Datasheet

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LT6600-2.5

660025fe

TYPICAL APPLICATION

DESCRIPTION

Very Low Noise, Differential

Ampliﬁ er and 2.5MHz Lowpass Filter

The LT

6600-2.5 combines a fully differential ampliﬁ er

with a 4th order 2.5MHz lowpass ﬁ lter approximating a

Chebyshev frequency response. Most differential ampli-

ﬁ ers 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

ﬁ lter’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 ﬁ lter and a differential ampli-

ﬁ er/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

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.

DAC Output Filter

FEATURES

APPLICATIONS

±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 Speciﬁ ed with 3V, 5V, ±5V Supplies

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

RMS

Output

Low Distortion, 1V

RMS

, 800 Load

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

Fully Differential Inputs and Outputs

Compatible with Popular Differential Ampliﬁ er

Pinouts

SO-8 and DFN-12 Packages

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 Ampliﬁ ers

DAC Output Spectrum LT6600-2.5 Output Spectrum

(S8 Pin Numbers Shown)

1580

0.1µF

–5V

0.1µF

–

OUT

–

660025 TA01a

OUT

50MHz

52.3

LADCOM

OUT A

OUT B

CLK

LTC1668

16-BIT 4kHz to 2.5MHz

DISCRETE MULTI-TONE

SIGNAL AT 50MSPS

LT6600-2.5

FREQUENCY (MHz)

(dBm)

–10

–20

–30

–40

–50

–60

–70

–80

–90

0 1201089684726048362412

660025 TA01b

DAC OUTPUT IMAGE

BASEBAND SIGNAL

FREQUENCY (MHz)

(dBm)

–10

–20

–30

–40

–50

–60

–70

–80

–90

0 1201089684726048362412

660025 TA01c

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.

Summary of content (16 pages)

PAGE 1
LT6600-2.5 Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter FEATURES DESCRIPTION n 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 ampliﬁers 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.
PAGE 2
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) ..................
PAGE 3
LT6600-2.5 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 = 1580Ω, and RLOAD = 1k. PARAMETER Filter Gain, VS = 5V RIN = 1580Ω CONDITIONS VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) l VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz) l VIN = 2VP-P, fIN = 12.
PAGE 4
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 (RIN). Note 3: The input common mode voltage is the average of the voltages applied to the external resistors (RIN).
PAGE 5
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 –80 –90 VIN = 2VP-P VS = 3V RL = 800Ω AT EACH OUTPUT –100 –110 1 FREQUENCY (MHz) 0.
PAGE 6
LT6600-2.
PAGE 7
LT6600-2.5 PIN FUNCTIONS (DFN/SO) IN– and IN+ (Pins 1, 12/Pins 1, 8): Input Pins. Signals can be applied to either or both input pins through identical external resistors, RIN. The DC gain from differential inputs to the differential outputs is 1580Ω/RIN. NC (Pins 2, 5, 11/NA): No Connection VOCM (Pin 3/Pin 2): DC Common Mode Reference Voltagefor the 2nd Filter Stage. Its value programs the common mode voltage of the differential output of the ﬁlter.
PAGE 8
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 2VP-P. The common mode output voltage is 1.65V, and the differential output voltage is 2VP-P for frequencies below 2.5MHz. The common mode output voltage is determined by the voltage at VOCM. Since VOCM is shorted to VMID, the output common mode is the mid-supply voltage.
PAGE 9
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 “transimpedance,” is deﬁned as A = VOUT/IIN. To compute the transimpedance, use the following equation: A= 1580 • R1 (Ω) (R1+ R2) By setting R1 + R2 = 1580Ω, the gain equation reduces to A = R1(Ω). The voltage at the pins of the DAC is determined by R1, R2, the voltage on VMID and the DAC output current. Consider Figure 4 with R1 = 49.9Ω and R2 = 1540Ω.
PAGE 10
LT6600-2.5 APPLICATIONS INFORMATION VMID can be allowed to ﬂoat, but it must be bypassed to an AC ground with a 0.01μF capacitor or some instability maybe observed. VMID can be driven from a low impedance 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 VMID. While the internal 11k resistors are well matched, their absolute value can vary by ±20%.
PAGE 11
LT6600-2.5 APPLICATIONS INFORMATION Noise 100 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. 2.5V VIN RIN 1 7 2 8 RIN 3 – + 4 COILCRAFT TTWB-1010 25Ω 1:1 6 5 0.1μF –2.5V Figure 6.
PAGE 12
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. Table 3. LT6600-2.
PAGE 13
LT6600-2.5 PACKAGE DESCRIPTION DF Package 12-Lead Plastic DFN (4mm × 4mm) (Reference LTC DWG # 05-08-1733 Rev Ø) 2.50 REF 0.70 ±0.05 3.38 ±0.05 4.50 ± 0.05 3.10 ± 0.05 2.65 ± 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° CHAMFER PIN 1 TOP MARK (NOTE 6) (DF12) DFN 0806 REV Ø 0.200 REF 6 R = 0.
PAGE 14
LT6600-2.5 PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.355 – 0.
PAGE 15
LT6600-2.5 REVISION HISTORY (Revision history begins at Rev E) REV DATE DESCRIPTION E 5/10 Updated Order Information section PAGE NUMBER 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PAGE 16
LT6600-2.5 TYPICAL APPLICATION 5th Order Lowpass Filter (S8 Pin Numbers Shown) V+ 0.1μF VIN– R R 1 7 C VIN+ C= GAIN = 2 8 R R – 3 + + – 6 VOUT+ VOUT– 5 0.1μF 1 2π • R • 2.5MHz 1580Ω , MAXIMUM GAIN = 4 2R 4 LT6600 V– 660025 TA02a Amplitude Response 10 Transient Response Gain = 1 VS = ±2.