LTC2366IS6-TRMPBF

LTC2365/LTC2366 1Msps/3Msps, 12-Bit Serial Sampling ADCs in TSOT FEATURES n n n n n n n n n n n n DESCRIPTION The LTC®2365/LTC2366 are 1Msps/3Msps, 12-bit, sampling A/D converters that draw only 2mA and 2.6mA, respectively, from a single 3V supply. These high performance devices include a high dynamic range sample-and-hold and a high speed serial interface. The full scale input is 0V to VDD or VREF . Outstanding AC performance includes 72dB SINAD and –80dB THD at sample rates of 3Msps. The serial interface provides flexible power management and allows maximum power efficiency at low throughput rates. These devices are available in tiny 6- and 8-lead TSOT-23 packages. The serial interface, tiny TSOT-23 package and extremely high sample rate-to-power ratio make the LTC2365/LTC2366 ideal for compact, low power, high speed systems. The high impedance single-ended analog input and the ability to operate with reduced spans (down to 1.4V full scale) allow direct connection to sensors and transducers in many applications, eliminating the need for gain stages. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. 12-Bit Resolution 1Msps/3Msps Sampling Rates Low Noise: 73dB SNR Low Power Dissipation: 6mW Single Supply 2.35V to 3.6V Operation No Data Latency Sleep Mode with 0.1μA Typical Supply Current Dedicated External Reference (TSOT23-8) 1V to 3.6V Digital Output Supply (TSOT23-8) SPI/MICROWIRE™ Compatible Serial I/O Guaranteed Operation from –40°C to 125°C 6- and 8-Lead TSOT-23 Packages APPLICATIONS n n n n n n n Communication Systems Data Acquisition Systems Handheld Terminal Interface Medical Imaging Uninterrupted Power Supplies Battery Operated Systems Automotive TYPICAL APPLICATION 12-Bit TSOT23-6/-8 ADC Family DATA OUTPUT RATE Part Number 3Msps LTC2366 1Msps LTC2365 500ksps LTC2362 250ksps LTC2361 100ksps LTC2360 0 1MHz Sine Wave 8192 FFT Plot VDD = 3V fSMPL = 3Msps –20 f = 994kHz IN SINAD = 72dB –40 THD = –80.3dB MAGNITUE (dB) –60 –80 –100 –120 –140 0 250 Single 3V Supply, 3Msps, 12-Bit Sampling ADC 3V 10μF LTC2366 VDD VREF GND ANALOG INPUT 0V TO 3V AIN CS SDO SCK OVDD 4.7μF 23656 TA01 SERIAL DATA LINK TO ASIC, PLD, MPU, DSP OR SHIFT REGISTERS DIGITAL OUTPUT SUPPLY 1V TO 3.6V 750 1000 1250 500 INPUT FREQUENCY (kHz) 1500 23656 TA01b 23656f 1 LTC2365/LTC2366 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) Supply Voltage (VDD, OVDD).....................................4.0V VREF and Analog Input Voltage (Note 3).........................................–0.3V to (VDD + 0.3V) Digital Input Voltage......................–0.3V to (VDD + 0.3V) Digital Output Voltage ...................–0.3V to (VDD + 0.3V) Power Dissipation ...............................................100mW Operating Temperature Range LTC2365C/LTC2366C ............................... 0°C to 70°C LTC2365I/LTC2366I.............................. –40°C to 85°C LTC2365H/LTC2366H (Note 13) ......... –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C PIN CONFIGURATION TOP VIEW VDD 1 VREF 2 GND 3 AIN 4 8 CS 7 SCK 6 SDO 5 OVDD VDD 1 GND 2 AIN 3 TOP VIEW 6 CS 5 SDO 4 SCK TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 150°C, θJA = 250°C/W S6 PACKAGE 6-LEAD PLASTIC TSOT-23 TJMAX = 150°C, θJA = 250°C/W ORDER INFORMATION Lead Free Finish TAPE AND REEL (MINI) LTC2366CTS8#TRMPBF LTC2366ITS8#TRMPBF LTC2366HTS8#TRMPBF LTC2366CS6#TRMPBF LTC2366IS6#TRMPBF LTC2366HS6#TRMPBF LTC2365CTS8#TRMPBF LTC2365ITS8#TRMPBF LTC2365HTS8#TRMPBF LTC2365CS6#TRMPBF LTC2365IS6#TRMPBF LTC2365HS6#TRMPBF TAPE AND REEL LTC2366CTS8#TRPBF LTC2366ITS8#TRPBF LTC2366HTS8#TRPBF LTC2366CS6#TRPBF LTC2366IS6#TRPBF LTC2366HS6#TRPBF LTC2365CTS8#TRPBF LTC2365ITS8#TRPBF LTC2365HTS8#TRPBF LTC2365CS6#TRPBF LTC2365IS6#TRPBF LTC2365HS6#TRPBF PART MARKING* LTCYZ LTCYZ LTCYZ LTCXK LTCXK LTCXK LTDCB LTDCB LTDCB LTDCC LTDCC LTDCC PACKAGE DESCRIPTION 8-lead Plastic TSOT-23 8-lead Plastic TSOT-23 8-lead Plastic TSOT-23 6-lead Plastic TSOT-23 6-lead Plastic TSOT-23 6-lead Plastic TSOT-23 8-lead Plastic TSOT-23 8-lead Plastic TSOT-23 8-lead Plastic TSOT-23 6-lead Plastic TSOT-23 6-lead Plastic TSOT-23 6-lead Plastic TSOT-23 TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C –40°C to 125°C 0°C to 70°C –40°C to 85°C –40°C to 125°C 0°C to 70°C –40°C to 85°C –40°C to 125°C 0°C to 70°C –40°C to 85°C –40°C to 125°C TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for information on 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/ 23656f 2 LTC2365/LTC2366 CONVERTER CHARACTERISTICS PARAMETER Resolution (No Missing Codes) Integral Linearity Error Differential Linearity Error Transition Noise Offset Error Gain Error Total Unadjusted Error (Note 5, 6) (Note 6) (Note 7) (Note 6) (Note 6) S6 Package (Note 6) TS8 Package (Note 6) l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) LTC2365 CONDITIONS l l l LTC2366 MAX ±1 ±1 ±3.5 ±2 ±3.5 ±4.5 MIN 12 TYP ±0.25 ±0.25 0.34 2 1 2 3 ±3.5 ±2 ±3.5 ±4.5 MAX ±1 ±1 UNITS Bits LSB LSB LSBRMS LSB LSB LSB LSB MIN 12 TYP ±0.25 ±0.25 0.34 2 1 2 3 ANALOG INPUTS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) PARAMETER Analog Input Voltage Analog Input Leakage Current Analog Input Capacitance Reference Input Voltage Reference Input Leakage Current Reference Input Capacitance Sample-and-Hold Aperture Delay Time Sample-and-Hold Aperture Delay Time Jitter SYMBOL VIN IIN CIN VREF IREF CREF tAP tJITTER CONDITIONS S6 Package TS8 Package CS = High Between Conversions During Conversions TS8 Package TS8 Package TS8 Package l l l l l MIN –0.05 –0.05 TYP MAX VDD + 0.05 VREF + 0.05 ±1 UNITS V V μA pF pF 20 4 1.4 4 1 0.3 VDD + 0.05 ±1 V μA pF ns ns DYNAMIC ACCURACY The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) PARAMETER Signal-to-Noise Ratio Total Harmonic Distortion Spurious Free Dynamic Range Intermodulation Distortion Full Power Bandwidth Full Linear Bandwidth LTC2365 SYMBOL SINAD SNR THD SFDR IMD CONDITIONS l l l LTC2366 TYP MAX UNITS 71 72 –80 82 –71.5 dB MHz MHz MHz –72 dB dB dB 68 69 –72 MIN 68 70 TYP MAX MIN 72 73 –86 87 –76 30 5 2 Signal-to-(Noise + Distortion) Ratio fIN = 1MHz fIN = 1MHz fIN = 1MHz fIN = 1MHz fIN1 = 0.97MHz, fIN2 = 1MHz for LTC2366 fIN1 = 97kHz, fIN2 = 100kHz for LTC2365 At 3dB At 0.1dB SINAD ≥ 68dB 50 8 2.5 23656f 3 LTC2365/LTC2366 DIGITAL INPUTS AND DIGITAL OUTPUTS SYMBOL VIH VIL IIH IIL CIN VOH VOL IOZ COZ ISOURCE ISINK PARAMETER High Level Input Voltage Low Level Input Voltage High Level Input Current Low Level Input Current Digital Input Capacitance High Level Output Voltage Low Level Output Voltage Hi-Z Output Leakage Hi-Z Output Capacitance Output Source Current Output Sink Current VDD = 2.35V to 3.6V, ISOURCE = 200μA VDD = 2.35V to 3.6V, ISINK = 200μA CS = VDD CS = VDD VOUT = 0V VOUT = VDD l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) CONDITIONS 2.7V < VDD ≤ 3.6V 2.35V ≤ VDD ≤ 2.7V 2.7V < VDD ≤ 3.6V 2.35V ≤ VDD ≤ 2.7V VIN = VDD VIN = 0V l l l l l l MIN 2 1.7 TYP MAX UNITS V V 0.8 0.7 2.5 –2.5 2 VDD –0.2 0.2 ±3 4 –10 10 V V μA μA pF V V μA pF mA mA POWER REQUIREMENT SYMBOL VDD OVDD IDD PARAMETER Supply Voltage Digital Output Supply Voltage Supply Current, Static Mode Operational Mode, LTC2366 Operational Mode, LTC2365 Sleep Mode Sleep Mode Power Dissipation, Static Mode Operational Mode, LTC2366 Operational Mode, LTC2365 Sleep Mode Sleep Mode CS = 0V, SCK = 0V or VDD fSMPL = 3Msps fSMPL = 1Msps –40°C to +85°C +85°C to +125°C CS = 0V, SCK = 0V or VDD fSMPL = 3Msps fSMPL = 1Msps –40°C to +85°C +85°C to +125°C CONDITIONS l l l l l l l l l l MIN 2.35 1 TYP 3.0 1 2.6 2 0.1 MAX 3.6 3.6 4 3.5 2 5 3.6 14.4 12.6 7.2 18 UNITS V V mA mA mA μA μA mW mW mW μW μW PD 7.8 6 0.3 23656f 4 LTC2365/LTC2366 The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) LTC2365 SYMBOL fSMPL(MAX) fSCK tSCK tTHROUGHPUT tACQ tCONV tQUIET t1 t2 t3 t4 t5 t6 t7 t8 t9 tPOWER-UP PARAMETER Maximum Sampling Frequency Shift Clock Frequency Shift Clock Period Minimum Throughput Time, tACQ + tCONV Acquisition Time Conversion Time SDO Hi-Z State to CS ↓ SCK↓ Setup Time After CS ↓ SDO Enabled Time After CS ↓ SDO Data Valid Access Time After SCK↓ SCK Low Time SCK High Time SDO Data Valid Hold Time After SCK↓ SDO Into Hi-Z State Time After SCK↓ SDO Into Hi-Z State Time After CS ↑ Power-up Time from Sleep Mode (Notes 8, 9, 11) (Notes 9, 12) (Notes 9, 12) See Sleep Mode section (Notes 8, 9) (Notes 8) (Notes 9, 11, 12) (Notes 8, 9, 11) Minimum Positive or Negative CS Pulse Width (Notes 8) CONDITIONS (Notes 8, 9) (Notes 8, 9, 10) l l l l l l l l l l l l l l l l l TIMING CHARACTERISTICS LTC2366 MAX 16 2000 1000 MIN 3 0.5 20.8 56 277 4 4 2000 4 15 6 2000 4 15 40% 40% 5 30 4.2 1000 5 14 4.2 333 48 2000 333 TYP MAX UNITS MHz MHz ns ns ns ns ns ns ns ns ns tSCK tSCK ns ns ns ns MIN 1 0.5 62.5 181.5 818.5 4 4 6 TYP 40% 40% 5 5 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: All voltage values are with respect to GND. Note 3: When this pin, AIN, is taken below GND or above VDD, it will be clamped by internal diodes. These products can handle input currents greater than 100mA below GND or above VDD without latchup. Note 4: VDD = OVDD = VREF = 2.35V to 3.6V, fSMPL = fSMPL(MAX) and fSCK = fSCK(MAX) unless otherwise specified. Note 5: Integral linearity is defined as the deviation of a code from a straight line passing through the actual endpoints of the transfer curve. The deviation is measured from the center of the quantization band. Note 6: Linearity, offset and gain specifications apply for a single-ended AIN input with respect to GND. Note 7: Typical RMS noise at code transitions. Note 8: Guaranteed by characterization. All input signals are specified with tr = tf = 2ns (10% to 90% of VDD) and timed from a voltage level of 1.6V. Note 9: All timing specifications given are with a 10pF capacitance load. With a capacitance load greater than this value, a digital buffer or latch must be used. Note 10: Minimum fSCK at which specifications are guaranteed. Note 11: The time required for the output to cross the VIH or VIL voltage. Note 12: Guaranteed by design, not subject to test. Note 13: High temperatures degrade operating lifetimes. Operating lifetime is derated at temperatures greater than 105°C. 23656f 5 LTC2365/LTC2366 TYPICAL PERFORMANCE CHARACTERISTICS Integral Nonlinearity vs Output Code 1.0 0.8 0.6 0.4 DNL (LSB) INL (LSB) 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 1024 2048 3072 OUTPUT CODE 4096 23656 G01 TA = 25°C, VDD = OVDD = VREF (LTC2365, Note 4) Integral and Differential Nonlinearity vs Supply Voltage 1.0 0.8 0.6 INL AND DNL (LSB) 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 MIN DNL MIN INL MAX DNL MAX INL Differential Nonlinearity vs Output Code 1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 1024 2048 3072 OUTPUT CODE 4096 23656 G02 VDD = 3V VDD = 3V –1.0 2.1 2.4 3.0 3.3 2.7 SUPPLY VOLTAGE (V) 3.6 23656 G03 Histogram for 16384 Conversions 10000 VDD = 3V 73.5 SNR vs Input Frequency 73.2 VDD = 3.6V SINAD vs Input Frequency VDD = 3.6V 73.0 72.8 VDD = 3V 8000 73.3 SNR (dB) COUNT 6000 73.1 VDD = 3V SINAD (dB) 72.6 72.4 VDD = 2.35V 4000 72.9 VDD = 2.35V 2000 72.7 72.2 72.0 100 INPUT FREQUENCY (kHz) 23656 G05 23656 G06 0 2045 2046 2047 2048 CODE 2049 2050 23656 G04 72.5 100 INPUT FREQUENCY (kHz) 1000 1000 THD vs Input Frequency –81 –82 –83 THD (dB) –84 –85 –86 –87 –88 100 INPUT FREQUENCY (kHz) 23656 G07 THD vs Input Resistance –78 VDD = 3V fSMPL = 1Msps fIN = 1MHz MAGNITUDE (dB) 0 461kHz Sine Wave 8192 FFT Plot VDD = 3V fSMPL = 1Msps –20 f = 461kHz IN SINAD = 72.8dB –40 THD = –86.1dB –60 –80 –100 RIN = 10Ω fSMPL = 1Msps –79 VDD = 3V VDD = 2.35V VDD = 3.6V THD (dB) –80 –81 –82 –120 –83 –140 0 50 25 75 INPUT RESISTANCE (Ω) 100 23656 G08 1000 0 100 200 300 400 INPUT FREQUENCY (kHz) 500 23656 G09 23656f 6 LTC2365/LTC2366 TYPICAL PERFORMANCE CHARACTERISTICS Integral Nonlinearity vs Output Code 1.0 0.8 0.6 0.4 DNL (LSB) INL (LSB) 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 1024 2048 3072 OUTPUT CODE 4096 23656 G10 TA = 25°C, VDD = OVDD = VREF (LTC2366, Note 4) Integral and Differential Nonlinearity vs Supply Voltage 1.0 0.8 0.6 INL AND DNL (LSB) 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 MIN DNL MIN INL MAX DNL MAX INL Differential Nonlinearity vs Output Code 1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 1024 2048 3072 OUTPUT CODE 4096 23656 G11 VDD = 3V VDD = 3V –1.0 2.1 2.4 3.0 3.3 2.7 SUPPLY VOLTAGE (V) 3.6 23656 G12 Histogram for 16384 Conversions 10000 VDD = 3V 73.2 SNR vs Input Frequency 73.0 VDD = 3.6V SINAD vs Input Frequency VDD = 3.6V 72.5 72.0 VDD = 2.35V VDD = 3V 8000 73.0 SINAD (dB) SNR (dB) COUNT 6000 72.8 VDD = 3V 71.5 71.0 4000 72.6 VDD = 2.35V 2000 72.4 70.5 70.0 100 INPUT FREQUENCY (kHz) 23656 G14 23656 G15 0 2045 2046 2047 2048 CODE 2049 2050 23656 G13 72.2 100 INPUT FREQUENCY (kHz) 1000 1500 1000 1500 THD vs Input Frequency –72 –74 -76 THD (dB) THD (dB) –78 –80 VDD = 3.6V –82 –84 VDD = 3V –86 VDD = 2.35V –88 100 INPUT FREQUENCY (kHz) 23656 G16 THD vs Input Resistance –64 –66 –68 –70 –72 –74 –76 –78 0 25 75 INPUT RESISTANCE (Ω) 50 100 23656 G17 1MHz Sine Wave 8192 FFT Plot VDD = 3V fSMPL = 3Msps –20 f = 994kHz IN SINAD = 72dB –40 THD = –80.3dB MAGNITUE (dB) –60 –80 –100 –120 –140 0 250 0 RIN = 10Ω fSMPL = 3Msps VDD = 3V fSMPL = 3Msps fIN = 1.5MHz 1000 1500 750 1000 1250 500 INPUT FREQUENCY (kHz) 1500 23656 G18 23656f 7 LTC2365/LTC2366 TYPICAL PERFORMANCE CHARACTERISTICS Reference Current vs SCK Frequency (TS8 Package) 250 16 SCKS PER CONVERSION NONLINEARITY ERROR (LSB) 1.0 0.8 2.5 2.0 IDD (mA) 1.5 VDD = 2.35V 1.0 0.5 0 0 10 20 30 40 SCK FREQUENCY (MHz) 50 23656 G19 TA = 25°C, VDD = OVDD = VREF (LTC2365/LTC2366, Note 4) Integral and Differential Nonlinearity vs Reference Voltage (TS8 Package) LTC2365, VDD = 3.6V Supply Current vs SCK Frequency 3.0 REFERENCE CURRENT (μA) VDD = 3.6V 200 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0.6 MAX DNL 150 VDD = 3V 100 VDD = 3.6V MAX INL VDD = 3V MIN DNL MIN INL 50 VDD = 2.35V 0 0 5 10 15 20 25 30 35 40 45 50 SCK FREQUENCY (MHz) 23656 G20 1.2 2.4 3.0 1.8 REFERENCE VOLTAGE (V) 3.6 23656 G21 Integral and Differential Nonlinearity vs Reference Voltage (TS8 Package) 1.0 0.8 NONLINEARITY ERROR (LSB) 0.6 MAGNITUDE (dB) 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0.6 –10 1.2 2.4 3.0 1.8 REFERENCE VOLTAGE (V) 3.6 23656 G22 Input Power Bandwidth 2 0 LTC2366 –2 –4 LTC2365 –6 –8 VDD = 3V LTC2366, VDD = 3.6V MAX DNL MAX INL MIN DNL MIN INL 1 10 INPUT FREQUENCY (MHz) 100 23656 G23 23656f 8 LTC2365/LTC2366 PIN FUNCTIONS LTC2365/LTC2366 (S6 Package) VDD (Pin 1): Positive Supply. The VDD range is 2.35V to 3.6V. VDD also defines the input span of the ADC, 0V to VDD. Bypass to GND and to a solid ground plane with a 10μF ceramic capacitor (or 10μF tantalum in parallel with 0.1μF ceramic). GND (Pin 2): Ground. The GND pin must be tied directly to a solid ground plane. AIN (Pin 3): Analog Input. AIN is a single-ended input with respect to GND with a range from 0V to VDD. SCK (Pin 4): Shift Clock Input. The SCK serial clock advances the conversion process. SDO data transitions on the falling edge of SCK. SDO (Pin 5): Three-state Serial Data Output. The A/D conversion result is shifted out on SDO as a serial data stream with MSB first. The data stream consists of two leading zeros followed by 12 bits of conversion data and two trailing zeros. CS (Pin 6): Chip Select Input. This active low signal starts a conversion on the falling edge and frames the serial data transfer. LTC2365/LTC2366 (TS8 Package) VDD (Pin 1): Positive Supply. The VDD range is 2.35V to 3.6V. Bypass to GND and to a solid ground plane with a 10μF ceramic capacitor (or 10μF tantalum in parallel with 0.1μF ceramic). VREF (Pin 2): Reference Input. VREF defines the input span of the ADC, 0V to VREF and the VREF range is 1.4V to VDD. Bypass to GND and to a solid ground plane with a 4.7μF ceramic capacitor (or 4.7μF tantalum in parallel with 0.1μF ceramic). GND (Pin 3): Ground. The GND pin must be tied directly to a solid ground plane. AIN (Pin 4): Analog Input. AIN is a single-ended input with respect to GND with a range from 0V to VREF. OVDD (Pin 5): Output Driver Supply for SDO. The OVDD range is 1V to 3.6V. Bypass to GND and to a solid ground plane with a 4.7μF ceramic capacitor (or 4.7μF tantalum in parallel with 0.1μF ceramic). SDO (Pin 6): Three-state Serial Data Output. The A/D conversion result is shifted out on SDO as a serial data stream with MSB first. The data stream consists of two leading zeros followed by 12 bits of conversion data and two trailing zeros. SCK (Pin 7): Shift Clock Input. The SCK serial clock advances the conversion process. SDO data transitions on the falling edge of SCK. CS (Pin 8): Chip Select Input. This active low signal starts a conversion on the falling edge and frames the serial data transfer. 23656f 9 LTC2365/LTC2366 BLOCK DIAGRAM 10μF 4.7μF VDD 1 ANALOG INPUT RANGE OV TO VREF AIN 4 5 + + OVDD + S&H 12-BIT ADC – VREF THREESTATE SERIAL OUTPUT PORT 6 SDO + 4.7μF GND 2 TIMING LOGIC 3 TS8 PACKAGE 7 SCK 8 CS 23656 BD TIMING DIAGRAMS t8 SCK 1.6V SDO Hi-Z 23656 TD01 Figure 1. SDO Into Hi-Z State After SCK Falling Edge t7 SCK 1.6V SDO VIH VIL 23656 TD02 Figure 2. SDO Data Valid Hold Time After SCK Falling Edge t4 SCK 1.6V SDO VOH VOL 23656 TD03 Figure 3. SDO Data Valid Access Time After SCK Falling Edge 23656f 10 LTC2365/LTC2366 APPLICATIONS INFORMATION DC PERFORMANCE The noise of an ADC can be evaluated in two ways: signalto-noise ratio (SNR) in the frequency domain and histogram in the time domain. The LTC2365/LTC2366 excel in both. Figures 5 and 6 demonstrate that the LTC2365/LTC2366 have an SNR of over 72dB. The noise in the time domain histogram is the transition noise associated with a 12-bit resolution ADC which can be measured with a fixed DC signal applied to the input of the ADC. The resulting output codes are collected over a large number of conversions. The shape of the distribution of codes will give an indication of the magnitude of the transition noise. In Figure 4, the distribution of output codes is shown for a DC input that has been digitized 16384 times. The distribution is Gaussian and the RMS code transition is about 0.34LSB. This corresponds to a noise level of 72.7dB relative to a full scale of 3V. DYNAMIC PERFORMANCE The LTC2365/LTC2366 have excellent high speed sampling capability. Fast fourier transform (FFT) test techniques are used to test the ADC’s frequency response, distortion and noise at the rated throughput. By applying a low distortion sine wave and analyzing the digital output using an FFT algorithm, the ADC’s spectral content can be examined for frequencies outside the fundamental. Figures 5 and 6 show typical LTC2365 and LTC2366 FFT plots respectively. VDD = 3V fSMPL = 1Msps –20 fIN = 461kHz SINAD = 72.8dB –40 THD = –86.1dB –60 –80 –100 –120 –140 0 100 200 300 400 INPUT FREQUENCY (kHz) 500 23656 F05 0 MAGNITUDE (dB) Figure 5. LTC2365 FFT Plot 10000 VDD = 3V VDD = 3V fSMPL = 3Msps –20 f = 994kHz IN SINAD = 72dB –40 THD = –80.3dB MAGNITUE (dB) –60 –80 –100 2000 –120 –140 2045 2046 2047 2048 CODE 2049 2050 23656 F04 0 8000 COUNT 6000 4000 0 0 250 750 1000 1250 500 INPUT FREQUENCY (kHz) 1500 23656 F06 Figure 4. Histogram for 16384 Conversions Figure 6. LTC2366 FFT Plot 23656f 11 LTC2365/LTC2366 APPLICATIONS INFORMATION Signal-to-Noise plus Distortion Ratio The signal-to-noise plus distortion ratio (SINAD) is the ratio between the RMS amplitude of the fundamental input frequency to the RMS amplitude of all other frequency components at the A/D output. The output is band limited to frequencies from above DC and below half the sampling frequency. Figure 6 shows a typical FFT with a 3MHz sampling rate and a 1MHz input. The dynamic performance is excellent for input frequencies up to and beyond the Nyquist frequency of 1.5MHz. Effective Number of Bits The effective number of bits (ENOB) is a measurement of the resolution of an ADC and is directly related to SINAD by the equation: ENOB = (SINAD – 1.76)/6.02 where ENOB is the effective number of bits of resolution and SINAD is expressed in dB. At the maximum 73.0 VDD = 3.6V 72.5 72.0 SINAD (dB) 71.5 71.0 70.5 70.0 100 INPUT FREQUENCY (kHz) 23656 F07 sampling rate of 3MHz, the LTC2366 maintains ENOB above 11 bits up to the Nyquist input frequency of 1.5MHz (refer to Figure 7). Total Harmonic Distortion The total harmonic distortion (THD) is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as: V1 where V1 is the RMS amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the second through nth harmonics. THD versus Input Frequency is shown in Figure 8. The LTC2366 has excellent distortion performance up to the Nyquist frequency and beyond. –72 –74 –76 RIN = 10Ω THD = 20log V2 2 + V3 2 + V4 2 + ...Vn 2 11.83 VDD = 2.35V VDD = 3V 11.67 THD (dB) ENOB 11.50 11.34 1000 1500 –78 –80 VDD = 3.6V –82 –84 –86 VDD = 2.35V –88 100 INPUT FREQUENCY (kHz) 23656 F08 VDD = 3V 1000 1500 Figure 7. LTC2366 ENOB and SINAD vs Input Frequency Figure 8. LTC2366 Distortion vs Input Frequency 23656f 12 LTC2365/LTC2366 APPLICATIONS INFORMATION Intermodulation Distortion If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermoduation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency. If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at the sum and difference frequencies of mfa±nfb, where m and n = 0, 1, 2, 3, etc. For example, the 2nd order IMD terms include (fa ± fb). If the two input sine waves are equal in magnitude, the value (in decibels) of the 2nd order IMD products can be expressed by the following formula: Amplitude at (fa ± fb ) IMD(fa ± fb ) = 20log Amplitude at fa The LTC2365/LTC2366 have good IMD as shown in Figure 9a and Figure 9b respectively. VDD = 3V = 1Msps f –20 fSMPL96kHz b=3 fb = 424kHz –40 IMD = –73.5dB MAGNITUE (dB) –60 –80 –100 –120 –140 0 50 100 150 200 250 300 350 400 450 500 INPUT FREQUENCY (kHz) 23656 F09a Peak Harmonic or Spurious Noise The peak harmonic or spurious noise is the largest spectral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of a full-scale input signal. Full-Power and Full-Linear Bandwidth The full-power bandwidth is that input frequency at which the amplitude of reconstructed fundamental is reduced by 3dB for full-scale input signal. The full-linear bandwidth is the input frequency at which the SINAD has dropped to 68dB (11 effective bits). The LTC2365/LTC2366 have been designed to optimize input bandwidth, allowing the ADC to undersample input signals with frequencies above the converter’s Nyquist Frequency. The noise floor stays very low at high frequencies; SINAD becomes dominated by distortion at frequencies far beyond Nyquist. 0 MAGNITUDE (dB) VDD = 3V fSMPL = 3Msps –20 f = 935kHz a fb = 1.045kHz –40 IMD = –71.5dB –60 –80 –100 –120 –140 0 250 0 750 1000 1250 500 INPUT FREQUENCY (kHz) 1500 23656 F09b Figure 9a. LTC2365 Intermodulation Distortion Plot Figure 9b. LTC2366 Intermodulation Distortion Plot 23656f 13 LTC2365/LTC2366 APPLICATIONS INFORMATION OVERVIEW The LTC2365/LTC2366 use a successive approximation algorithm and internal sample-and-hold circuit to convert an analog signal to a 12-bit serial output. Both devices operate from a single 2.35V to 3.6V supply. The LTC2366 samples at a rate of 3Msps with a 48MHz clock while the LTC2365 samples at a rate of 1Msps with a 16MHz clock. The LTC2365/LTC2366 contain a 12-bit, switched-capacitor ADC, a sample-and-hold, and a serial interface (see Block Diagram) and are available in tiny 6- and 8-lead TSOT-23 packages. The devices provide sleep mode control through the serial interface to save power during inactive periods (see the SLEEP MODE section). The S6 package of the LTC2365/LTC2366 uses VDD as the reference and has an analog input range of 0V to VDD. The ADC samples the analog input with respect to GND and outputs the result through the serial interface. The TS8 package provides two additional pins: a reference input pin, VREF, and an output supply pin, OVDD. The ADC can operate with reduced spans down to 1.4V and achieve 342μV resolution. OVDD controls the output swing of the digital output pin, SDO, and allows the device to communicate with 1.8V, 2.5V or 3V digital systems. SERIAL INTERFACE The LTC2365/LTC2366 communicate with microcontrollers, DSPs and other external circuitry via a 3-wire interface. Figure 10 shows the serial interface timing diagram, while Figures 11 and 12 detail the timing diagrams of conversion cycles in 14 and 16 SCK cycles respectively. Data Transfer A falling CS edge starts a conversion and frames the serial data transfer. SCK provides the conversion clock and controls the data transfer during the conversion. CS going low clocks out the first leading zero and subsequent SCK falling edges clock out the remaining data, beginning with the second leading zero. (Therefore, the first SCK falling edge captures the first leading zero and clocks out the second leading zero). The timing diagram in Figure 12 shows that the final bit in the data transfer is valid on the 16th falling edge, since it is clocked out on the previous 15th falling edge. In applications with a slower SCK, it is possible to capture data on each SCK rising edge. In such cases, the first falling edge of SCK clocks out the second leading zero and can be captured on the first rising edge. However, the first leading zero clocked out when CS goes low is missed as shown in Figures 11 and 12. In Figure 12, the 15th falling edge of SCK clocks out the last bit and can be captured on the 15th rising SCK edge. If CS goes low while SCK is low, then CS clocks out the first leading zero and can be captured on the SCK rising edge. The next SCK falling edge clocks out the second leading zero and can be captured on the following rising edge as shown in in Figure 10. t1 CS tCONV t2 SCK t3 SDO ZERO ZERO B11 (MSB) 13tSCK tTHROUGHPUT 23656 F10 t6 1 2 3 4 t4 B10 B9 5 t7 B1 B0 13 14 t5 ZERO ZERO tACQ 15 16 t8 tQUIET Hi-Z STATE Figure 10. LTC2365/LTC2366 Serial Interface Timing Diagram 23656f 14 LTC2365/LTC2366 APPLICATIONS INFORMATION Achieving 3Msps Sample Rate with LTC2366 CS going low places the sample-and-hold into hold mode and starts a conversion. The LTC2365/LTC2366 require at least 14 SCK cycles to finish the conversion. The conversion terminates after the 13th falling SCK edge, which clocks out B0. The 14th falling SCK edge places the sample-and-hold back into sample mode. Ignoring the last two trailing zeros, the user can bring CS high after the 14th falling SCK edge. The user can also keep the last two trailing zeros by bringing CS high right after the 16th falling SCK. In both cases, a sample rate of 3Msps can be achieved by using a 48MHz SCK clock on the LTC2366, where tTHROUGHPUT is 333ns. Serial Data Output (SDO) The SDO output remains in the high impedance state while CS is high. The falling edge of CS starts the conversion and enables SDO. The A/D conversion result is shifted out on the SDO pin as a serial data stream with the MSB first. The data stream consists of two leading zeros followed by 12 bits of conversion data and two trailing zeros. The SDO output returns to the high impedance state at the 16th falling edge of SCK or sooner by bringing ⎯C⎯S high before the 16th falling edge of SCK. The output swing on the SDO pin is controlled by the VDD pin voltage in the S6 package and by the OVDD pin voltage in the TS8 package. t1 CS tCONV t2 SCK 1 t3 SDO Z ZERO B11 (MSB) tTHROUGHPUT 23656 F11 tACQ t6 4 t4 5 t7 B1 13 t5 B0 14 t9 tQUIET Hi-Z STATE 2 3 B10 B9 Figure 11. LTC2365/LTC2366 Serial Interface Timing Diagram for 14 SCK Cycles t1 CS tCONV t2 SCK 1 t3 SDO Z ZERO B11 (MSB) tTHROUGHPUT 23656 F12 tACQ t6 4 t4 5 t7 B1 B0 13 14 t5 ZERO ZERO Hi-Z STATE 15 16 t8 OR t9 tQUIET 2 3 B10 B9 Figure 12. LTC2365/LTC2366 Serial Interface Timing Diagram for 16 SCK Cycles 23656f 15 LTC2365/LTC2366 APPLICATIONS INFORMATION SLEEP MODE The LTC2365/LTC2366 provide a sleep mode to conserve power during inactive periods. Upon power-up, holding CS high initializes the ADC to sleep mode. In sleep mode, all bias circuitry is shut down and only leakage currents remain (0.1μA typ). Entering Sleep Mode The ADC achieves the fastest sampling rate in operational mode (full power-up). The device can also be put into sleep mode for power savings during inactive periods. To force the LTC2365/LTC2366 into sleep mode, the user can interrupt the conversion process by bringing CS high between the 2nd and 10th falling edges of SCK (see Figures 13 and 14). If CS is brought high after the 10th falling edge and before the 16th falling edge, the device remains powered up, but the conversion is terminated and SDO returns to the high impedance state. CS 1 SCK SDO 2 10 12 14 16 VALID DATA 23656 F13 Figure 13. LTC2365/LTC2366 Operational Mode CS 1 SCK 2 10 12 14 16 SDO Hi-Z STATE 23656 F14 Figure 14. LTC2365/LTC2366 Entering Sleep Mode 23656f 16 LTC2365/LTC2366 APPLICATIONS INFORMATION Exiting Sleep Mode and Power-Up Time To exit sleep mode, pull CS low and perform a dummy conversion. The LTC2365/LTC2366 device power up completely after the 16th falling edge of SCK. After powering up, the ADC can continuously acquire an input signal and perform conversions as described in the SERIAL INTERFACE section (see Figure 15). The wake-up time is 333ns for the LTC2366 with a 48MHz SCK and 1μs for the LTC2365 with a 16MHz SCK. The sample-and-hold is in hold mode while the device is in sleep mode. The ADC returns to sample mode after the 1st falling edge of SCK during power-up (see Figure 15). THE DEVICE BEGINS TO POWER UP THE DEVICE BEGINS TO ACQUIRE INPUT tPOWER-UP THE DEVICE IS FULLY POWERED UP AND READY TO PERFORM CONVERSION POWER VERSUS SAMPLING RATE Figure 16 shows the power consumption of the LTC2365/ LTC2366 in operational mode. By taking the ADC into sleep mode when not performing a conversion, the average power consumption of the ADC decreases as the sampling rate decreases. Figure 17 shows the power consumption versus sampling rate with the device in sleep mode when not performing a conversion. CS 1 SCK SDO 2 10 12 14 16 12 10 12 14 16 INVALID DATA VALID DATA 23656 F15 Figure 15. LTC2365/LTC2366 Exiting Sleep Mode 7.5 7.0 6.5 POWER (mW) POWER (mW) 6.0 5.5 5.0 4.5 4.0 3.5 3.0 0 500 1000 1500 2000 SAMPLE RATE (ksps) 2500 3000 VDD = 3V fSCK = VARIABLE 16 SCKS PER CONVERSION 8 VDD = 3V 7 fSCK = 48MHz 6 5 4 3 2 1 0 0 500 250 750 SAMPLE RATE (ksps) 1000 23656 F17 23656 F16 Figure 16. Power Consumption vs Sample Rate while the Device Remains Powered Up Continuously Figure 17. Power Consumption vs Sample Rate while the Device Enters Sleep Mode when not Performing Conversions 23656f 17 LTC2365/LTC2366 APPLICATIONS INFORMATION SINGLE-ENDED ANALOG INPUT Driving the Analog Input The analog input of the LTC2365/LTC2366 is easy to drive. The input draws only one small current spike while charging the sample-and-hold capacitor at the end of conversion. During the conversion, the analog input draws only a small leakage current. If the source impedance of the driving circuit is low, then the input of the LTC2365/LT2366 can be driven directly. As source impedance increases, so will acquisition time. For minimum acquisition time with high source impedance, a buffer amplifier should be used. The main requirement is that the amplifier driving the analog input must settle after the small current spike before the next conversion starts (settling time must be less than 56ns for full throughput rate). While choosing an input amplifier, also keep in mind the amount of noise and harmonic distortion the amplifier contributes. Choosing an Input Amplifier Choosing an input amplifier is easy if a few requirements are taken into consideration. First, to limit the magnitude of the voltage spike seen by amplifier from charging the sampling capacitor, choose an amplifier that has a low output impedance (