popular Differential Ampliﬁer

Pinouts

SO-8 and DFN-12 Packages

n

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.

n

APPLICATIONS

n

High Speed ADC Antialiasing and DAC Smoothing in

Networking or Cellular Basestation Applications

n

High Speed Test and Measurement Equipment

The LT6600-2.5 also features low voltage operation. The

differentialdesignprovidesoutstandingperformancefora

n

Medical Imaging

n

Drop-in ꢂeplacement for Differential Ampliﬁers

4V signal level while the part operates with a single 3V

P-P

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.

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.

(S8 Pin Numbers Shown)

TYPICAL APPLICATION

DAC Output Filter

DAC Output Spectrum

LT6600-2.5 Output Spectrum

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

5V

0.1μF

5V

BASEBAND SIGNAL

52.3Ω

1580Ω

3

1

LADCOM

–

4

+

–

V

I

OUT

7

2

+

OUT A

16-BIT 4kHz to 2.5MHz

DISCꢂETE MULTI-TONE

SIGNAL AT 50MSPS

LT6600-2.5

LTC1668

DAC OUTPUT IMAGE

I

V

–

6

OUT B

8

OUT

5

+

CLK

0.1μF

–5V 50MHz

–5V

660025 TA01a

0

12 24 36 48 60 72 84 96 108 120

0

12 24 36 48 60 72 84 96 108 120

FꢂEQUENCY ꢀMHzꢁ

FREQUENCY (MHz)

660025 TA01b

660025 TA01c

660025fe

1

LT6600-2.5

(Note 1)

ABSOLUTE MAXIMUM RATINGS

Total Supply Voltage .................................................11V

Input Current ꢀNote 8ꢁ.......................................... 10mA

Operating Temperature ꢂange ꢀNote 6ꢁ.... –40°C to 85°C

Speciﬁed Temperature ꢂange ꢀNote 7ꢁ .... –40°C to 85°C

Junction Temperature ........................................... 150°C

Storage Temperature ꢂange................... –65°C to 150°C

Lead Temperature ꢀSoldering, 10 secꢁ .................. 300°C

PIN CONFIGURATION

TOP VIEW

+

–

1

2

3

4

5

6

12 IN

IN

–

+

IN

1

2

3

4

8

7

6

5

IN

NC

V

NC

11

10

9

V

MID

OCM

+

V

OCM

MID

–

12

–

V

+

V

–

8

NC

+

–

OUT

–

7

OUT

S8 PACKAGE

8-LEAD PLASTIC SO

= 150°C, θ = 100°C/W

DF PACKAGE

12-LEAD ꢀ4mm × 4mmꢁ PLASTIC DFN

T

JMAX

JA

T

= 150°C, θ = 43°C/W, θ = 4°C/W

JA JC

JMAX

–

EXPOSED PAD ꢀPIN 13ꢁ IS V , MUST BE SOLDEꢂED TO PCB

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

TAPE AND REEL

PART MARKING* PACKAGE DESCRIPTION

SPECIFIED TEMPERATURE RANGE

LT6600CS8-2.5#TꢂPBF

LT6600IS8-2.5#TꢂPBF

LT6600CDF-2.5#TꢂPBF

LT6600IDF-2.5#TꢂPBF

TAPE AND REEL

660025

600I25

8-Lead Plastic SO

0°C to 70°C

–40°C to 85°C

60025

0°C to 70°C

12-Lead ꢀ4mm × 4mmꢁ Plastic DFN

PACKAGE DESCRIPTION

8-Lead Plastic SO

60025

–40°C to 85°C

PART MARKING

660025

600I25

SPECIFIED TEMPERATURE RANGE

0°C to 70°C

LT6600CS8-2.5#Tꢂ

LT6600IS8-2.5#Tꢂ

LT6600IS8-2.5

8-Lead Plastic SO

–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

ELECTRICAL CHARACTERISTICS

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 = 3V

CONDITIONS

MIN

–0.5

–0.15

–0.2

–0.6

TYP

0.1

0

MAX

0.4

UNITS

dB

V

IN

V

IN

V

IN

V

IN

= 2V , f = DC to 260kHz

P-P IN

S

l

ꢂ

= 1580Ω

= 2V , f = 700kHz ꢀGain ꢂelative to 260kHzꢁ

0.1

dB

IN

P-P IN

= 2V , f = 1.9MHz ꢀGain ꢂelative to 260kHzꢁ

0.2

0.1

0.6

dB

P-P IN

= 2V , f = 2.2MHz ꢀGain ꢂelative to 260kHzꢁ

0.5

dB

P-P IN

660025fe

2

LT6600-2.5

ELECTRICAL CHARACTERISTICS ^Thel 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

CONDITIONS

MIN

TYP

–0.9

–34

–51

–0.1

0

MAX

0

UNITS

dB

l

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

V

IN

= 2V , f = 2.5MHz ꢀGain ꢂelative to 260kHzꢁ

–2.1

P-P IN

= 2V , f = 7.5MHz ꢀGain ꢂelative to 260kHzꢁ

–31

dB

P-P IN

= 2V , f = 12.5MHz ꢀGain ꢂelative to 260kHzꢁ

dB

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

dB

S

P-P IN

l

ꢂ

IN

= 1580Ω

= 2V , f = 700kHz ꢀGain ꢂelative to 260kHzꢁ

dB

P-P IN

= 2V , f = 2.2MHz ꢀGain ꢂelative to 260kHzꢁ

0.2

dB

P-P IN

= 2V , f = 2.2MHz ꢀGain ꢂelative to 260kHzꢁ

0.1

dB

P-P IN

= 2V , f = 2.5MHz ꢀGain ꢂelative to 260kHzꢁ

–0.9

–34

–51

–0.1

dB

P-P IN

= 2V , f = 7.5MHz ꢀGain ꢂelative to 260kHzꢁ

–31

dB

P-P IN

= 2V , f = 12.5MHz ꢀGain ꢂelative to 260kHzꢁ

dB

P-P IN

Filter Gain, V = 5V

= 2V , f = DC to 260kHz

–0.6

0.4

dB

S

P-P IN

Filter Gain, ꢂ = 402Ω

V

= 0.5V , f = DC to 260kHz, V = 3V

11.3

11.2

11.8

11.7

12.3

12.2

dB

IN

P-P IN

S

= 0.5V , f = DC to 260kHz, V = 5V

P-P IN

S

= 0.5V , f = DC to 260kHz, V = 5V

P-P IN

S

Filter Gain Temperature Coefﬁcient ꢀNote 2ꢁ

f

= 260kHz, V = 2V

P-P

780

51

ppm/°C

IN

Noise

Noise BW = 10kHz to 2.5MHz

1MHz, 1V , ꢂ = 800Ω

ꢃV

ꢂMS

Distortion ꢀNote 4ꢁ

2nd Harmonic

3rd Harmonic

95

88

dBc

ꢂMS

L

l

Differential Output Swing

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

S

P-P DIFF

V = 3V

l

Input Bias Current

–35

–15

ꢃA

l

Input ꢂeferred Differential Offset

ꢂ

IN

= 1580Ω, Differential Gain = 1V/V

V = 3V

5

25

30

35

mV

S

V = 5V

S

V = 5V

S

l

ꢂ

= 402Ω, Differential Gain = 4V/V

V = 3V

3

13

16

20

mV

IN

S

V = 5V

S

V = 5V

S

Differential Offset Drift

10

ꢃV/°C

l

Input Common Mode Voltage ꢀNote 3ꢁ

Differential Input = 500mV

IN

,

V = 3V

0.0

–2.5

1.5

3.0

1.0

V

P-P

S

ꢂ

≥ 402Ω

V = 5V

S

V = 5V

S

l

Output Common Mode Voltage ꢀNote 5ꢁ

Differential Input = 2V

Pin 7 = Open

,

V = 3V

1.0

1.5

–1.0

1.5

3.0

2.0

V

P-P

S

V = 5V

S

V = 5V

S

l

Output Common Mode Offset

ꢀwith ꢂespect to Pin 2ꢁ

V = 3V

–25

–30

–55

10

5

–10

45

35

mV

S

V = 5V

S

V = 5V

S

Common Mode ꢂejection ꢂatio

63

dB

l

Voltage at V

ꢀPin 7ꢁ

V = 5V ꢀS8ꢁ

2.46

2.45

2.51

1.5

2.55

2.56

V

MID

S

V = 5V ꢀDFNꢁ

S

V = 3V

S

l

V

Input ꢂesistance

Bias Current

4.3

5.7

7.7

kΩ

MID

l

V

OCM

= V

= V /2

V = 5V

S

–15

–10

–3

μA

OCM

MID

S

V = 3V

Power Supply Current

V = 3V, V = 5V

26

30

33

36

mA

S

l

V = 3V, V = 5V

S

V = 5V

28

S

660025fe

3

LT6600-2.5

ELECTRICAL CHARACTERISTICS

Note 1: Stresses beyond those listed under Absolute Maximum ꢂatings

may cause permanent damage to the device. Exposure to any Absolute

Maximum ꢂating 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-2.5 is guaranteed functional over the operating

temperature range of –40°C to 85°C.

Note 2: This is the temperature coefﬁcient of the internal feedback

resistors assuming a temperature independent external resistor ꢀꢂ ꢁ.

Note 3: The input common mode voltage is the average of the voltages

IN

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.

applied to the external resistors ꢀꢂ ꢁ. Speciﬁcation guaranteed for ꢂ

IN

≥ 402Ω. For 5V supplies, the minimum input common mode voltage is

guaranteed by design to reach –5V.

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 single-ended stimulus.

The input common mode voltage, the voltage at V , and the voltage at

OCM

V

are equal to one half of the total power supply voltage.

MID

TYPICAL PERFORMANCE CHARACTERISTICS

Amplitude Response

Passband Gain and Group Delay

12

0

12

11

10

9

320

300

280

260

240

220

200

180

160

140

120

1

0

320

300

280

260

240

220

200

180

160

140

120

V

=

IN

2.5V

S

ꢂ

= 1580ꢄ

GAIN = 1

–1

–2

–3

–4

–5

–6

–7

–8

–9

–12

–24

–36

–48

–60

–72

–84

–96

8

7

6

5

V

= 5V

IN

V

= 5V

IN

S

4

ꢂ

= 402ꢄ

ꢂ

= 1580ꢄ

GAIN = 4

GAIN = 1

3

T

= 25°C

T

= 25°C

A

2

100k

1M

10M

50M

0.5 0.75 1.0 1.25

2.0 2.25 2.5 2.75

3.0

1.5 1.75

0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 2.75 3.0

FꢂEQUENCY ꢀHzꢁ

FꢂEQUENCY ꢀMHzꢁ

660025 G01

660025 G03

660025 G02

Output Impedance

vs Frequency (OUT⁺or OUT^–)

CMRR

PSRR

100

10

1

90

80

70

60

50

40

30

20

10

0

110

+

V

TO

DIFFEꢂENTIAL OUT

= 3V

V

= 1V

= 5V

IN

S

P-P

100

90

80

70

60

50

40

V

ꢂ

= 1580ꢄ

S

GAIN = 1

0.1

100k

1M

10M

100M

1k

10k

100k

1M

10M

100M

1k

10k

100k

1M

10M

100M

FꢂEQUENCY ꢀHzꢁ

660025 G04

660025 G06

660025 G05

660025fe

4

LT6600-2.5

TYPICAL PERFORMANCE CHARACTERISTICS

Distortion vs Frequency

–60

–70

–60

–70

DIFFEꢂENTIAL INPUT,

2ND HAꢂMONIC

DIFFEꢂENTIAL INPUT,

3ꢂD HAꢂMONIC

SINGLE-ENDED INPUT,

2ND HAꢂMONIC

SINGLE-ENDED INPUT,

3ꢂD HAꢂMONIC

DIFFEꢂENTIAL INPUT,

2ND HAꢂMONIC

DIFFEꢂENTIAL INPUT,

3ꢂD HAꢂMONIC

SINGLE-ENDED INPUT,

2ND HAꢂMONIC

SINGLE-ENDED INPUT,

3ꢂD HAꢂMONIC

–80

–90

V

= 2V

P-P

V

= 2V

= 3V

IN

S

L

IN

S

L

P-P

–100

–110

–100

–110

V

= 5V

= 800ꢄ AT

ꢂ

= 800ꢄ AT

EACH OUTPUT

0.1

1

10

0.1

1

10

FꢂEQUENCY ꢀMHzꢁ

660025 G08

660025 G07

Distortion vs Frequency

Distortion vs Signal Level

–40

–50

–60

–70

DIFFEꢂENTIAL INPUT,

2ND HAꢂMONIC

DIFFEꢂENTIAL INPUT,

3ꢂD HAꢂMONIC

SINGLE-ENDED INPUT,

2ND HAꢂMONIC

SINGLE-ENDED INPUT,

3ꢂD HAꢂMONIC

2ND HAꢂMONIC,

DIFFEꢂENTIAL INPUT

3ꢂD HAꢂMONIC,

DIFFEꢂENTIAL INPUT

2ND HAꢂMONIC,

SINGLE-ENDED INPUT

3ꢂD HAꢂMONIC,

SINGLE-ENDED INPUT

–60

–80

–70

–80

–90

V

= 2V

V

= 3V

IN

S

P-P

S

–100

–110

=

5V

F = 1MHz

= 800ꢄ AT

–100

–110

ꢂ

= 800ꢄ AT

ꢂ

L

EACH OUTPUT

0

1

2

3

4

5

6

0.1

1

10

FꢂEQUENCY ꢀMHzꢁ

INPUT LEVEL ꢀV

ꢁ

P-P

660025 G10

660025 G09

Distortion vs Signal Level

–40

–50

–40

–50

2ND HAꢂMONIC,

DIFFEꢂENTIAL INPUT

3ꢂD HAꢂMONIC,

DIFFEꢂENTIAL INPUT

2ND HAꢂMONIC,

SINGLE-ENDED INPUT

3ꢂD HAꢂMONIC,

SINGLE-ENDED INPUT

2ND HAꢂMONIC,

DIFFEꢂENTIAL INPUT

3ꢂD HAꢂMONIC,

DIFFEꢂENTIAL INPUT

2ND HAꢂMONIC,

SINGLE-ENDED INPUT

3ꢂD HAꢂMONIC,

SINGLE-ENDED INPUT

–60

–70

–80

–90

V

=

5V

F = 1MHz

= 800ꢄ AT

V

= 5V

S

F = 1MHz

= 800ꢄ AT

–100

–110

–100

–110

ꢂ

L

EACH OUTPUT

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

INPUT LEVEL ꢀV

ꢁ

P-P

INPUT LEVEL ꢀV

ꢁ

P-P

660025 G12

660025 G11

660025fe

5

LT6600-2.5

TYPICAL PERFORMANCE CHARACTERISTICS

Distortion

vs Input Common Mode Level

Distortion

vs Input Common Mode Level

–40

–50

–40

–50

2V 1MHz INPUT

2ND HAꢂMONIC,

= 3V

2ND HAꢂMONIC,

P-P

ꢂ

= 1580ꢄ

V

= 3V

IN

S

GAIN = 1

3ꢂD HAꢂMONIC,

= 3V

3ꢂD HAꢂMONIC,

= 3V

V

S

2ND HAꢂMONIC,

= 5V

–60

2ND HAꢂMONIC,

= 5V

–60

V

S

3ꢂD HAꢂMONIC,

= 5V

3ꢂD HAꢂMONIC,

= 5V

–70

V

S

–80

–90

–100

–110

2V 1MHz INPUT, ꢂ = 402ꢄ, GAIN = 4

P-P

IN

–110

–3

–2

–1

0

1

2

3

–3

–2

–1

0

1

2

3

INPUT COMMON MODE VOLTAGE ꢂELATIVE TO V

ꢀVꢁ

INPUT COMMON MODE VOLTAGE ꢂELATIVE TO V

ꢀVꢁ

MID

660025 G13

660025 G14

Distortion

vs Output Common Mode Level

Supply Current

vs Total Supply Voltage

32

30

28

26

24

22

20

18

16

–40

–50

2ND HAꢂMONIC,

= 3V

V

S

T

= 85°C

= 25°C

A

3ꢂD HAꢂMONIC,

= 3V

V

S

2ND HAꢂMONIC,

= 5V

–60

V

S

3ꢂD HAꢂMONIC,

= 5V

–70

V

S

2ND HAꢂMONIC,

5V

3ꢂD HAꢂMONIC,

5V

–80

V

=

S

V

=

S

T

= –40°C

–90

A

–100

2V 1MHz INPUT, ꢂ = 1580ꢄ, GAIN = 1

P-P

IN

–110

2

3

4

5

6

7

8

9

10

–1.5 –1.0 –0.5

0

2.0 2.5

0.5 1.0 1.5

TOTAL SUPPLY VOLTAGE ꢀVꢁ

VOLTAGE V

TO V

ꢀVꢁ

MID

OCM

660025 G16

660025 G15

Transient Response Gain = 1

V

+

OUT

50mV/DIV

DIFFEꢂENTIAL

INPUT

200mV/DIV

660025 G17

500ns/DIV

660025fe

6

LT6600-2.5

(DFN/SO)

PIN FUNCTIONS

–

+

IN and IN (Pins 1, 12/Pins 1, 8): Input Pins. Signals can

should be as close as possible to the IC. For dual supply

+

–

be applied to either or both input pins through identical

applications, bypass V to ground and V to ground with

a quality 0.1ꢃF ceramic capacitor.

externalresistors,ꢂ .TheDCgainfromdifferentialinputs

IN

to the differential outputs is 1580Ω/ꢂ .

+

–

IN

OUT and OUT (Pins 6, 7/Pins 4, 5): Output Pins. These

aretheﬁlterdifferentialoutputs.Eachpincandrivea100Ω

and/or 50pF load to AC ground.

NC (Pins 2, 5, 11/NA): No Connection

V

OCM

(Pin3/Pin2):DCCommonModeꢂeferenceVoltage-

for the 2nd Filter Stage. Its value programs the common

mode voltage of the differential output of the ﬁlter. This

is a high impedance input, which can be driven from an

V

(Pin 10/Pin 7): The V

pin is internally biased at

MID

mid-supply, see Block Diagram. For single supply op-

eration, the V

pin should be bypassed with a quality

MID

–

external voltage reference, or it can be tied to V

on the

0.01ꢃFceramiccapacitortoV . Fordualsupplyoperation,

MID

PCboard.V

shouldbebypassedwitha0.01ꢃFceramic

V

MID

can be bypassed or connected to a high quality DC

OCM

capacitor unless it is connected to a ground plane.

ground. A ground plane should be used. A poor ground

will increase noise and distortion. V sets the output

+

–

MID

V and V (Pins 4, 8, 9/Pins 3, 6): Power Supply Pins. For

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.

–

a single 3.3V or 5V supply ꢀV groundedꢁ a quality 0.1ꢃF

ceramic bypass capacitor is required from the positive

+

–

supplypinꢀV ꢁtothenegativesupplypinꢀV ꢁ. Thebypass

BLOCK DIAGRAM

ꢂ

IN

+

–

V

IN

V

OUT

V

IN

MID

+

V

11k

PꢂOPꢂIETAꢂY

LOWPASS

FILTEꢂ STAGE

1580ꢄ

800ꢄ

–

V

OP AMP

800ꢄ

+

OCM

–

V

OCM

+

–

800ꢄ

1580ꢄ

660025 BD

–

+

V

IN

OCM

V

OUT

ꢂ

IN

660025fe

7

LT6600-2.5

APPLICATIONS INFORMATION

Interfacing to the LT6600-2.5

DC-coupled. The common mode input voltage is 0.5V, and

the differential input voltage is 2V . The common mode

P-P

Note: The referenced pin numbers correspond to the S8

package. See the Pin Functions for the equivalent DFN-12

package pin numbers.

output voltage is 1.65V, and the differential output voltage

is2V forfrequenciesbelow2.5MHz.Thecommonmode

P-P

output voltage is determined by the voltage at V

. Since

OCM

The LT6600-2.5 requires two equal external resistors, ꢂ ,

V

is shorted to V , the output common mode is the

IN

OCM

MID

to set the differential gain to 1580Ω/ꢂ . The inputs to the

mid-supply voltage. In addition, the common mode input

IN

+

–

ﬁlter are the voltages V and V presented to the see

voltage can be equal to the mid-supply voltage of V

.

IN

MID

external components, Figure 1. The difference between

Figure2showshowtoACcouplesignalsintotheLT6600-2.5.

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 0.1ꢃF coupling capacitor and the 1580Ω gain set-

ting resistor form a highpass ﬁlter, attenuating signals

below 1kHz. Larger values of coupling capacitors will

proportionally reduce this highpass 3dB frequency.

+

–

V

and V is the differential input voltage. The aver-

IN

+

–

age of V and V is the common mode input voltage.

IN

+

–

Similarly,thevoltagesV

andV

appearingatPins4

OUT

and 5 of the LT6600-2.5 are the ﬁlter outputs. The differ-

+

–

ence between V

and V

is the differential output

OUT

+

–

voltage. The average of V

mode output voltage.

and V

is the common

OUT

Figure 1 illustrates the LT6600-2.5 operating with a single

3.3V supply and unity passband gain; the input signal is

In Figure 3 the LT6600-2.5 is providing 12dB of gain. The

common mode output voltage is set to 2V.

3.3V

0.1μF

V

3

–

1580ꢄ

3

2

1

0

3

2

1

0

1

7

2

8

–

+

V

4

IN

+

–

+

–

V

+

OUT

V

OUT

LT6600-2.5

+

V

0.01μF

1580ꢄ

IN

V

OUT

–

OUT

5

+

IN

6

t

–

660025 F01

V

IN

Figure 1. (S8 Pin Numbers)

3.3V

0.1μF

V

0.1μF

3

1580Ω

1

7

2

8

3

2

1

0

2

1

–

4

+

–

V

+

OUT

V

OUT

LT6600-2.5

+

V

IN

0.01μF

–

OUT

–

0

t

+

OUT

5

V

+

IN

1580Ω

6

t

–1

660025 F02

Figure 2. (S8 Pin Numbers)

5V

0.1μF

V

3

402ꢄ

1

–

3

2

1

0

V

–

4

IN

+

–

+

–

V

OUT

+

7

2

8

OUT

LT6600-2.5

2

1

V

0.01μF

402ꢄ

OUT

V

OUT

500mV ꢀDIFFꢁ

P-P

–

+

5

V

IN

+

V

IN

6

t

660025 F03

0

–

+

2V

IN

–

Figure 3. (S8 Pin Numbers)

660025fe

8

LT6600-2.5

APPLICATIONS INFORMATION

Use Figure 4 to determine the interface between the

LT6600-2.5 and a current output DAC. The gain, or “trans-

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

402Ω sourceresistance yet the networkanalyzer output is

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 impedanceꢁ 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.

impedance,” is deﬁned as A = V /I . To compute the

OUT IN

transimpedance, use the following equation:

1580 •R1

A =

Ω

( )

R1+R2

(

)

By setting ꢂ1 + ꢂ2 = 1580Ω, the gain equation reduces

to A = ꢂ1ꢀΩꢁ.

The voltage at the pins of the DAC is determined by ꢂ1,

ꢂ2, the voltage on V

and the DAC output current.

MID

Consider Figure 4 with ꢂ1 = 49.9Ω and ꢂ2 = 1540Ω. The

voltage at V , for V = 3.3V, is 1.65V. The voltage at the

MID

S

DAC pins is given by:

R1

R1•R2

R1+R2

V_DAC= V_PIN7

•

+I •

IN

R1+R2+1580

= 26mV +I • 48.3Ω

IN

Differential and Common Mode Voltage Ranges

+

–

Therail-to-railoutputstageoftheLT6600-2.5canprocess

large differential signal levels. On a 3V supply, the output

I is I or I . The transimpedance in this example is

IN

49.6Ω.

IN

signal can be 5.1V . Similarly, a 5V supply can support

P-P

Evaluating the LT6600-2.5

signals as large as 8.8V . To prevent excessive power

P-P

dissipation in the internal circuitry, the user must limit

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 ꢀ0Ωꢁ source imped-

ance and a large ꢀ1kΩꢁ load resistance. Among practical

examples where impedance must be considered is the

evaluation of the LT6600-2.5 with a network analyzer.

differential signal levels to 9V

.

P-P

The two ampliﬁers inside the LT6600-2.5 have indepen-

dent control of their output common mode voltage ꢀsee

the Block Diagram sectionꢁ. The following guidelines will

optimize the performance of the ﬁlter.

2.5V

CUꢂꢂENT

OUTPUT

DAC

0.1μF

3.3V

COILCꢂAFT

TTWB-16A

4:1

COILCꢂAFT

TTWB-1010

0.1μF

NETWOꢂK

ANALYZEꢂ

SOUꢂCE

NETWOꢂK

ANALYZEꢂ

INPUT

3

388ꢄ

1:1

1

7

2

8

402ꢄ

–

3

ꢂ2

–

4

I

IN

1

7

2

8

+

–

4

+

–

50ꢄ

V

+

LT6600-2.5

OUT

53.6ꢄ

50ꢄ

ꢂ1

+

402ꢄ

0.01μF

LT6600-2.5

–

5

+

–

IN

5

388ꢄ

+

6

0.1μF

660025 F04

660025 F05

6

+

–

ꢂ1

V

– V

1580 • ꢂ1

ꢂ1 + ꢂ2

OUT

–

=

I

– I

IN

–2.5V

Figure 4. (S8 Pin Numbers)

Figure 5. (S8 Pin Numbers)

660025fe

9

LT6600-2.5

APPLICATIONS INFORMATION

The LT6600-2.5 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 1ꢁ.

The range of allowable input common mode voltage ꢀthe

V

can be allowed to ﬂoat, but it must be bypassed to

MID

an AC ground with a 0.01ꢃF capacitor or some instability

maybeobserved.V canbedrivenfromalowimpedance

MID

–

source, provided it remains at least 1.5V above V and at

+

least 1.5V below V . An internal resistor divider sets the

+

–

average of V and V in Figure 1ꢁ is determined by

voltage of V . While the internal 11k resistors are well

IN

MID

the power supply level and gain setting ꢀsee Electrical

Characteristicsꢁ.

matched, their absolute value can vary by 20ꢅ. This

should be taken into consideration when connecting an

external resistor network to alter the voltage of V

.

MID

Common Mode DC Currents

V

can be shorted to V

for simplicity. If a different

OCM

MID

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,

DCcurrentswillbegeneratedthroughtheDCpathbetween

input and output terminals. Minimize these currents to

decrease power dissipation and distortion.

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 must be less than or equal

OCM

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 can be set above

OCM

mid-supply, as shown in Table 1. The voltage on V

OCM

Consider the application in Figure 3. V

sets the output

MID

should not exceed 1V below the voltage on V . V

MID OCM

common mode voltage of the 1st differential ampliﬁer

inside the LT6600-2.5 ꢀsee the Block Diagram sectionꢁ 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

resistor and the external 402Ω input resistor. The result-

ing 1.25mA common mode DC current in each input

is a high impedance input.

Table 1. Output Common Range for Various Supplies

SUPPLY

VOLTAGE

DIFFERENTIAL OUT

VOLTAGE SWING

OUTPUT COMMON MODE

RANGE FOR LOW DISTORTION

3V

4V

P-P

2V

P-P

1V

P-P

8V

P-P

4V

P-P

2V

P-P

1V

P-P

9V

P-P

4V

P-P

2V

P-P

1V

P-P

1.4V ≤ V ≤ 1.6V

OCM

1V ≤ V

≤ 1.6V

OCM

+

–

path,must be absorbed by the sources V

OCM

and V

.

0.75V ≤ V

2.4V ≤ V

IN

OCM

V

sets the common mode output voltage of the 2nd

5V

≤ 2.6V

≤ 3.5V

OCM

differential ampliﬁer inside the LT6600-2.5, and therefore

1.5V ≤ V

OCM

sets the common mode output voltage of the ﬁlter. Since,

1V ≤ V

≤ 3.75V

OCM

in the example of Figure 3, V

differs from V by 0.5V,

MID

OCM

0.75V ≤ V

≤ 3.75V

≤ 2V

OCM

an additional 625ꢃA ꢀ312ꢃA per sideꢁ 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.

5V

–2V ≤ V

–3.5V ≤ V

–3.75V ≤ V

–4.25V ≤ V

OCM

≤ 3.5V

≤ 3.75V

NOTE: V

is set by the voltage at this ꢂ . The voltage at V

should

OCM

A simple modiﬁcation to Figure 3 will reduce the DC

OCM

IN

not exceed 1V below the voltage at V . To achieve some of the output

MID

commonmodecurrentsby36ꢅ.IfV isshortedtoV

MID

OCM

common mode ranges shown in the table, the voltage at V

externally to a value below mid supply.

must be set

MID

the common mode output voltage of both op amp stages

will be 2V and the resulting DC current will be 2mA. Of

course,byAC-couplingtheinputsofFigure3,thecommon

mode DC current can be reduced to 625ꢃA.

660025fe

10

LT6600-2.5

APPLICATIONS INFORMATION

Noise

50

40

30

20

10

0

100

80

60

40

20

ThenoiseperformanceoftheLT6600-2.5canbeevaluated

with the circuit of Figure 6.

SPECTꢂAL DENSITY

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.

INTEGꢂATED

2.5V

0

0.01

0.1

1

10

0.1μF

SPECTꢂUM

FꢂEQUENCY ꢀMHzꢁ

COILCꢂAFT

ANALYZEꢂ

660025 F07

ꢂ

3

TTWB-1010

1:1

IN

V

IN

INPUT

1

7

2

8

25ꢄ

–

4

+

Figure 7. Input Referred Noise, Gain = 1

LT6600-2.5

50Ω

–

5

+

0.1μF

Figure 7 is plot of the noise spectral density as a function

6

660025 F06

of frequency for an LT6600-2.5 with ꢂ = 1580Ω using

IN

the ﬁxture of Figure 6 ꢀthe instrument noise has been

–2.5V

subtracted from the resultsꢁ.

Figure 6. (S8 Pin Numbers)

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

noise power added together, the resulting calculated noise

level will be higher than the true differential noise.

Example: With the IC removed and the 25Ω resistors-

grounded,Figure6,measurethetotalintegratednoiseꢀe ꢁ

S

of the spectrum analyzer from 10kHz to 2.5MHz. With the

IC inserted, the signal source ꢀV ꢁ disconnected, and the

IN

inputresistorsgrounded,measurethetotalintegratednoise

out of the ﬁlter ꢀe ꢁ. With the signal source connected, set

O

the frequency to 100kHz and adjust the amplitude until

V measures 100mV . Measure the output amplitude,

IN

P-P

Power Dissipation

V

OUT

, and compute the passband gain A = V /V . Now

OUT IN

TheLT6600-2.5ampliﬁerscombinehighspeedwithlarge-

signal currents in a small package. There is a need to

ensurethatthedie’sjunctiontemperaturedoesnotexceed

150°C. The LT6600-2.5 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" Fꢂ-4 board with 2oz copper, a

totalof 660 square millimeters connected to Pin 6 of the

LT6600-2.5 S8 ꢀ330 square millimeters on each side of

compute the input referred integrated noise ꢀe ꢁ as:

IN

(e_O)²–(e_S)²

e_IN=

A

Table 2 lists the typical input referred integrated noise for

various values of ꢂ .

IN

Table 2. Noise Performance

INPUT REFERRED

INTEGRATED NOISE

10kHz TO 2.5MHz

INPUT REFERRED

INTEGRATED NOISE

10kHz TO 5MHz

PASSBAND

GAIN (V/V)

R

IN

4

2

1

402Ω

806Ω

18ꢃV

29ꢃV

51ꢃV

23ꢃV

39ꢃV

73ꢃV

ꢂMS

the PC boardꢁ will result in a thermal resistance, θ , of

JA

about 85°C/W. Without the extra metal trace connected to

1580Ω

660025fe

11

LT6600-2.5

APPLICATIONS INFORMATION

the V pin to provide a heat sink, the thermal resistance

will be around 105°C/W. Table 3 can be used as a guide

when considering thermal resistance.

–

Foragivensupplyvoltage,theworst-casepowerdissipation

occurs when the differential input signal is maximum, the

common mode currents are maximum ꢀsee Applications

Information regarding Common Mode DC Currentsꢁ, the

load impedance is small and the ambient temperature is

maximum.Tocomputethejunctiontemperature,measure

the supply current under these worst-case conditions, es-

timate the thermal resistance from Table 2, then apply the

Table 3. LT6600-2.5 SO-8 Package Thermal Resistance

COPPER AREA

TOPSIDE BACKSIDE BOARD AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

2

(mm )

1100

330

35

1100

330

35

0

2500

65°C/W

85°C/W

95°C/W

100°C/W

105°C/W

equation for T . For example, using the circuit in Figure 3

J

with DC differential input voltage of 1V, a differential

output voltage of 4V, no load resistance and an ambient

35

+

temperature of 85°C, the supply current ꢀcurrent into V ꢁ

0

measures 37.6mA. Assuming a PC board layout with a

2

Junction temperature, T , is calculated from the ambient-

35mm copper trace, the θ is 100°C/W. The resulting

J

JA

temperature, T , and power dissipation, P . The power

junction temperature is:

A

D

dissipation is the product of supply voltage, V , and

S

T = T + ꢀP • θ ꢁ = 85 + ꢀ5 • 0.0376 • 100ꢁ = 104°C

J

A

D

JA

supply current, I . Therefore, the junction temperature

S

When using higher supply voltages or when driving small

is given by:

impedances, more copper may be necessary to keep T

below 150°C.

J

T = T + ꢀP • θ ꢁ = T + ꢀV • I • θ ꢁ

J

A

D

JA

A

S

JA

wherethesupplycurrent,I ,isafunctionofsignallevel,load

S

impedance, temperature and common mode voltages.

660025fe

12

LT6600-2.5

PACKAGE DESCRIPTION

DF Package

12-Lead Plastic DFN (4mm × 4mm)

ꢀꢂeference LTC DWG # 05-08-1733 ꢂev Øꢁ

2.50 REF

0.70 0.05

3.38 0.05

2.65 0.05

4.50 0.05

3.10 0.05

PACKAGE OUTLINE

0.25 0.05

0.50 BSC

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

4.00 0.10

(4 SIDES)

2.50 REF

7

12

0.40 0.10

3.38 0.10

2.65 0.10

PIN 1 NOTCH

R = 0.20 TYP OR

0.35 × 45°

PIN 1

TOP MARK

(NOTE 6)

CHAMFER

(DF12) DFN 0806 REV Ø

6

R = 0.115

TYP

1

0.25 0.05

0.50 BSC

0.200 REF

0.75 0.05

BOTTOM VIEW—EXPOSED PAD

0.00 – 0.05

NOTE:

1. DRAWING IS PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220

VARIATION (WGGD-X)—TO BE APPROVED

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

660025fe

13

LT6600-2.5

PACKAGE DESCRIPTION

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

ꢀꢂeference LTC DWG # 05-08-1610ꢁ

.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

660025fe

14

LT6600-2.5

REVISION HISTORY ^{(Revision history begins at Rev E)}

REV

DATE

DESCRIPTION

PAGE NUMBER

E

5/10

Updated Order Information section

2

660025fe

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.

15

LT6600-2.5

TYPICAL APPLICATION

5th Order Lowpass Filter (S8 Pin Numbers Shown)

+

V

0.1μF

ꢂ

3

1

–

+

V

–

IN

4

+

–

V

OUT

7

2

+

LT6600

C

V

–

6

8

OUT

5

+

ꢂ

0.1μF

1

C =

2π • ꢂ • 2.5MHz

1580ꢄ

2ꢂ

–

V

GAIN =

, MAXIMUM GAIN = 4

660025 TA02a

Amplitude Response

Transient Response Gain = 1

10

V

= 2.5V

S

GAIN = 1

ꢂ = 787ꢄ

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

V

+

OUT

T

A

= 25°C

50mV/DIV

DIFFEꢂENTIAL

INPUT

200mV/DIV

660025 TA02c

500ns/DIV

100k

1M

10M 20M

FꢂEQUENCY ꢀHzꢁ

660025 TA02b

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Fixed Gain of 1, Matching 0.3ꢅ

Fixed Gain of 2, Matching 0.3ꢅ

Fixed Gain of 5, Matching 0.3ꢅ

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Lowpass Filter

82dB S/N with 3V Supply, SO-8 Package

LT6600-20

Very Low Noise Differential Ampliﬁer and 20MHz

Lowpass Filter

76dB S/N with 3V Supply, SO-8 Package

660025fe

LT 0510 REV E • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

16

●

ꢀ408ꢁ 432-1900 FAX: ꢀ408ꢁ 434-0507 www.linear.com


型号：	LT6600CDF-2.5#PBF
厂家：	Linear
描述：	LT6600-2.5 - Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter; Package: DFN; Pins: 12; Temperature Range: 0°C to 70°C 放大器光电二极管
文件：	总16页 (文件大小：225K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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