FEATURES DESCRIPTIO U - Analog Devices · 2020. 2. 1. · 1 LTC1744 1744f 14-Bit, 50Msps ADC Sample...

1

LTC1744

1744f

14-Bit, 50Msps ADC

■ Sample Rate: 50Msps■ 77dB SNR and 87dB SFDR (3.2V Range)■ 73.5dB SNR and 90dB SFDR (2V Range)■ No Missing Codes■ Single 5V Supply■ Power Dissipation: 1.2W■ Selectable Input Ranges: ±1V or ±1.6V■ 150MHz Full Power Bandwidth S/H■ Pin Compatible Family

25Msps: LTC1746 (14 Bit), LTC1745 (12 Bit)50Msps: LTC1744 (14 Bit), LTC1743 (12 Bit)65Msps: LTC1742 (14 Bit), LTC1741 (12 Bit)80Msps: LTC1748 (14 Bit), LTC1747 (12 Bit)

■ 48-Pin TSSOP Package

■ Telecommunications■ Receivers■ Base Stations■ Spectrum Analysis■ Imaging Systems

, LTC and LT are registered trademarks of Linear Technology Corporation.

OF

14-BITPIPELINED ADC

14S/H

CIRCUIT

±1V DIFFERENTIAL

ANALOG INPUT

AIN+

AIN–

SENSE

VCM

4.7µF

DIFF AMP

REFLA REFHB

GND

1744 BD

ENC4.7µF

0.1µF0.1µF1µF 1µF

REFHAREFLB

BUFFER

RANGESELECT

2.5VREF

CORRECTIONLOGIC AND

SHIFTREGISTER

OUTPUTLATCHES

CONTROL LOGIC

OVDD

VDD

OGND

0.5V TO 5V

5V

0.1µF

1µF 1µF 1µF

D13

D0CLKOUT

•••

ENC

DIFFERENTIALENCODE INPUT

OEMSBINV

0.1µF

The LTC®1744 is a 50Msps, sampling 14-bit A/D con-verter designed for digitizing high frequency, wide dynamicrange signals. Pin selectable input ranges of ±1V and ±1.6Valong with a resistor programmable mode allow theLTC1744’s input range to be optimized for a wide varietyof applications.

The LTC1744 is perfect for demanding communicationsapplications with AC performance that includes 77dBSNR and 87dB spurious free dynamic range. Ultralow jitterof 0.3psRMS allows undersampling of IF frequencies withexcellent noise performance. DC specs include ±4LSBmaximum INL and no missing codes over temperature.

The digital interface is compatible with 5V, 3V and 2V logicsystems. The ENC and ENC inputs may be driven differen-tially from PECL, GTL and other low swing logic families orfrom single-ended TTL or CMOS. The low noise, high gainENC and ENC inputs may also be driven by a sinusoidalsignal without degrading performance. A separate outputpower supply can be operated from 0.5V to 5V, making iteasy to connect directly to any low voltage DSPs or FIFOs.

The TSSOP package with a flow-through pinout simplifiesthe board layout.

50Msps, 14-Bit ADC with a ±1V Differential Input Range

DESCRIPTIO

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FEATURES

APPLICATIO SU

BLOCK DIAGRA

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2

LTC1744

1744f

PARAMETER CONDITIONS MIN TYP MAX UNITS

Resolution (No Missing Codes) ● 14 Bits

Integral Linearity Error (Note 6) ● – 4 ±1 4 LSBDifferential Linearity Error ● –1 ±0.5 1.5 LSBOffset Error (Note 7) – 20 ±5 20 mVGain Error External Reference (SENSE = 1.6V) –3 ±1 3 %FSFull-Scale Tempco IOUT(REF) = 0 ±40 ppm/°C

ORDER PARTNUMBER

OVDD = VDD (Notes 1, 2)Supply Voltage (VDD) ................................................ 6VAnalog Input Voltage (Note 3) .... –0.3V to (VDD + 0.3V)Digital Input Voltage (Note 4) ..... –0.3V to (VDD + 0.3V)Digital Output Voltage ................. –0.3V to (VDD + 0.3V)OGND Voltage ..............................................–0.3V to 1VPower Dissipation ............................................ 2000mWOperating Temperature Range

LTC1744C ............................................... 0°C to 70°CLTC1744I ............................................ – 40°C to 85°C

Storage Temperature Range ................. –65°C to 150°CLead Temperature (Soldering, 10 sec).................. 300°C

LTC1744CFWLTC1744IFW

TJMAX = 150°C, θJA = 35°C/W

Consult factory for parts specified with wider operating temperature ranges.

The ● indicates specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. (Note 5)

ABSOLUTE MAXIMUM RATINGS

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PACKAGE/ORDER INFORMATION

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123456789

101112131415161718192021222324

TOP VIEW

FW PACKAGE48-LEAD PLASTIC TSSOP

484746454443424140393837363534333231302928272625

SENSEVCMGNDAIN

+

AIN–

GNDVDDVDDGND

REFLBREFHA

GNDGND

REFLAREFHB

GNDVDDVDDGNDVDDGND

MSBINVENCENC

OFOGNDD13D12D11OVDDD10 D9D8D7OGNDGNDGNDD6D5D4OVDDD3D2D1D0OGNDCLKOUTOE

CO VERTER CHARACTERISTICS

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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN Analog Input Range (Note 8) 4.75V ≤ VDD ≤ 5.25V ● ±1 to ±1.6 VIIN Analog Input Leakage Current 10 nA

CIN Analog Input Capacitance Sample Mode ENC < ENC 15 pFHold Mode ENC > ENC 8 pF

tACQ Sample-and-Hold Acquisition Time ● 7.5 9.5 ns

tAP Sample-and-Hold Acquisition Delay Time 0 ns

tJITTER Sample-and-Hold Acquisition Delay Time Jitter 0.3 psRMSCMRR Analog Input Common Mode Rejection Ratio 1.0V < (AIN– = AIN+) < 3.5V 80 dB

The ● indicates specifications which apply over the full operating temperature range, otherwisespecifications are at TA = 25°C. (Note 5)A ALOG I PUT

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LTC1744

1744f


SNR Signal-to-Noise Ratio 5MHz Input Signal (2V Range) 73.5 dBFS5MHz Input Signal (3.2V Range) ● 75.5 77 dBFS

25MHz Input Signal (2V Range) 72.5 dBFS25MHz Input Signal (3.2V Range) 75.5 dBFS

70MHz Input Signal (2V Range) 70 dBFS70MHz Input Signal (3.2V Range) 71.5 dBFS

SFDR Spurious Free Dynamic Range 5MHz Input Signal (2V Range) 92 dB5MHz Input Signal (3.2V Range) ● 76 87 dB

25MHz Input Signal (2V Range) 87 dB25MHz Input Signal (3.2V Range) 79 dB

70MHz Input Signal (2V Range) 73 dB70MHz Input Signal (3.2V Range) 66 dB

S/(N + D) Signal-to-(Noise + Distortion) Ratio 5MHz Input Signal (2V Range) 73 dBFS5MHz Input Signal (3.2V Range) ● 73 76 dBFS

25MHz Input Signal (2V Range) 72.5 dBFS25MHz Input Signal (3.2V Range) 73.5 dBFS

70MHz Input Signal (2V Range) 68 dBFS70MHz Input Signal (3.2V Range) 64 dBFS

THD Total Harmonic Distortion 5MHz Input Signal, First 5 Harmonics (2V Range) – 90 dB5MHz Input Signal, First 5 Harmonics (3.2V Range) – 85 dB

25MHz Input Signal, First 5 Harmonics (2V Range) – 85 dB25MHz Input Signal, First 5 Harmonics (3.2V Range) – 78 dB

70MHz Input Signal, First 5 Harmonics (2V Range) – 72 dB70MHz Input Signal, First 5 Harmonics (3.2V Range) – 65 dB

IMD Intermodulation Distortion fIN1 = 2.52MHz, fIN2 = 5.2MHz (2V Range) – 90 dBcfIN1 = 2.52MHz, fIN2 = 5.2MHz (3.2V Range) – 80 dBc

Sample-and-Hold Bandwidth RSOURCE = 50Ω 150 MHz

PARAMETER CONDITIONS MIN TYP MAX UNITS

VCM Output Voltage IOUT = 0 2.42 2.5 2.58 V

VCM Output Tempco IOUT = 0 ±30 ppm/°CVCM Line Regulation 4.75V ≤ VDD ≤ 5.25V 3 mV/VVCM Output Resistance 1mA ≤ IOUT ≤ 1mA 4 Ω

The ● indicates specifications which apply over the full operating temperature range,otherwise specifications are at TA = 25°C. AIN = –1dBFS. (Note 5)DY A IC ACCURACY

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(Note 5)I TER AL REFERE CE CHARACTERISTICSU U U

4

LTC1744

1744f

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITSfSAMPLE(MAX) Maximum Sampling Frequency ● 50 MHzt1 ENC Low Time (Note 9) ● 9.5 10 1000 nst2 ENC High Time (Note 9) ● 9.5 10 1000 nst3 Aperture Delay of Sample-and-Hold 0 nst4 ENC to Data Delay CL = 10pF (Note 8) ● 1.4 4.5 8 nst5 ENC to CLKOUT Delay CL = 10pF (Note 8) ● 0.5 2.3 5 nst6 CLKOUT to Data Delay CL = 10pF (Note 8) ● 0 2.2 nst7 DATA Access Time After OE ↓ CL = 10pF (Note 8) 10 25 nst8 BUS Relinquish Time (Note 8) 10 25 ns

Data Latency 5 cycles

The ● indicates specifications which apply over the full operating temperaturerange, otherwise specifications are at TA = 25°C. (Note 5)TI I G CHARACTERISTICS

UW

Note 1: Absolute Maximum Ratings are those values beyond which the lifeof a device may be impaired.Note 2: All voltage values are with respect to ground with GND(unless otherwise noted).Note 3: When these pin voltages are taken below GND or above VDD, theywill be clamped by internal diodes. This product can handle input currentsof greater than 100mA below GND or above VDD without latchup.Note 4: When these pin voltages are taken below GND, they will beclamped by internal diodes. This product can handle input currents of>100mA below GND without latchup. These pins are not clamped to VDD.

Note 5: VDD = 5V, fSAMPLE = 50MHz, differential ENC/ENC = 2VP-P 50MHzsine wave, input range = ±1.6V differential, unless otherwise specified.Note 6: Integral nonlinearity is defined as the deviation of a code from astraight line passing through the actual endpoints of the transfer curve.The deviation is measured from the center of the quantization band.Note 7: Bipolar offset is the offset voltage measured from – 0.5 LSBwhen the output code flickers between 00 0000 0000 0000 and 111111 1111 1111.Note 8: Guaranteed by design, not subject to test.Note 9: Recommended operating conditions.


VDD Positive Supply Voltage 4.75 5.25 V

IDD Positive Supply Current ● 245 300 mA

PDIS Power Dissipation ● 1.2 1.5 W

OVDD Digital Output Supply Voltage 0.5 VDD V

The ● indicates specifications which apply over the full operating temperaturerange, otherwise specifications are at TA = 25°C. (Note 5)POWER REQUIRE E TS

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VIH High Level Input Voltage VDD = 5.25V ● 2.4 V

VIL Low Level Input Voltage VDD = 4.75V ● 0.8 V

IIN Digital Input Current VIN = 0V to VDD ● ±10 µACIN Digital Input Capacitance MSBINV and OE Only 1.5 pF

VOH High Level Output Voltage OVDD = 4.75V IO = –10µA 4.74 V

IO = –200µA ● 4 VVOL Low Level Output Voltage OVDD = 4.75V IO = 160µA 0.05 V

IO = 1.6mA ● 0.1 0.4 V

IOZ Hi-Z Output Leakage D13 to D0 VOUT = 0V to VDD, OE = High ● ±10 µACOZ Hi-Z Output Capacitance D13 to D0 OE = High (Note 8) ● 15 pF

ISOURCE Output Source Current VOUT = 0V – 50 mA

ISINK Output Sink Current VOUT = 5V 50 mA

The ● indicates specifications which apply over the fulloperating temperature range, otherwise specifications are at TA = 25°C. (Note 5)DIGITAL I PUTS A D DIGITAL OUTPUTS

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5

LTC1744

1744f

TYPICAL PERFOR A CE CHARACTERISTICS

UW

CODE0 4000 8000 12000 16000

INL

ERRO

R (L

SB)

1744 G01

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

TA = 25°C

CODE0 4000 8000 12000 16000

DNL

ERRO

R (L

SB)

1744 G02

1.0

0.8

0.6

0.4

0.2

0

–0.2

–0.4

–0.6

–0.8

–1.0

TA = 25°C

FREQUENCY (MHz)0

25.37

AMPL

ITUD

E (d

BFS)

1744 G03

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.02 4 6 8 10 12 14 16 18 20 22 24

TA = 25°C

Typical INL, 3.2V Range Typical DNL, 3.2V Range

Nonaveraged, 8192 Point FFT,Input Frequency = 2.5MHz, –1dB,2V Range

Nonaveraged, 8192 Point FFT,Input Frequency = 20MHz, –1dB,2V Range

Nonaveraged, 8192 Point FFT,Input Frequency = 2.5MHz, –1dB,3.2V Range

Nonaveraged, 8192 Point FFT,Input Frequency = 20MHz, –1dB,3.2V Range

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G04

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G05

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G06

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

Averaged, 8192 Point 2-Tone FFT,Input Frequency = 2.5MHz and5.2MHz, 2V Range

Averaged, 8192 Point 2-Tone FFT,Input Frequency = 2.5MHz and5.2MHz, 3.2V Range

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G07

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G08

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

(Note 5)

Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –6dB,2V Range

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G10

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

6

LTC1744

1744f


UW

Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –20dB,3.2V Range

Averaged, 8192 Point FFT, InputFrequency = 20MHz, –6dB,2V Range

Averaged, 8192 Point FFT, InputFrequency = 20MHz, –6dB,3.2V Range

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G13

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G14

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G15

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C


Averaged, 8192 Point FFT, InputFrequency = 20MHz, –20dB,3.2V Range


FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G16

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G17

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G18

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –6dB,3.2V Range

Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –20dB,2V Range

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G11

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G12

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

(Note 5)


FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G19

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

7

LTC1744

1744f


UW


Averaged, 8192 Point FFT, InputFrequency = 70MHz, – 1dB,2V Range

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G20

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G21

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0



SNR vs Sample Rate, InputFrequency = 5MHz, –1dB

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G22

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

TA = 25°C

FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24

25.37

AMPL

ITUD

E (d

BFS)

1744 G23

0.5

–10.0

–20.0

–30.0

–40.0

–50.0

–60.0

–70.0

–80.0

–90.0

–100.0

–110.0

–120.0

SAMPLE RATE (Msps)0 20 40 60 80 100

SNR

(dBF

S)

1744 G24

78

77

76

75

74

73

72

71

70

69

68

2V RANGE

3.2V RANGE

TA = 25°C

SFDR vs Sample Rate, InputFrequency = 5MHz, –1dB

SAMPLE RATE (Msps)0 20 40 60 80 100

SFDR

(dBc

)

1744 G25

100

95

90

85

80

75

70

65

60

55

50

2V RANGE

3.2V RANGE

TA = 25°C

(Note 5)

Grounded Input Histogram

CODE8152 8153 8154 8155 8156 8157 8158

COUN

T

1744 G09

40000

35000

30000

25000

20000

15000

10000

5000

0

TA = 25°C

SNR vs Input Frequency andAmplitude, 3.2V Range

INPUT FREQUENCY (MHz)1

SNR

(dBc

)

80

75

70

65

60

55

5010 100

1744 G31

–1dBFS

–6dBFS

–20dBFS

TA = 25°C


SNR

(dBc

)

75

70

65

60

55

5010 100

1744 G30

–1dBFS

–6dBFS

–20dBFS

TA = 25°C

TA = 25°C

SNR vs Input Frequency andAmplitude, 2V Range

8

LTC1744

1744f


UW

(Note 5)

SAMPLE RATE (Msps)0

POW

ER (m

W)

1050

1075

1100

30 50

1744 G35

1025

1000

97510 20 40

1125

1150

1175TA = 25°C

Power Dissipation vs Sample Rate

SFDR vs Input Frequency andAmplitude, 2V Range

SFDR vs Input Frequency andAmplitude, 3.2V Range


SFDR

(dBF

S)

120

110

100

90

80

70

6010 100

1744 G32

–1dBFS

–6dBFS

–20dBFSTA = 25°C


SFDR

(dBF

S)

120

110

100

90

80

70

6010 100

1744 G33

–1dBFS

–6dBFS

–20dBFSTA = 25°C


AMPL

ITUD

E (d

Bc)

–60

–70

–80

–90

–100

–110

–12010 100

1744 G29

TA = 25°C

Worst Harmonic 4th or Higher vsInput Frequency, 3.2V Range, –1dB


AMPL

ITUD

E (d

Bc)

–60

–70

–80

–90

–100

–11010 100

1744 G28

3rd HARMONIC

2nd HARMONIC

TA = 25°C

2nd and 3rd Harmonic vs InputFrequency, 3.2V Range, –1dB

2nd and 3rd Harmonic vs InputFrequency, 2V Range, –1dB

Worst Harmonic 4th or Higher vsInput Frequency, 2V Range, –1dB


AMPL

ITUD

E (d

Bc)

–60

–70

–80

–90

–100

–11010 100

1744 G26

3rd HARMONIC

2nd HARMONIC

TA = 25°C


AMPL

ITUD

E (d

Bc)

–60

–70

–80

–90

–100

–11010 100

1744 G27

TA = 25°C

INPUT AMPLITUDE (dBFS)

SFDR

(dBc

AND

dBF

S)

110

100

90

80

70

60

50

40

1744 G34

–60 –40 –20 0

SFDR dBFS

SFDR dBc

TA = 25°C

SFDR vs Input Amplitude, 2VRange, 5MHz Input Frequency

9

LTC1744

1744f

SENSE (Pin 1): Reference Sense Pin. Ground selects±1V. VDD selects ±1.6V. Greater than 1V and less than1.6V applied to the SENSE pin selects an input range of±VSENSE, ±1.6V is the largest valid input range.VCM (Pin 2): 2.5V Output and Input Common Mode Bias.Bypass to ground with 4.7µF ceramic chip capacitor.GND (Pins 3, 6, 9, 12, 13, 16, 19, 21, 36, 37): ADCPower Ground.AIN+ (Pin 4): Positive Differential Analog Input.AIN– (Pin 5): Negative Differential Analog Input.VDD (Pins 7, 8, 17, 18, 20): 5V Supply. Bypass to AGNDwith 1µF ceramic chip capacitor.REFLB (Pin 10): ADC Low Reference. Bypass to Pin 11 with0.1µF ceramic chip capacitor. Do not connect to Pin␣ 14.REFHA (Pin 11): ADC High Reference. Bypass to Pin 10 with0.1µF ceramic chip capacitor, to Pin 14 with a 4.7µF ceramiccapacitor and to ground with 1µF ceramic capacitor.REFLA (Pin 14): ADC Low Reference. Bypass to Pin 15 with0.1µF ceramic chip capacitor, to Pin 11 with a 4.7µF ceramiccapacitor and to ground with 1µF ceramic capacitor.REFHB (Pin 15): ADC High Reference. Bypass to Pin 14 with0.1µF ceramic chip capacitor. Do not connect to Pin␣ 11.

PI FU CTIO S

UUU

MSBINV (Pin 22): MSB Inversion Control. Low invertsthe MSB, 2’s complement output format. High does notinvert the MSB, offset binary output format.ENC (Pin 23): Encode Input. The input sample starts onthe positive edge.ENC (Pin 24): Encode Complement Input. Conversionstarts on the negative edge. Bypass to ground with 0.1µFceramic for single-ended encode signal.OE (Pin 25): Output Enable. Low enables outputs. Logichigh makes outputs Hi-Z.CLKOUT (Pin 26): Data Valid Output. Latch data on therising edge of CLKOUT.OGND (Pins 27, 38, 47): Output Driver Ground.D0-D3 (Pins 28 to 31): Digital Outputs. D0 is the LSB.OVDD (Pins 32, 43): Positive Supply for the Output Driv-ers. Bypass to ground with 0.1µF ceramic chip capacitor.D4-D6 (Pins 33 to 35): Digital Outputs.D7-D10 (Pins 39 to 42): Digital Outputs.D11-D13 (Pins 44 to 46): Digital Outputs. D13 is the MSB.OF (Pin 48): Over/Under Flow Output. High when an overor under flow has occurred.


UW

(Note 5)

FREQUENCY (MHz)0

AMPL

ITUD

E (d

B)

–60

–30

0.5–10–20

–40–50

–70–80

–100–110

–130–140

8 1624.99

1744 G36

–90

–120

–1502 4 6 10 12 14 18 20 22 24

TA = 25°C

FREQUENCY (MHz)0

AMPL

ITUD

E (d

B)

–60

–30

0.5–10–20

–40–50

–70–80

–100–110

–130–140

8 1624.99

1744 G37

–90

–120

–1502 4 6 10 12 14 18 20 22 24

TA = 25°C

Input = 5MHz, –25dBFS, No DitherInput = 5MHz, –25dBFS,Dither Applied

10

LTC1744

1744f

OF

14-BITPIPELINED ADC

14S/H

CIRCUIT

±1V DIFFERENTIAL

ANALOG INPUT

AIN+

AIN–

SENSE

VCM

4.7µF

DIFF AMP

REFLA REFHB

GND

1744 BD

ENC4.7µF

0.1µF0.1µF1µF 1µF

REFHAREFLB

BUFFER

RANGESELECT

2.5VREF

CORRECTIONLOGIC AND

SHIFTREGISTER

OUTPUTLATCHES

CONTROL LOGIC

OVDD

VDD

OGND

0.5V TO 5V

5V

0.1µF

1µF 1µF 1µF

D13

D0CLKOUT

•••

ENC

DIFFERENTIALENCODE INPUT

OEMSBINV

0.1µF

t4

1744 TD

t3

t6

t5 t5

N

t1t2

DATA (N – 5)DB13 TO DB0

ANALOGINPUT

ENCODE

DATA

CLKOUT



t7 t8

DATA NDB13 TO DB0, OF AND CLKOUT

OE

DATA

TI I G DIAGRAUW W

UU WFU CTIO AL BLOCK DIAGRA

11

LTC1744

1744f

APPLICATIO S I FOR ATIO

WU UU

2, 3, etc. The 3rd order intermodulation products are 2fa+ fb, 2fb + fa, 2fa – fb and 2fb – fa. The intermodulationdistortion is defined as the ratio of the RMS value of eitherinput tone to the RMS value of the largest 3rd orderintermodulation product.

Spurious Free Dynamic Range (SFDR)

Spurious free dynamic range is the peak harmonic orspurious noise that is the largest spectral componentexcluding the input signal and DC. This value is expressedin decibels relative to the RMS value of a full scale inputsignal.

Input Bandwidth

The input bandwidth is that input frequency at which theamplitude of the reconstructed fundamental is reduced by3dB for a full scale input signal.

Aperture Delay Time

The time from when a rising ENC equals the ENC voltageto the instant that the input signal is held by the sample andhold circuit.

Aperture Delay Jitter

The variation in the aperture delay time from conversion toconversion. This random variation will result in noisewhen sampling an AC input. The signal to noise ratio dueto the jitter alone will be:

SNRJITTER = –20log (2π) • FIN • TJITTER

CONVERTER OPERATION

As shown in Figure 1, the LTC1744 is a CMOS pipelinedmultistep converter. The converter has four pipelinedADC stages; a sampled analog input will result in adigitized value five cycles later, see the Timing Diagramsection. The analog input is differential for improvedcommon mode noise immunity and to maximize the inputrange. Additionally, the differential input drive will reduceeven order harmonics of the sample-and-hold circuit. Theencode input is also differential for improved commonmode noise immunity.

DYNAMIC PERFORMANCE

Signal-to-Noise Plus Distortion Ratio

The signal-to-noise plus distortion ratio [S / (N + D)] is theratio between the RMS amplitude of the fundamental inputfrequency and the RMS amplitude of all other frequencycomponents at the ADC output. The output is band limitedto frequencies above DC to below half the samplingfrequency.

Signal-to-Noise Ratio

The signal-to-noise ratio (SNR) is the ratio between theRMS amplitude of the fundamental input frequency andthe RMS amplitude of all other frequency componentsexcept the first five harmonics and DC.

Total Harmonic Distortion

Total harmonic distortion is the ratio of the RMS sum of allharmonics of the input signal to the fundamental itself. Theout-of-band harmonics alias into the frequency bandbetween DC and half the sampling frequency. THD isexpressed as:

THD LogV V V Vn

V= + + +20 2 3 4

1

2 2 2 2...

where V1 is the RMS amplitude of the fundamental fre-quency and V2 through Vn are the amplitudes of thesecond through nth harmonics. The THD calculated in thisdata sheet uses all the harmonics up to the fifth.

Intermodulation Distortion

If the ADC input signal consists of more than one spectralcomponent, the ADC transfer function nonlinearity canproduce intermodulation distortion (IMD) in addition toTHD. IMD is the change in one sinusoidal input caused bythe presence of another sinusoidal input at a differentfrequency.

If two pure sine waves of frequencies fa and fb are appliedto the ADC input, nonlinearities in the ADC transferfunction can create distortion products at the sum anddifference frequencies of mfa ± nfb, where m and n = 0, 1,

12

LTC1744

1744f


WU UUFigure 1. Block Diagram

DIFFREFAMP

REFBUF

4.7µF

1µF0.1µF 0.1µF

1µF

INTERNAL CLOCK SIGNALSREFL REFH

DIFFERENTIALINPUT

LOW JITTERCLOCKDRIVER

RANGESELECT

2.5VREFERENCE

5-BITPIPELINEDADC STAGE

FIRST STAGE


SECOND STAGE


THIRD STAGE

4-BITFLASHADC

FOURTH STAGE

ENCREFHAREFLB REFLA REFHB ENC

SHIFT REGISTERAND CORRECTION

OEMSBINV OGND

OF

OVDD 0.5V TO5V

D13

D0

CLKOUT

1744 F01

INPUTS/H

SENSE

VCM

AIN–

AIN+

4.7µF

OUTPUTDRIVERS

CONTROL LOGICAND

CALIBRATION LOGIC

•••

The LTC1744 has two phases of operation, determined bythe state of the differential ENC/ENC input pins. For brev-ity, the text will refer to ENC greater than ENC as ENC highand ENC less than ENC as ENC low.

Each pipelined stage shown in Figure 1 contains an ADC,a reconstruction DAC and an interstage residue amplifier.In operation, the ADC quantizes the input to the stage andthe quantized value is subtracted from the input by theDAC to produce a residue. The residue is amplified andoutput by the residue amplifier. Successive stages operateout of phase so that when the odd stages are outputtingtheir residue, the even stages are acquiring that residueand visa versa.

When ENC is low, the analog input is sampled differentiallydirectly onto the input sample-and-hold capacitors, insidethe “Input S/H” shown in the block diagram. At the instantthat ENC transitions from low to high, the sampled inputis held. While ENC is high, the held input voltage isbuffered by the S/H amplifier which drives the first pipelinedADC stage. The first stage acquires the output of the S/Hduring this high phase of ENC. When ENC goes back low,

the first stage produces its residue which is acquired bythe second stage. At the same time, the input S/H goesback to acquiring the analog input. When ENC goes backhigh, the second stage produces its residue which isacquired by the third stage. An identical process is re-peated for the third stage, resulting in a third stage residuethat is sent to the fourth stage ADC for final evaluation.

Each ADC stage following the first has additional range toaccommodate flash and amplifier offset errors. Resultsfrom all of the ADC stages are digitally delayed such thatthe results can be properly combined in the correctionlogic before being sent to the output buffer.

SAMPLE/HOLD OPERATION AND INPUT DRIVE

Sample Hold Operation

Figure 2 shows an equivalent circuit for the LTC1744CMOS differential sample-and-hold. The differential ana-log inputs are sampled directly onto sampling capacitors(CSAMPLE) through CMOS transmission gates. This directcapacitor sampling results in lowest possible noise for a

13

LTC1744

1744f


WU UU

given sampling capacitor size. The capacitors shownattached to each input (CPARASITIC) are the summation ofall other capacitance associated with each input.

During the sample phase when ENC/ENC is low, thetransmission gate connects the analog inputs to the sam-pling capacitors and they charge to and track the differen-tial input voltage. When ENC/ENC transitions from low tohigh the sampled input voltage is held on the samplingcapacitors. During the hold phase when ENC/ENC is highthe sampling capacitors are disconnected from the inputand the held voltage is passed to the ADC core forprocessing. As ENC/ENC transitions from high to low theinputs are reconnected to the sampling capacitors toacquire a new sample. Since the sampling capacitors stillhold the previous sample, a charging glitch proportional to

the change in voltage between samples will be seen at thistime. If the change between the last sample and the newsample is small the charging glitch seen at the input will besmall. If the input change is large, such as the change seenwith input frequencies near Nyquist, then a larger chargingglitch will be seen.

Common Mode Bias

The ADC sample-and-hold circuit requires differentialdrive to achieve specified performance. Each input shouldswing ±0.8V for the 3.2V range or ±0.5V for the 2V range,around a common mode voltage of 2.5V. The VCM outputpin (Pin 2) may be used to provide the common mode biaslevel. VCM can be tied directly to the center tap of atransformer to set the DC input level or as a reference levelto an op amp differential driver circuit. The VCM pin mustbe bypassed to ground close to the ADC with 4.7µF orgreater.

Input Drive Impedance

As with all high performance, high speed ADCs the dy-namic performance of the LTC1744 can be influenced bythe input drive circuitry, particularly the second and thirdharmonics. Source impedance and input reactance caninfluence SFDR. At the falling edge of encode the sample-and-hold circuit will connect the 7pF sampling capacitor tothe input pin and start the sampling period. The samplingperiod ends when encode rises, holding the sampled inputon the sampling capacitor. Ideally the input circuitryshould be fast enough to fully charge the sampling capaci-tor during the sampling period 1/(2FENCODE); however,this is not always possible and the incomplete settling maydegrade the SFDR. The sampling glitch has been designedto be as linear as possible to minimize the effects ofincomplete settling.

For the best performance, it is recomended to have asource impedence of 100Ω or less for each input. Thesource impedence should be matched for the differentialinputs. Poor matching will result in higher even orderharmonics, especially the second.

Figure 2. Equivalent Input Circuit

CSAMPLE7pF

CPARASITIC8pF

CPARASITIC8pF

VDD

LTC1744

AIN+

1744 F02

CSAMPLE7pF

BIAS

VDD

5V

AIN–

ENC

ENC

2V

6k

2V

6k

14

LTC1744

1744f


WU UU

Input Drive Circuits

Figure 3 shows the LTC1744 being driven by an RFtransformer with a center tapped secondary. The second-ary center tap is DC biased with VCM, setting the ADC inputsignal at its optimum DC level. Figure 3 shows a 1:1 turnsratio transformer. Other turns ratios can be used if thesource impedence seen by the ADC does not exceed 100Ωfor each ADC input. A disadvantage of using a transformeris the loss of low frequency response. Most small RFtransformers have poor performance at frequencies be-low 1MHz.

frequencies higher than 40MHz, the capacitors may needto be decreased to prevent excessive signal loss.

Reference Operation

Figure 5 shows the LTC1744 reference circuitry consistingof a 2.5V bandgap reference, a difference amplifier andswitching and control circuit. The internal voltage refer-ence can be configured for two pin selectable input rangesof 2V(±1V differential) or 3.2V(±1.6V differential). Tyingthe SENSE pin to ground selects the 2V range; tying theSENSE pin to VDD selects the 3.2V range.

The 2.5V bandgap reference serves two functions: itsoutput provides a DC bias point for setting the commonmode voltage of any external input circuitry; additionally,the reference is used with a difference amplifier to gener-ate the differential reference levels needed by the internalADC circuitry.

1:1 37Ω0.1µF

ANALOGINPUT

VCM

AIN+

AIN–

100Ω 100Ω 18pF

18pF

18pF

1744 F03

4.7µF

37Ω

LTC1744

37Ω

5V

SINGLE-ENDEDINPUT

2.5V ±1/2 RANGE

VCM

AIN+

AIN–

18pF

18pF

18pF

1744 F04a

4.7µF

37Ω

100Ω

500Ω 500Ω

LTC1744

–

+1/2 LT1810

–

+1/2 LT1810

Figure 3. Single-Ended to DifferentialConversion Using a Transformer

Figure 4a. Differential Drive with Op Amps

Figure 4b. Using the LT6600 as a Differential Driver

5V

14

3

GAIN = 402Ω/RINMAXIMUM GAIN = 4

56

2

78

VCM

AIN+

AIN–

18pF

1744 F04b

1µF

49.9Ω

49.9Ω

RIN402Ω

RIN402Ω

0.1µF

0.01µF

LTC1744–

+

–+

LT6600-20VOCM

VMIDVIN

Figure 4a demonstrates the use of operational amplifiersto convert a single ended input signal into a differentialinput signal. The advantage of this method is that itprovides low frequency input response; however, thelimited gain bandwidth of most op amps will limit theSFDR at high input frequencies.

Figure 4b shows the LT6600, a low noise differentialamplifier and lowpass filter, used as an input driver. TheLT6600 provides two functions: it serves as a 4th orderlowpass filter and as a single-ended to differential con-verter. Additionally it can be programmed with one exter-nal resistor to provide a gain from 1 to 4. Three versionsof this device are available having lowpass filter band-widths of 2.5MHz, 10MHz or 20MHz.

The 37Ω resistors and 18pF capacitors on the analoginputs serve two purposes: isolating the drive circuitryfrom the sample-and-hold charging glitches and limitingthe wideband noise at the converter input. For input

15

LTC1744

1744f


WU UU

An external bypass capacitor of 4.7µF or larger is requiredfor the 2.5V reference output, VCM. This provides a highfrequency low impedance path to ground for internal andexternal circuitry. This is also the compensation capacitorfor the reference. It will not be stable without this capacitor.

The difference amplifier generates the high and low refer-ence for the ADC. High speed switching circuits areconnected to these outputs and they must be externallybypassed. Each output has two pins: REFHA and REFHBfor the high reference and REFLA and REFLB for the lowreference. The doubled output pins are needed to reducepackage inductance. Bypass capacitors must be con-nected as shown in Figure 5.

VCM

REFHA

REFLB

SENSETIE TO VDD FOR 3.2V RANGE;

TIE TO GND FOR 2V RANGE;RANGE = 2 • VSENSE FOR

1V < VSENSE < 1.6V

2.5V

REFLA

REFHB

4.7µF

4.7µF

INTERNAL ADCHIGH REFERENCE

BUFFER

0.1µF

1744 F05

LTC1744

4Ω

DIFF AMP

1µF

1µF 0.1µF

INTERNAL ADCLOW REFERENCE

2.5V BANDGAPREFERENCE

1.6V 1V

RANGEDETECT

ANDCONTROL

Figure 5. Equivalent Reference Circuit

VCM

SENSE

2.5V

1.1V

4.7µF14k

1µF11k

1744 F06a

LTC1744

VCM

SENSE

2.5V

5V1.25V64

1, 2

4.7µF

1µF0.1µF

1744 F06b

LTC1744LT1790-1.25

Figure 6a. 2.2V Range ADC Figure 6b. 2.5V Range ADC with an External Reference

Other voltage ranges in between the pin selectable rangescan be programmed with two external resistors as shownin Figure 6a. An external reference can be used by applyingits output directly or through a resistor divider to SENSE.It is not recommended to drive the SENSE pin with a logicdevice since the logic threshold is close to ground andVDD. The SENSE pin should be tied high or low as close tothe converter as possible. If the SENSE pin is drivenexternally, it should be bypassed to ground as close to thedevice as possible with a 1µF ceramic capacitor.

16

LTC1744

1744f

Input Range

The input range can be set based on the application. Foroversampled signal processing in which the input fre-quency is low (10MHz), the 2V range will have the best SFDR perfor-mance but the SNR will degrade by 3.5dB. See the TypicalPerformance Characteristics section.


WU UU

Figure 7. Transformer Driven ENC/ENC

VDD

LTC1744

1744 F07

BIAS

VDD

5V

ENC

ENCANALOG INPUT

2V BIAS

2V BIAS

1:40.1µF

CLOCKINPUT

50Ω

6k

6k

TO INTERNALADC CIRCUITS

Driving the Encode Inputs

The noise performance of the LTC1744 can depend on theencode signal quality as much as on the analog input. TheENC/ENC inputs are intended to be driven differentially,primarily for noise immunity from common mode noisesources. Each input is biased through a 6k resistor to a 2Vbias. The bias resistors set the DC operating point fortransformer coupled drive circuits and can set the logicthreshold for single-ended drive circuits.

17

LTC1744

1744f


WU UU

Any noise present on the encode signal will result inadditional aperture jitter that will be RMS summed with theinherent ADC aperture jitter.

In applications where jitter is critical (high input frequen-cies) take the following into consideration:

1. Differential drive should be used.

2. Use as large an amplitude as possible; if transformercoupled use a higher turns ratio to increase theamplitude.

3. If the ADC is clocked with a sinusoidal signal, filter theencode signal to reduce wideband noise.

4. Balance the capacitance and series resistance at bothencode inputs so that any coupled noise will appear atboth inputs as common mode noise.

The encode inputs have a common mode range of 1.8V toVDD. Each input may be driven from ground to VDD forsingle-ended drive.

1744 F08a

ENC2V

VTHRESHOLD = 2VENC

0.1µF

LTC1744

1744 F08b

ENC

ENC

130Ω

3.3V

3.3V130Ω

D0

Q0

Q0

MC100LVELT22

LTC1744

83Ω83Ω

Figure 8a. Single-Ended ENC Drive,Not Recommended for Low Jitter Figure 8b. ENC Drive Using a CMOS-to-PECL Translator

Maximum and Minimum Encode Rates

The maximum encode rate for the LTC1744 is 50Msps. Forthe ADC to operate properly the ENCODE signal shouldhave a 50% (±5%) duty cycle. Each half cycle must haveat least 9.5ns for the ADC internal circuitry to have enoughsettling time for proper operation. Achieving a precise50% duty cycle is easy with differential sinusoidal driveusing a transformer or using symmetric differential logicsuch as PECL or LVDS. When using a single-endedENCODE signal asymmetric rise and fall times can resultin duty cycles that are far from 50%.

At sample rates slower than 50Msps the duty cycle canvary from 50% as long as each half cycle is at least 9.5ns.

The lower limit of the LTC1744 sample rate is determinedby droop of the sample-and-hold circuits. The pipelinedarchitecture of this ADC relies on storing analog signals onsmall valued capacitors. Junction leakage will dischargethe capacitors. The specified minimum operating fre-quency for the LTC1744 is 1Msps.

18

LTC1744

1744f

DIGITAL OUTPUTS

Digital Output Buffers

Figure 9 shows an equivalent circuit for a single outputbuffer. Each buffer is powered by OVDD and OGND, iso-lated from the ADC power and ground. The additionalN-channel transistor in the output driver allows operationdown to low voltages. The internal resistor in series withthe output makes the output appear as 50Ω to externalcircuitry and may eliminate the need for external dampingresistors.

Output Loading

As with all high speed/high resolution converters thedigital output loading can affect the performance. Thedigital outputs of the LTC1744 should drive a minimalcapacitive load to avoid possible interaction between thedigital outputs and sensitive input circuitry. The outputshould be buffered with a device such as an ALVCH16373CMOS latch. For full speed operation the capacitive loadshould be kept under 10pF. A resistor in series with theoutput may be used but is not required since the ADC hasa series resistor of 43Ω on chip.

Lower OVDD voltages will also help reduce interferencefrom the digital outputs.

Format

The LTC1744 parallel digital output can be selected foroffset binary or 2’s complement format. The format isselected with the MSBINV pin; high selects offset binary.

Overflow Bit

An overflow output bit indicates when the converter isoverranged or underranged. When OF outputs a logic highthe converter is either overranged or underranged.

Output Clock

The ADC has a delayed version of the ENC input availableas a digital output, CLKOUT. The CLKOUT pin can be usedto synchronize the converter data to the digital system.This is necessary when using a sinusoidal ENCODE. Datawill be updated just after CLKOUT falls and can be latchedon the rising edge of CLKOUT.


WU UU

LTC1744

1744 F09

OVDD

VDD VDD0.1µF

43Ω TYPICALDATAOUTPUT

OGND

OVDD 0.5V TOVDD

PREDRIVERLOGIC

DATAFROM

LATCH

OE

Figure 9. Equivalent Circuit for a Digital Output Buffer

19

LTC1744

1744f

Output Driver Power

Separate output power and ground pins allow the outputdrivers to be isolated from the analog circuitry. The powersupply for the digital output buffers, OVDD, should be tiedto the same power supply as for the logic being driven. Forexample if the converter is driving a DSP powered by a 3Vsupply then OVDD should be tied to that same 3V supply.OVDD can be powered with any voltage up to 5V. The logicoutputs will swing between OGND and OVDD.

Output Enable

The outputs may be disabled with the output enable pin,OE. OE low disables all data outputs including OF andCLKOUT. The data access and bus relinquish times are tooslow to allow the outputs to be enabled and disabledduring full speed operation. The output Hi-Z state isintended for use during long periods of inactivity.

GROUNDING AND BYPASSING

The LTC1744 requires a printed circuit board with a cleanunbroken ground plane. A multilayer board with an inter-nal ground plane is recommended. The pinout of theLTC1744 has been optimized for a flowthrough layout sothat the interaction between inputs and digital outputs isminimized. Layout for the printed circuit board shouldensure that digital and analog signal lines are separated asmuch as possible. In particular, care should be taken notto run any digital track alongside an analog signal track, anencode signal track or underneath the ADC.

High quality ceramic bypass capacitors should be used atthe VDD, VCM, REFHA, REFHB, REFLA and REFLB pins asshown in the block diagram on the front page of this datasheet. Bypass capacitors must be located as close to thepins as possible. Of particular importance are the capaci-tors between REFHA and REFLB and between REFHB andREFLA. These capacitors should be as close to the deviceas possible (1.5mm or less). Size 0402 ceramic capacitors

are recomended. The large 4.7µF capacitor between REFHAand REFLA can be somewhat further away. The tracesconnecting the pins and bypass capacitors must be keptshort and should be made as wide as possible.

The LTC1744 differential inputs should run parallel andclose to each other. The input traces should be as short aspossible to minimize capacitance and to minimize noisepickup.

An analog ground plane separate from the digital process-ing system ground should be used. All ADC ground pinslabeled GND should connect to this plane. All ADC VDDbypass capacitors, reference bypass capacitors and inputfilter capacitors should connect to this analog plane. TheLTC1744 has three output driver ground pins, labeledOGND (Pins 27, 38 and 47). These grounds should con-nect to the digital processing system ground. The outputdriver supply, OVDD should be connected to the digitalprocessing system supply. OVDD bypass capacitors shouldbypass to the digital system ground. The digital process-ing system ground should connected to the analog planeat ADC OGND (Pin 38).

HEAT TRANSFER

Most of the heat generated by the LTC1744 is transferredfrom the die through the package leads onto the printedcircuit board. In particular, ground pins 12, 13, 36 and 37are fused to the die attach pad. These pins have the lowestthermal resistance between the die and the outside envi-ronment. It is critical that all ground pins are connected toa ground plane of sufficient area. The layout of the evalu-ation circuit shown on the following pages has a low ther-mal resistance path to the internal ground plane by usingmultiple vias near the ground pins. A ground plane of thissize results in a thermal resistance from the die to ambientof 35°C/W. Smaller area ground planes or poorly connectedground pins will result in higher thermal resistance.


WU UU

20

LTC1744

1744f

DC3

45B

Eval

uatio

n Ci

rcui

t Sch

emat

ic o

f the

LTC

1744


WU UU

R N1A

33Ω

R633

.2Ω

C4 4.7µ

FC3

10µF

R5 1Ω3 4

1 2

5VU3

LT15

21-3

R N5A

33Ω

R N5B

33Ω

R N5C

33Ω

R N5D

33Ω

R N6A

33Ω

R N6B

33Ω

R N6C

33Ω

R N6D

33Ω

R N7A

33Ω

R N7B

33Ω

R N7C

33Ω

R N7D

33Ω

R N8A

33Ω

R N8B

33Ω

R N1B

33Ω

R N1C

33Ω

R N2A

33Ω

R N2B

33Ω

R N2C

33Ω

R N2D

33Ω

R N3A

33Ω

R N3B

33Ω

R N3C

33Ω

R N3D

33Ω

R N4A

33Ω

R N4B

33Ω

R N4C

33Ω

R N4D

33Ω

C12

0.1µ

F

C10

0.1µ

F

OF

OGND D1

3

D12

D11

OVDD D1

0 D9 D8 D7

OGND GN

D

GND D6 D5 D4

OVDD D3 D2 D1 D0

OGND

CLKO

UT OE

SENS

E

V CM

GND

A IN+

A IN–

GND

V DD

V DD

GND

REFL

B

REFH

A

GND

GND

REFL

A

REFH

B

GND

V DD

V DD

GND

V DD

GND

MSB

INV

ENC

ENC

48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

2OE

2Q8

2Q7

GND

2Q6

2Q5

V CC

2Q4

2Q3

GND

2Q2

2Q1

1Q8

1Q7

GND

1Q6

1Q5

V CC

1Q4

1Q3

GND

1Q2

1Q1

1OE

2LE

2D8

2D7

GND

2D6

2D5

V CC

2D4

2D3

GND

2D2

2D1

1D8

1D7

GND

1D6

1D5

V CC

1D4

1D3

GND

1D2

1D1

1LE

24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

U4P1

74VC

X163

73V

U5LT

C174

4

C19

0.1µ

FC2

00.

1µF

C21

0.1µ

FC2

20.

1µF

1744

TA0

1

C28

0.1µ

F

J232

01S-

40G1

3VU2

10T7

4ALV

C1G8

6JP

2

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

IN TAB

OUT

GND

U1LT

1460

-2.5

V DD

V OUT

C17

4.7µ

FC1

610

µF

E1 5V E2PG

ND

3V

C23

0.1µ

FJP

4JP

3

5V

INPU

TRA

NGE

SELE

CT

TWO

COM

PLEM

ENT

SELE

CT

R Y*

C24*

*18

pF

C25*

*18

pF

C2 4.7µ

FC1

4.7µ

F

5V 5V

*RX,

RY

= IN

PUT

RANG

E SE

T**

DO N

OT IN

STAL

L C2

4, C

25, R

1, R

9 AN

D R1

0

J1ANA

LOG

INPU

T

ENCO

DEIN

PUT

J3 J4

C5 18pF

C29

TBD

R

1**

0Ω

R

10**

0Ω R

9**

10Ω

R8 0Ω

R2 37Ω

T1M

INIC

IRCU

ITS

T1-1

T

R4 100Ω

R3 100Ω

••

R11

50Ω

R22

100Ω

T2M

INIC

IRCU

ITS

T1-1

T

••

R24

2k

R23

3k

R21

100Ω

R7 37Ω

J5

C6 2.2µ

F

C13

0.15

µF

C18

4.7µ

F

C26

0.15

µF

C70.

15µF

C84.

7µF

C9 0.15

µF

C27

0.15

µFC1

50.

15µF

R X*

C14

0.15

µF

C11

1µF

E3 GND

E4 GND

E5 GND

GND

21

LTC1744

1744f

Topside Silkscreen

Topside Copper Layer


WU UUGround Plane, Layer 2

22

LTC1744

1744f

Split Power Plane, Layer 3

Bottom Side Copper, Layer 4


WU UU

23

LTC1744

1744f

FW Package48-Lead Plastic TSSOP (6.1mm)(Reference LTC DWG # 05-08-1651)

PACKAGE DESCRIPTIO

U

FW48 TSSOP 05020.09 – 0.20(.0035 – .008)

0° – 8°

0.45 – 0.75(.018 – .029)

0.17 – 0.27(.0067 – .0106)

0.50(.0197)

BSC

6.0 – 6.2**(.236 – .244)

7.9 – 8.3(.311 – .327)

1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

12.4 – 12.6*(.488 – .496)

1.20(.0473)

MAX

0.05 – 0.15(.002 – .006)

2

48 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 2547

C.10-T--C-

MILLIMETERS(INCHES)

DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDEDIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE

NOTE:1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE*

**

0.32 ±0.05 0.50 TYP

6.2 ±0.108.1 ±0.10

RECOMMENDED SOLDER PAD LAYOUT

0.95 ±0.10

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

24

LTC1744

1744f

LINEAR TECHNOLOGY CORPORATION 2002

LT/TP 0803 1K • PRINTED IN THE USA

PART NUMBER DESCRIPTION COMMENTS

LT®1019 Precision Bandgap Reference 0.05% Max Initial Accuracy, 5ppm/°C Max DriftLTC1196 8-Bit, 1Msps ADC 3V to 5V, SO-8

LTC1405 12-Bit, 5Msps, Sampling ADC with Parallel Output Pin Compatible with the LTC1420

LTC1406 8-Bit, 20Msps ADC Undersampling Capability Up to 70MHz Input

LTC1411 14-Bit, 2.5Msps ADC No Pipeline Delay, 5V, 80dB SINAD

LTC1410 12-Bit, 1.25Msps ADC ±5V, 71dB SINADLTC1412 12-Bit, 3Msps, Sampling ADC with Parallel Output ±5V, No Pipeline Delay, SINAD = 72dB at NyquistLTC1414 14-Bit, 2.2Msps ADC ±5V, No Pipeline Delay, 80dB SINAD, 95dB SFDRLTC1415 Single 5V, 12-Bit, 1.25Msps with Parallel Output 55mW Power Dissipation, 72dB SINAD

LTC1419 14-Bit, 800ksps ADC ±5V, 95dB SFDR, 150mWLTC1420 12-Bit, 10Msps ADC 71dB SINAD and 83dB SFDR at Nyquist

LT1460 Micropower Precision Series Reference 0.075% Accuracy, 10ppm/°C DriftLTC1604/LTC1608 16-Bit, 333ksps/500ksps ADCs 16-Bit, No Missing Codes, 90dB SINAD, –100dB THD

LTC1668 16-Bit, 50Msps DAC 87dB SFDR at 1MHz fOUT, Low Power, Low Cost

LTC1741 12-Bit, 65Msps Low Noise ADC Pin Compatible with the LTC1744







RELATED PARTS

Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

FEATURES DESCRIPTIO U - Analog Devices · 2020. 2. 1. · 1 LTC1744 1744f 14-Bit, 50Msps ADC Sample...

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