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LTC6405

6405fb

For more information www.linear.com/6405

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Technology Corporation. All other trademarks are the property of their respective owners.

Features

applications

Description

2.7GHz, 5V, Low Noise,

Rail-to-Rail Input Differential

Amplifier/Driver

The LTC

6405 is a very low noise, low distortion, fully

differential input/output amplifier optimized for 5V, single

supply operation. The LTC6405 input common mode range

is rail-to-rail, while the output common mode voltage is

independently adjustable by applying a voltage on the

OCM

pin. This makes the LTC6405 ideal for level shifting

signals with a wide common mode range for driving 12-bit

to 16-bit single supply, differential input ADCs.

A 2.7GHz gain-bandwidth product results in 65dB linearity

for 50MHz input signals. The LTC6405 is unity gain stable

and the closed-loop bandwidth extends from DC to 800MHz.

The output voltage swing extends from near-ground to

4V, to be compatible with a wide range of ADC converter

input requirements. The LTC6405 draws only 18mA, and

has a hardware shutdown feature which reduces current

consumption to 400µA.

The LTC6405 is available in a compact 3mm × 3mm 16-pin

leadless QFN package, as well

as an 8-lead MSOP package,

and operates over a –40°C to 85°C temperature range.

Single-Ended Input to Differential Output

with Common Mode Level Shifting

Low Noise: 1.6nV/√Hz RTI

Low Power: 18mA at 5V

Low Distortion (HD2/HD3):

–82dBc/–65dBc at 50MHz, 2V

P-P

–97dBc/–91dBc at 25MHz, 2V

P-P

Rail-to-Rail Differential Input

4.5V to 5.25V Supply Voltage Range

Fully Differential Input and Output

Adjustable Output Common Mode Voltage

800MHz –3dB Bandwidth with A

= 1

Gain-Bandwidth Product: 2.7GHz

Low Power Shutdown

Available in 8-Lead MSOP and 16-Lead

3mm × 3mm × 0.75mm QFN Packages

Differential Input ADC Driver

Single-Ended to Differential Conversion

Level-Shifting Ground-Referenced Signals

Level-Shifting V

-Referenced Signals

High-Linearity Direct Conversion Receivers

Input Noise Density vs Input

Common Mode Voltage

typical application

–

200Ω

OCM

2.5V

6405 TA01

P-P

200Ω

0.1µF

196Ω

LTC6405UD

0.01µF

1.8pF

50Ω

SIGNAL

GENERATOR

61.9Ω

221Ω

2.5V

P-P

1.8pF

6405 TA01b

2 3.530.5 1 1.5 2.5

0 4.54 5

= 5V

NOISE MEASURED AT f = 1MHz

INPUT VOLTAGE NOISE DENSITY (nV/ Hz)

INPUT CURRENT NOISE DENSITY (pA/ Hz)

INPUT COMMON MODE VOLTAGE (V)

Summary of content (26 pages)

PAGE 1
LTC6405 2.7GHz, 5V, Low Noise, Rail-to-Rail Input Differential Amplifier/Driver Features n n n n n n n n n n n Description Low Noise: 1.6nV/√Hz RTI Low Power: 18mA at 5V Low Distortion (HD2/HD3): –82dBc/–65dBc at 50MHz, 2VP-P –97dBc/–91dBc at 25MHz, 2VP-P Rail-to-Rail Differential Input 4.5V to 5.25V Supply Voltage Range Fully Differential Input and Output Adjustable Output Common Mode Voltage 800MHz –3dB Bandwidth with AV = 1 Gain-Bandwidth Product: 2.
PAGE 2
LTC6405 Absolute Maximum Ratings (Note 1) Total Supply Voltage (V+ to V–).................................5.5V Input Current (+IN, –IN, VOCM, SHDN, V TIP) (Note 2)............. ±10mA Output Short-Circuit Duration (Note 3)............. Indefinite Operating Temperature Range (Note 4)................................................–40°C to 85°C Specified Temperature Range (Note 5) LTC6405I..............................................–40°C to 85°C LTC6405C.................................................
PAGE 3
LTC6405 DC Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = 0V, VCM = VOCM = VICM = 2.5V, VSHDN = open, circuit component values in Figure 1 used, unless otherwise noted. VS is defined as (V+ – V–). VOUTCM is defined as (V+OUT + V–OUT)/2. VICM is defined as (V+IN + V–IN)/2. VOUTDIFF is defined as (V+OUT – V–OUT).
PAGE 4
LTC6405 DC Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = 0V, VCM = VOCM = VICM = 2.5V, VSHDN = open, circuit component values in Figure 1 used, unless otherwise noted. VS is defined as (V+ – V–). VOUTCM is defined as (V+OUT + V–OUT)/2. VICM is defined as (V+IN + V–IN)/2. VOUTDIFF is defined as (V+OUT – V–OUT).
PAGE 5
LTC6405 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: Input pins (+IN, –IN, VOCM, SHDN and VTIP) are protected by steering diodes to either supply. If the inputs should exceed either supply voltage, the input current should be limited to less than 10mA.
PAGE 6
LTC6405 Typical Performance Characteristics Differential Input Referred Offset Voltage vs Input Common Mode Voltage 1.0 1.0 0.4 0.6 0.2 0 0.4 0.2 0 –0.2 –0.2 –0.4 –0.4 –0.6 –0.6 –0.8 –0.8 –1.0 –50 –25 25 50 0 TEMPERATURE (°C) 75 100 –1.0 TA = –40°C TA = 0°C TA = 25°C TA = 70°C TA = 85°C 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 INPUT COMMON MODE VOLTAGE (V) Supply Current vs Supply Voltage 20 VSHDN = OPEN TA = –40°C TA = 0°C TA = 25°C TA = 70°C TA = 85°C 10 5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.
PAGE 7
LTC6405 Typical Performance Characteristics Input Noise Density vs Input Common Mode Voltage 100 10 in 1k 10k 100k FREQUENCY (Hz) 1 10M 1M in 2 2 en 1 1 0 6405 G07 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 INPUT COMMON MODE VOLTAGE (V) 5 VS = 5V RI = RF = 200Ω 10 1 1 10 100 FREQUENCY (MHz) 680 660 640 620 600 –50 0 1000 2000 6405 G10 –25 25 50 0 TEMPERATURE (°C) 100 75 6405 G09 Differential PSRR vs Frequency 90 80 80 70 70 60 60 50 40 0.1 VS = 5V 700 CMRR vs Frequency 100 0.
PAGE 8
LTC6405 Typical Performance Characteristics Small Signal Step Response (QFN Package) Overdriven Output Transient Response Large Signal Step Response 4.5 +OUT VOLTAGE (V) 0.2V/DIV 20mV/DIV 3.5 –OUT 6405 G13 10ns/DIV VS = 5V RLOAD = 400Ω VIN = 2VP-P, DIFFERENTIAL 30 GAIN (dB) 20 10 0 30 AV = 100 AV = 20 20 10 AV = 10 AV = 5 0 AV = 2 AV = 1 –10 –20 –30 VS = 5V –40 VOCM = VICM = 2.5V RLOAD = 400Ω –50 1 10 100 FREQUENCY (MHz) AV (V/V) RI (Ω) 1 2 5 10 20 100 200 200 200 200 200 200 2.5 2.
PAGE 9
LTC6405 Typical Performance Characteristics Harmonic Distortion vs Input Common Mode Voltage Harmonic Distortion vs Frequency –60 –70 HD3 RI = RF = 499Ω –80 HD3 RI = RF = 200Ω –90 –100 –110 HD2 RI = RF = 499Ω 1 –70 –80 –90 HD2 RI = RF = 200Ω 10 FREQUENCY (MHz) RLOAD = 800Ω VS = 5V VOCM = 2.5V VOUTDIFF = 2VP-P –50 VTIP = OPEN (2.8V) DIFFERENTIAL INPUTS fIN = 50MHz RI = RF = 200Ω HD3 –60 –100 100 RI = RF = 499Ω HD2 RI = RF = 499Ω RI = RF = 200Ω 0 0.5 1 1.5 2 2.5 3 3.5 4 4.
PAGE 10
LTC6405 Typical Performance Characteristics Frequency Response vs Load Capacitance Harmonic Distortion vs Input Amplitude Harmonic Distortion vs Frequency –30 CL = 10pF 20 0 CL = 0pF –10 VS = 5V VOCM = VICM = 2.5V = 400Ω R –30 RLOAD I = RF = 300Ω, CF = 1pF CAPACITOR VALUES ARE FROM EACH –40 OUTPUT TO GROUND. NO SERIES RESISTORS ARE USED. –50 1 10 100 1000 2000 FREQUENCY (MHz) –20 DISTORTION (dBc) 10 –40 VS = 5V –40 VOCM = VICM = 2.5V VTIP = OPEN (2.
PAGE 11
LTC6405 pin functions (MSOP/QFN) VOCM (Pin 2/Pin 4): Output Common Mode Reference Voltage. The voltage on VOCM sets the output common mode voltage level (which is defined as the average of the voltages on the +OUT and –OUT pins). The VOCM voltage is internally set by a resistive divider between the supplies, developing a default voltage potential of 2.5V with a 5V supply. The VOCM pin can be over-driven by an external voltage capable of driving the 19kΩ Thevenin equivalent impedance presented by the pin.
PAGE 12
LTC6405 block diagrams LTC6405 Block Diagram/Pinout in MSOP Package 8 +IN 7 6 SHDN 5 V– –OUT V– V+ V+ 37k + 37k – V– V– V+ 1 –IN 2 VOCM 3 V+ 4 +OUT 6405 BD01 LTC6405 Block Diagram/Pinout in QFN Package 16 15 NC 14 +IN –OUT 13 –OUTF 1.25pF SHDN V– 12 1 V+ 2 V– 3 4 V+ V+ V– V+ + 37k V+ V+ 11 V+ V+ 10 1.25pF V+ – 37k 30k VOCM V– 50Ω V– 50Ω V– V– V– 9 38k 1.25pF V– 5 VTIP 6 –IN 7 +OUT 8 +OUTF 6405 BD02 6405fb 12 For more information www.linear.
PAGE 13
LTC6405 applications information Functional Description The LTC6405 is a small outline, wideband, low noise, and low distortion fully-differential amplifier with accurate output phase balancing. The LTC6405 is optimized to drive low voltage, single-supply, differential input analogto-digital converters (ADCs). The LTC6405 input common mode range is rail-to-rail, while the output common mode voltage is independently adjustable by applying a voltage on the VOCM pin.
PAGE 14
LTC6405 Applications Information The outputs (+OUT and –OUT) of the LTC6405 are capable of swinging from close-to-ground to typically 1V below V+. They can source or sink up to approximately 60mA of current. Each output is designed to directly drive up to 5pF to ground. Higher load capacitances should be decoupled with at least 15Ω of series resistance from each output. IC.
PAGE 15
LTC6405 Applications Information General Amplifier Applications ∆b is defined as the difference in feedback factors: As levels of integration have increased and correspondingly, system supply voltages decreased, there has been a need for ADCs to process signals differentially in order to maintain good signal to noise ratios. These ADCs are typically supplied from a single supply voltage which can be as low as 3V, and will have an optimal common mode input range of 1.25V or 1.5V.
PAGE 16
LTC6405 Applications Information In general, the degree of feedback pair mismatch is a source of common mode to differential conversion of both signals and noise. Using 1% resistors or better will mitigate most problems, and will provide about 34dB worst case of common mode rejection. Using 0.1% resistors will provide about 54dB of common mode rejection. A low impedance ground plane should be used as a reference for both the input signal source and the VOCM pin. Bypassing the VOCM with a high quality 0.
PAGE 17
LTC6405 Applications Information Input Common Mode Voltage Range Manipulating the Rail-to-Rail Input Stage with VTIP The LTC6405’s input common mode voltage (VICM) is defined as the average of the two input voltages, V+IN, and V–IN. At the inputs to the actual op amp, the range extends from V– to V+. This makes it easy to interface to a wide range of common mode signals, from ground referenced to VCC referenced signals.
PAGE 18
LTC6405 Applications Information Output Common Mode Voltage Range Output Filter Considerations and Use The output common mode voltage is defined as the average of the two outputs: Filtering at the output of the LTC6405 is often desired to provide anti-aliasing or to improve signal to noise ratio.
PAGE 19
LTC6405 Applications Information tance. The outputs of the LTC6405 are designed to drive 5pF to ground, so care should be taken to not lower the effective impedance between +OUT and +OUTF or –OUT and –OUTF below 15Ω. To decrease filter bandwidth, add two external capacitors, one from +OUTF to ground, and the other from –OUTF to ground.
PAGE 20
LTC6405 Applications Information The LTC6405’s input referred voltage noise contributes the equivalent noise of a 155Ω resistor. When the feedback network is comprised of resistors whose values are less than this, the LTC6405’s output noise is voltage noise dominant (see Figure 11):  R  eno ≈ eni •  1+ F   RI  Feedback networks consisting of resistors with values greater than about 200Ω will result in output noise which is resistor noise and amplifier current noise dominant.
PAGE 21
LTC6405 Applications Information Interfacing the LTC6405 to A/D Converters Rail-to-rail input and fast settling time make the LTC6405 ideal for interfacing to low voltage, single supply, differential input ADCs. The sampling process of ADCs create a sampling glitch caused by switching in the sampling capacitor on the ADC front end which momentarily “shorts” the output of the amplifier as charge is transferred between the amplifier and the sampling capacitor.
PAGE 22
LTC6405 Typical Application Attenuating and Level Shifting a Single-Ended ±5V Signal to a Differential 2VP-P Signal at a 1.25V Common Mode C1, 2.7pF 2VP-P DIFF OUTPUT LEVEL-SHIFTED TO 1.25V R3, 100Ω R5 511Ω ±5V SINE WAVE (10VP-P) CENTERED AT 0V VIN R6 511Ω 5V – + LTC6405 + – 3.3V R1 51.1Ω R2 51.1Ω LTC2207 6405 TA03 R4, 100Ω VCM = 1.25V 2.2µF C2, 2.7pF 6405fb 22 For more information www.linear.
PAGE 23
LTC6405 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev J) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 (.074) 1 1.88 ±0.102 (.074 ±.004) 0.29 REF 1.68 (.066) 0.889 ±0.127 (.035 ±.005) 0.05 REF 5.23 (.206) MIN DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 1.68 ±0.102 3.20 – 3.45 (.
PAGE 24
LTC6405 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691 Rev Ø) 0.70 ±0.05 3.50 ±0.05 1.45 ±0.05 2.10 ±0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ±0.05 15 PIN 1 TOP MARK (NOTE 6) 16 0.40 ±0.
PAGE 25
LTC6405 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION B 02/13 Changed operating voltage upper range from 5.5V to 5.25V PAGE NUMBER Changed voltage max spec from 0.4V to 0.45V 1, 3, 4 3 6405fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 26
LTC6405 Typical Application DC-Coupled Level Shifting of Demodulator Output 5V LT5575 5V 5V C5, 10pF DIFF OUTPUT Z 130Ω| |2.5pF DC LEVEL 1.5V R5, 324Ω 5pF I 65Ω 5pF 65Ω DC LEVEL 3.8V 5V 15nH LTC6405 15nH RF IN 900MHz –7dBm 5V 5V C1 4.7pF 4.7pF 5pF LO OdBm Q 65Ω R7 49.9Ω + – – + C2 4.7pF 3.3V C8 4.7pF R8 49.9Ω R9 10Ω 10dBm C6 R10 4.7pF 10Ω LTC2249 14-BIT ADC VCM C7 4.7pF 5pF 6405 TA02 VOCM = 1.5V 65Ω R6, 324Ω 3.