LTC2321-12 Dual, 12-Bit + Sign, 2Msps Differential Input ADC with Wide Input Common Mode Range Description Features n n n n n n n n n n n n n 2Msps Throughput Rate ±0.5LSB INL (Typ) Guaranteed 12-Bit, No Missing Codes 8VP-P Differential Inputs with Wide Input Common Mode Range 73dB SNR (Typ) at fIN = 500kHz –85dB THD (Typ) at fIN = 500kHz Guaranteed Operation to 125°C Single 3.3V or 5V Supply Low Drift (20ppm/°C Max) 2.048V or 4.096V Internal Reference 1.8V to 2.5V I/O Voltages CMOS or LVDS SPI-Compatible Serial I/O Power Dissipation 30mW/Ch (Typ) Small 28-Lead (4mm × 5mm) QFN Package The LTC®2321-12 is a low noise, high speed dual 12-bit + sign successive approximation register (SAR) ADC with differential inputs and wide input common mode range. Operating from a single 3.3V or 5V supply, the LTC2321-12 has an 8VP-P differential input range, making it ideal for applications which require a wide dynamic range with high common mode rejection. The LTC2321-12 achieves ±0.5LSB INL typical, no missing codes at 12 bits and 73dB SNR. The LTC2321-12 has an onboard low drift (20ppm/°C max) 2.048V or 4.096V temperature-compensated reference. The LTC2321-12 also has a high speed SPI-compatible serial interface that supports CMOS or LVDS. The fast 2Msps per channel throughput with zero cycle latency makes the LTC2321-12 ideally suited for a wide variety of high speed applications. The LTC2321-12 dissipates only 30mW per channel and offers nap and sleep modes to reduce the power consumption to 5μW for further power savings during inactive periods. Applications n n n n n n n High Speed Data Acquisition Systems Communications Remote Data Acquisition Imaging Optical Networking Automotive Multiphase Motor Control L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application DIFFERENTIAL INPUTS NO CONFIGURATION REQUIRED VDD REFOUT1 AIN1+ VBYP1 LTC2321-12 0V REFOUT2 220pF VBYP2 BIPOLAR UNIPOLAR 25Ω 0V 0V AIN1– AIN2+ AIN2– VDD CMOS/LVDS REFINT GND SDO1 SDO2 CLKOUT SCK CNV OGND OVDD 10µF AMPLITUDE (dBFS) DIFFERENTIAL 25Ω 0V 0 10µF IN+, IN – INSTRUMENTATION 32k Point FFT fS = 2Msps, fIN = 500klHz 3.3V OR 5V 1µF 10µF 1µF TO CONTROL LOGIC (FPGA, CPLD, DSP, ETC.) 1.8V TO 2.5V SNR = 72.9dB THD = –86.1dB –20 SINAD = 72.8dB SFDR = 89.5dB –40 –60 –80 –100 –120 –140 1µF 232112 TA01a 0 0.2 0.4 0.6 FREQUENCY (MHz) 0.8 1 232112 TA01b 232112fa For more information www.linear.com/LTC2321-12 1 LTC2321-12 Absolute Maximum Ratings Pin Configuration (Notes 1, 2) OGND VBYP2 CMOS/LVDS REFOUT2 REFRTN2 REFINT TOP VIEW 28 27 26 25 24 23 VDD 1 22 SCK – AIN2+ 2 21 SCK+ 20 SDO2 – AIN2 – 3 29 GND GND 4 GND 5 19 SDO2+ 18 CLKOUT – AIN1 – 6 17 CLKOUT+ AIN1+ 7 16 SDO1 – VDD 8 15 SDO1+ OVDD VBYP1 REFOUT1 REFRTN1 CNV 9 10 11 12 13 14 GND Supply Voltage (VDD)...................................................6V Supply Voltage (OVDD).................................................3V Supply Bypass Voltage (VBYP1, VBYP2)........................3V Analog Input Voltage AIN+, AIN – (Note 3).................... –0.3V to (VDD + 0.3V) REFOUT1,2.............................. .–0.3V to (VDD + 0.3V) CNV (Note 15)........................... –0.3V to (VDD + 0.3V) Digital Input Voltage (Note 3)........................... (GND – 0.3V) to (OVDD + 0.3V) Digital Output Voltage (Note 3)........................... (GND – 0.3V) to (OVDD + 0.3V) Power Dissipation................................................200mW Operating Temperature Range LTC2321C................................................. 0°C to 70°C LTC2321I..............................................–40°C to 85°C LTC2321H........................................... –40°C to 125°C Storage Temperature Range................... –65°C to 150°C UFD PACKAGE 28-LEAD (4mm × 5mm) PLASTIC QFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2321CUFD-12#PBF LTC2321CUFD-12#TRPBF 23212 28-Lead (4mm × 5mm) Plastic QFN 0°C to 70°C LTC2321IUFD-12#PBF LTC2321IUFD-12#TRPBF 23212 28-Lead (4mm × 5mm) Plastic QFN –40°C to 85°C LTC2321HUFD-12#PBF LTC2321HUFD-12#TRPBF 23212 28-Lead (4mm × 5mm) Plastic QFN –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For 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/ Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 4). SYMBOL PARAMETER CONDITIONS MAX UNITS VIN+ Absolute Input Range (AIN1+, AIN2+) (Note 5) l MIN 0 TYP VDD V VIN– Absolute Input Range (AIN1–, AIN2–) (Note 5) l 0 VDD V VIN+ – VIN– Input Differential Voltage Range VIN = VIN+ – VIN– l –REFOUT1,2 REFOUT1,2 V VCM Common Mode Input Range VIN = (VIN+ + VIN–)/2 l 0 VDD V IIN Analog Input DC Leakage Current l –1 1 µA CIN Analog Input Capacitance CMRR Input Common Mode Rejection Ratio IREFOUT External Reference Current 2 10 pF fIN = 2.2MHz 85 dB REFINT = 0V, REFOUT = 4.096V 310 µA 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Converter Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Notes 4, 16). SYMBOL PARAMETER CONDITIONS MIN MAX UNITS Resolution 12 Bits No Missing Codes l 12 Bits l –1 ±0.5 1 LSB l –0.99 ±0.4 0.99 LSB l –1.5 0 1.5 Transition Noise INL Integral Linearity Error DNL Differential Linearity Error BZE Bipolar Zero-Scale Error 0.4 (Note 6) (Note 7) Bipolar Zero-Scale Error Drift FSE TYP l LSBRMS 0.0015 Bipolar Full-Scale Error VREFOUT1,2 = 4.096V (REFINT Grounded) (Note 7) Bipolar Full-Scale Error Drift VREFOUT1,2 = 4.096V (REFINT Grounded) l –23 ±2 LSB LSB/°C 23 15 LSB ppm/°C Dynamic Accuracy The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C and AIN = –1dBFS (Notes 4, 8). SYMBOL PARAMETER CONDITIONS SINAD Signal-to-(Noise + Distortion) Ratio fIN = 500kHz, VREFOUT1,2 = 4.096V, Internal Reference fIN = 500kHz, VREFOUT1,2 = 5V, External Reference l SNR Signal-to-Noise Ratio fIN = 500kHz, VREFOUT1,2 = 4.096V, Internal Reference l MIN TYP 69.5 72.8 dB 73 dB 70 fIN = 500kHz, VREFOUT1,2 = 5V, External Reference THD Total Harmonic Distortion fIN = 500kHz, VREFOUT1,2 = 4.096V, Internal Reference SFDR Spurious Free Dynamic Range fIN = 500kHz, VREFOUT1,2 = 4.096V, Internal Reference fIN = 500kHz, VREFOUT1,2 = 5V, External Reference l 78 UNITS 73 dB 73.5 dB –85 l fIN = 500kHz, VREFOUT1,2 = 5V, External Reference MAX –80 dB –84 dB 88 dB 88 dB –3dB Input Linear Bandwidth 10 MHz Aperture Delay 500 ps Aperture Delay Matching 500 ps Aperture Jitter Transient Response Full-Scale Step 1 psRMS 3 ns 232112fa For more information www.linear.com/LTC2321-12 3 LTC2321-12 Internal Reference Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 4). SYMBOL PARAMETER CONDITIONS VREFOUT1,2 Internal Reference Output Voltage 4.75V < VDD < 5.25V 3.13V < VDD < 3.47V l l VREFOUT Temperature Coefficient (Note 14) l MIN TYP MAX UNITS 4.088 2.044 4.096 2.048 4.106 2.053 V 3 20 REFOUT1,2 Output Impedance VREFOUT1,2 Line Regulation ppm/°C 0.25 Ω 0.3 mV/V VDD = 4.75V to 5.25V Digital Inputs And Digital Outputs The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 4). SYMBOL PARAMETER CONDITIONS MIN VIH High Level Input Voltage l VIL Low Level Input Voltage l IIN Digital Input Current CIN Digital Input Capacitance VOH TYP MAX 0.8 • OVDD VIN = 0V to OVDD l –10 High Level Output Voltage IO = -500µA l OVDD – 0.2 VOL Low Level Output Voltage IO = 500µA l l UNITS V 0.2 • OVDD V 10 μA 5 pF V 0.2 IOZ Hi-Z Output Leakage Current VOUT = 0V to OVDD ISOURCE Output Source Current VOUT = 0V ISINK Output Sink Current VOUT = OVDD VID LVDS Differential Input Voltage 100Ω Differential Termination, OVDD = 2.5V l 240 600 mV VIS LVDS Common Mode Input Voltage 100Ω Differential Termination, OVDD = 2.5V l 1 1.45 V VOD LVDS Differential Output Voltage 100Ω Differential Load, LVDS Mode, OVDD = 2.5V l 100 150 300 mV VOS LVDS Common Mode Output Voltage 100Ω Differential Load, LVDS Mode, OVDD = 2.5V l 0.85 1.2 1.4 V VOD_LP Low Power LVDS Differential Output Voltage 100Ω Differential Load, Low Power, LVDS Mode ,OVDD = 2.5V l 75 100 250 mV VOS_LP Low Power LVDS Common Mode Output Voltage 100Ω Differential Load, Low Power, LVDS Mode ,OVDD = 2.5V l 0.9 1.2 1.4 V 4 –10 10 V –10 µA mA 10 mA 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Power Requirements The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 4). SYMBOL PARAMETER VDD Supply Voltage OVDD Supply Voltage CONDITIONS MIN 5V Operation 3.3V Operation IVDD Supply Current 2Msps Sample Rate (IN+ = IN– = 0V) IOVDD Supply Current 2Msps Sample Rate (CL = 5pF) 2Msps Sample Rate (RL = 100Ω) INAP Nap Mode Current Conversion Done (IVDD) ISLEEP Sleep Mode Current Sleep Mode (IVDD + IOVDD) Sleep Mode (IVDD + IOVDD) PD_3.3V Power Dissipation PD_5V MAX UNITS l l 4.75 3.13 TYP 5.25 3.47 V V l 1.71 2.63 V l 11.8 15 mA l l 1.8 7.1 2 11 mA mA l 2.55 5 mA l l 1 1 5 5 μA μA VDD = 3.3V 2Msps Sample Rate (IN+ = IN– = 0V) CMOS Mode VDD = 3.3V 2Msps Sample Rate (IN+ = IN– = 0V) LVDS Mode 37 52 58 86 mW mW Nap Mode VDD = 3.3V Conversion Done (IVDD + IOVDD) VDD = 3.3V Conversion Done (IVDD + IOVDD) CMOS Mode LVDS Mode 7.8 26 13 41 mW mW Sleep Mode VDD = 3.3V Sleep Mode (IVDD + IOVDD) VDD = 3.3V Sleep Mode (IVDD + IOVDD) CMOS Mode LVDS Mode 5 5 16.5 16.5 μW μW Power Dissipation VDD = 5V 2Msps Sample Rate (IN+ = IN– = 0V) CMOS Mode VDD = 5V 2Msps Sample Rate (IN+ = IN– = 0V) LVDS Mode 60 77 80 102.5 mW mW Nap Mode VDD = 5V Conversion Done (IVDD + IOVDD) VDD = 5V Conversion Done (IVDD + IOVDD) CMOS Mode LVDS Mode 13 31 25 40 mW mW Sleep Mode VDD = 5V Sleep Mode (IVDD + IOVDD) VDD = 5V Sleep Mode (IVDD + IOVDD) CMOS Mode LVDS Mode 5 5 25 25 μW μW CMOS Mode LVDS Mode CMOS Mode LVDS Mode 232112fa For more information www.linear.com/LTC2321-12 5 LTC2321-12 ADC Timing Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 4). SYMBOL PARAMETER CONDITIONS fSMPL Maximum Sampling Frequency tCYC Time Between Conversions MIN TYP l (Note 11) tCYC = tCNVH + tCONV + tREADOUT l 500 MAX UNITS 2 Msps 1000000 ns tCONV Conversion Time l 220 ns tCNVH CNV High Time l 30 ns tDSCKHNVH SCK Delay Time to CNV↑ (Note 11) l 0 ns tSCK SCK Period (Notes 12, 13) l 15.6 ns tSCKH SCK High Time l 7 ns tSCKL SCK Low Time l 7 ns tDSCKCLKOUT SCK to CLKOUT Delay (Note 12) l 2.8 tDCLKOUTSDOV SDO Data Valid Delay from CLKOUT↓ CL = 5pF (Note 12) l 2.5 ns tHSDO SDO Data Remains Valid Delay from CLKOUT↓ CL = 5pF (Note 11) l 2.5 ns tDCNVSDOV SDO Data Valid Delay from CNV↓ CL = 5pF (Note 11) l 3 ns tDCNVSDOZ Bus Relinquish Time After CNV↑ (Note 11) l tWAKE REFOUT1,2 Wake-Up Time CREFOUT1,2 = 10μF 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 ground. Note 3: When these pin voltages are taken below ground, or above VDD or OVDD, they will be clamped by internal diodes. This product can handle input currents up to 100mA below ground, or above VDD or OVDD, without latch-up. Note 4: VDD = 5V, OVDD = 2.5V, REFOUT1,2 = 4.096V, fSMPL = 2MHz. Note 5: Recommended operating conditions. Note 6: Integral nonlinearity 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 7: Bipolar zero error is the offset voltage measured from –0.5LSB when the output code flickers between 0 0000 0000 0000 and 1 1111 1111 1111. Full-scale bipolar error is the worst-case of –FS or +FS untrimmed deviation from ideal first and last code transitions and includes the effect of offset error. ns 2.5 3 10 ns ms Note 8: All specifications in dB are referred to a full-scale ±4.096V input with REFOUT = 4.096V. Note 9: When REFOUT1,2 is overdriven, the internal reference buffer must be turned off by setting REFINT = 0V. Note 10: fSMPL = 2MHz, IREFBUF varies proportionally with sample rate. Note 11: Guaranteed by design, not subject to test. Note 12: Parameter tested and guaranteed at OVDD = 1.71V and OVDD = 2.5V. Note 13: tSCK of 15.6ns maximum allows a shift clock frequency up to 64MHz for rising edge capture. Note 14: Temperature coefficient is calculated by dividing the maximum change in output voltage by the specified temperature range. Note 15: CNV is driven from a low jitter digital source, typically at OVDD logic levels. This input pin has a TTL style input that will draw a small amount of current. Note 16: 1LSB = 2 • REFOUT1,2/212 0.8 • OVDD tWIDTH 0.2 • OVDD tDELAY tDELAY 0.8 • OVDD 0.8 • OVDD 0.2 • OVDD 0.2 • OVDD 50% 50% 232112 F01 Figure 1. Voltage Levels for Timing Specifications 6 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Typical Performance Characteristics 4.096V, fSMPL = 2Msps, unless otherwise noted (Note 16). Integral Nonlinearity vs Output Code TA = 25°C, VDD = 5V, OVDD = 2.5V, REFOUT1,2 = Differential Nonlinearity vs Output Code 1.0 DC Histogram 1.00 70000 0.80 0 –0.5 50000 0.40 0.20 COUNTS DNL ERROR (LSB) INL ERROR (LSB) 60000 0.60 0.5 0 –0.20 –0.40 10000 –0.80 0 –2048 2048 OUTPUT CODE 4096 –1.00 –4096 –85 –100 SNR 73.0 SINAD 72.5 72.0 71.5 0.2 0.4 0.6 0.8 FREQUENCY (MHz) 71.0 1 0 0.5 FREQUENCY (MHz) 232112 G04 THD, Harmonics vs Input Common Mode 2 232112 G03 1 THD –95 HD2 –100 HD3 –105 –110 0 0.25 232112 G05 0.50 0.75 FREQUENCY (MHz) 1 232112 G06 8k Point FFT, IMD, fS = 2Msps, VIN+ = 100kHz, VIN– = 500kHz 0 SNR 73 –80 –20 SINAD SNR, SINAD (dBFS) THD –90 –95 HD2 –100 HD3 71 AMPLITUDE (dBFS) –85 69 67 –105 –110 1.7 1 –90 SNR, SINAD vs Reference Voltage, fIN = 500kHz –75 0 CODE –1 THD, Harmonics vs Input Frequency (50kHz to 1MHz) THD, HARMONICS (dBFS) –80 –2 232112 G02 73.5 –60 0 0 4096 74.0 SNR = 72.9dB THD = –86.1dB –20 SINAD = 72.8dB SFDR = 89.5dB –40 SNR, SINAD (dBFS) AMPLITUDE (dBFS) 2048 SNR, SINAD vs Input Frequency (50kHz to 1MHz) –120 THD, HARMONICS (dBFS) 0 OUTPUT CODE 0 –140 –2048 232112 G01 32k Point FFT, fS =2Msps, fIN = 500kHz 30000 20000 –0.60 –1.0 –4096 40000 –40 –60 –80 –100 –120 1.9 2.1 2.3 2.5 2.7 2.9 INPUT COMMON MODE (V) 3.1 3.3 232112 G07 65 0.5 1 1.5 2 2.5 3 VREF (V) 3.5 4 4.5 5 232112 G08 –140 0 0.2 0.4 0.6 FREQUENCY (MHz) 0.8 1.0 232112 G09 232112fa For more information www.linear.com/LTC2321-12 7 LTC2321-12 Typical Performance Characteristics 4.096V, fSMPL = 2Msps, unless otherwise noted (Note 16). Crosstalk vs Input Frequency TA = 25°C, VDD = 5V, OVDD = 2.5V, REFOUT1,2 = Output Match with Simultaneous Input Steps at CH1, CH2 CMRR vs Input Frequency –80 –124 5000 –83 OUTPUT CODE (CH1, CH2) 4000 –126 CMRR (dB) CROSSTALK (dB) –86 –128 –89 –92 –95 –98 CH2 3000 2000 1000 0 –101 –130 0 0.2 0.4 0.6 0.8 INPUT FREQUENCY (MHz) –104 1.0 0 0.5 232112 G10 Offset Error vs Temperature 1 1.5 FREQUENCY (MHz) 2 2.5 REFOUT (ppm, NORMALIZED TO 20°C) CH1 CH2 0 –0.10 –0.20 GAIN ERROR (LSB) LSB 0.10 –0.30 0.05 0 –0.05 –0.40 –0.50 –50 –25 0 25 50 –0.10 –40 75 100 125 150 TEMPERATURE (°C) –25 0 25 50 75 TEMPERATURE (°C) 232112 G13 Reference Current vs Temperature, VREF = 4.096V 200 300 TIME (ns) 400 500 232112 G12 200 0.10 0.20 100 REFOUT1,2 Output vs Temperature 0.15 0.30 0 232112 G11 0.40 0.350 –1000 Gain Error vs Temperature 0.50 CH1 100 125 100 0 4.096V –100 –200 2.048V –300 –400 –500 –50 232112 G14 Supply Current vs Sample Frequency 8 12.0 0 50 100 TEMPERATURE (°C) 150 232112 G15 OVDD Current vs SCK Frequency, CLOAD = 10pF 0.345 0.340 11.0 OVDD CURRENT (mA) SUPPLY CURRENT (mA) REFERENCE CURRENT (mA) 11.5 10.5 10.0 9.5 9.0 6 4 2 8.5 0.335 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 8 100 120 232112 G16 8.0 0 0.5 1 1.5 SAMPLE RATE (Msps) 2 232112 G17 0 0 10 20 30 40 50 60 70 80 90 100 110 SCK FREQUENCY (MHz) 232112 G18 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Pin Functions VDD (Pins 1, 8): Power Supply. Bypass VDD to GND with a 10µF ceramic and a 0.1µF ceramic close to the part. The VDD pins should be shorted together and driven from the same supply. AIN2+, AIN2– (Pins 2, 3): Analog Differential Input Pins. Full-scale range (AIN2+ – AIN2–) is ±REFOUT2 voltage. These pins can be driven from VDD to GND. GND (Pins 4, 5, 10, 29): Ground. These pins and exposed pad (Pin 29) must be tied directly to a solid ground plane. AIN1–, AIN1+ (Pins 6, 7): Analog Differential Input Pins. Full-scale range (AIN1+ – AIN1–) is ±REFOUT1 voltage. These pins can be driven from VDD to GND. CNV (Pin 9): Convert Input. This pin, when high, defines the sampling phase. When this pin is driven low, the conversion phase is initiated and output data is clocked out. This input pin is a TTL-style input typically driven at OVDD levels with a low jitter pulse, but it is bound to VDD levels. This pin is unaffected by the CMOS/LVDS pin. REFRTN1 (Pin 11): Reference Buffer 1 Output Return. Bypass REFRTN1 to REFOUT1. Do not tie the REFRTN1 pin to the ground plane. REFOUT1 (Pin 12): Reference Buffer 1 Output. An onboard buffer nominally outputs 4.096V to this pin. This pin is referred to REFRTN1 and should be decoupled closely to the pin (no vias) with a 0.1µF (X7R, 0402 size) capacitor and a 10μF (X5R, 0805 size) ceramic capacitor in parallel. The internal buffer driving this pin may be disabled by grounding the REFINT pin. If the buffer is disabled, an external reference may drive this pin in the range of 1.25V to 5V. VBYP1 (Pin 13): Bypass this internally supplied pin to ground with a 1µF ceramic capacitor. The nominal output voltage on this pin is 1.6V. OVDD (Pin 14): I/O Interface Digital Power. The range of OVDD is 1.71V to 2.5V. This supply is nominally set to the same supply as the host interface (CMOS: 1.8V or 2.5V, LVDS: 2.5V). Bypass OVDD to OGND with a 0.1μF capacitor. SDO1+, SDO1– (Pins 15, 16): Channel 1 Serial Data Output. The conversion result is shifted MSB first on each falling edge of SCK. In CMOS mode, the result is output on SDO1+. The logic level is determined by OVDD. Do not connect SDO1–. In LVDS mode, the result is output differentially on SDO1+ and SDO1–. These pins must be differentially terminated by an external 100Ω resistor at the receiver (FPGA). CLKOUT +, CLKOUT – (Pins 17, 18): Serial Data Clock Output. CLKOUT provides a skew-matched clock to latch the SDO output at the receiver. In CMOS mode, the skewmatched clock is output on CLKOUT+. The logic level is determined by OVDD. Do not connect CLKOUT–. For low throughput applications using SCK to latch the SDO output, CLKOUT+ can be disabled by tying CLKOUT– to OVDD. In LVDS mode, the skew-matched clock is output differentially on CLKOUT+ and CLKOUT–. These pins must be differentially terminated by an external 100Ω resistor at the receiver (FPGA). SDO2+, SDO2– (Pins 19, 20): Channel 2 Serial Data Output. The conversion result is shifted MSB first on each falling edge of SCK. In CMOS mode, the result is output on SDO2+. The logic level is determined by OVDD. Do not connect SDO2–. In LVDS mode, the result is output differentially on SDO2+ and SDO2–. These pins must be differentially terminated by an external 100Ω resistor at the receiver (FPGA). SCK+, SCK– (Pins 21, 22): Serial Data Clock Input. The falling edge of this clock shifts the conversion result MSB first onto the SDO pins. In CMOS mode, drive SCK+ with a single-ended clock. The logic level is determined by OVDD. Do not connect SCK–. In LVDS mode, drive SCK+ and SCK– with a differential clock. These pins must be differentially terminated by an external 100Ω resistor at the receiver (ADC). OGND (Pin 23): I/O Ground. This ground must be tied to the ground plane at a single point. OVDD is bypassed to this pin. VBYP2 (Pin 24): Bypass this internally supplied pin to ground with a 1µF ceramic capacitor. The nominal output voltage on this pin is 1.6V 232112fa For more information www.linear.com/LTC2321-12 9 LTC2321-12 Pin Functions CMOS/LVDS (Pin 25): I/O Mode Select. Ground this pin to enable CMOS mode, tie to OVDD to enable LVDS mode. Float this pin to enable low power LVDS mode. REFRTN2 (Pin 27): Reference Buffer 2 Output Return. Bypass REFRTN2 to REFOUT2. Do not tie the REFRTN2 pin to the ground plane. REFOUT2 (Pin 26): Reference Buffer 2 Output. An onboard buffer nominally outputs 4.096V to this pin. This pin is referred to REFRTN2 and should be decoupled closely to the pin (no vias) with a 0.1µF (X7R, 0402 size) capacitor and a 10μF (X5R, 0805 size) ceramic capacitor in parallel. The internal buffer driving this pin may be disabled by grounding the REFINT pin. If the buffer is disabled, an external reference may drive this pin in the range of 1.25V to VDD. REFINT (Pin 28): Reference Buffer Output Enable. Tie to VDD when using the internal reference. Tie to ground to disable the internal REFOUT1 and REFOUT2 buffers for use with external voltage references. This pin has a 500k internal pull-up to VDD. Exposed Pad (Pin 29): Ground. Solder this pad to ground. Functional Block Diagram VDD 1,8 7 6 AIN1+ AIN1– VBYP1 13 LDO + 12-BIT + SIGN SAR ADC S/H – 28 REFINT REFOUT1 12 LVDS/CMOS THREE-STATE SERIAL OUTPUT 1.2V REF 26 9 TIMING CONTROL LOGIC OUTPUT CLOCK DRIVER LVDS/CMOS RECEIVERS 2 3 AIN2– VDD 1,8 15 16 OVDD 14 G CNV AIN2+ SDO1– GND 4, 5, 10, 29 G REFOUT2 SDO1+ + 12-BIT + SIGN SAR ADC S/H – LVDS/CMOS THREE-STATE SERIAL OUTPUT LDO CLKOUT+ CLKOUT– SCK+ SCK – SDO2+ SDO2 – 17 18 21 22 19 20 VBYP2 24 232112 BD 10 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Timing Diagram ACQUISITION CONVERSION READOUT CNV 1 SCK HI-Z B12 SDO 1 CLKOUT 2 3 B11 2 4 B10 3 5 B9 4 6 10 B8 5 11 B3 6 SERIAL DATA BITS B[12:0] CORRESPOND TO CURRENT CONVERSION 10 12 B2 11 13 B1 12 B0 HI-Z 13 232112 TD Applications Information OVERVIEW CONVERTER OPERATION The LTC2321-12 is a low noise, high speed 12-bit + sign dual successive approximation register (SAR) ADC with differential inputs and wide input common mode range. The flexible analog inputs support fully differential, pseudodifferential bipolar and pseudo-differential unipolar drive without requiring any hardware configuration. The MSB of the 12-bit + sign two’s complement output indicates the sign of the differential analog input voltage. The LTC2321-12 operates in two phases. During the acquisition phase, the sample capacitor is connected to the analog input pins AIN+ and AIN – to sample the differential analog input voltage, as shown in Figure 3. A falling edge on the CNV pin initiates a conversion. During the conversion phase, the 13-bit CDAC is sequenced through a successive approximation algorithm for each input SCK pulse, effectively comparing the sampled input with binary-weighted fractions of the reference voltage (e.g., VREFOUT/2, VREFOUT/4 … VREFOUT/4096) using a differential comparator. At the end of conversion, a CDAC output approximates the sampled analog input. The ADC control logic then prepares the 13-bit digital output code for serial transfer. The ADC’s transfer function provides 13-bits of resolution across the full-scale span of 2 • VREF1,2, as shown in Figure 2. If the analog input spans less than this full-scale, such as in the case of pseudo-differential drive, the ADC provides 12-bits of resolution across this reduced span, with the additional benefit of digitizing over- and underrange conditions, as shown in Table 1. This unique feature is particularly useful in control loop applications. TRANSFER FUNCTION The LTC2321-12 digitizes the full-scale voltage of 2 • REFOUT1,2 into 213 levels, resulting in a 13-bit resolution size of 1mV with REFBUF = 4.096V. The ideal transfer function is shown in Figure 2. The output data is in 2’s compliment format. When driven by fully differential inputs, the transfer function spans 213 codes. When driven by pseudo differential inputs, the transfer function spans 212 codes. 232112fa For more information www.linear.com/LTC2321-12 11 LTC2321-12 OUTPUT CODE (TWO’S COMPLEMENT) Applications Information VDD 0 1111 1111 1111 RON 15Ω 0 1111 1111 1110 AIN1+ CIN 10pF 0 0000 0000 0001 0 0000 0000 0000 1 1111 1111 1111 BIAS VOLTAGE VDD 1LSB = 2 • REFOUT 8192 1 0000 0000 0001 1 0000 0000 0000 –REFOUT –1 0 1 LSB LSB INPUT VOLTAGE (V) AIN1– RON 15Ω CIN 10pF 232112 F03 REFOUT – 1LSB 232112 F02 Figure 2. LTC2321-12 Transfer Function Figure 3. The Equivalent Circuit for the Differential Analog Input of the LTC2321-12 Single-Ended Signals Analog Input The differential inputs of the LTC2321-12 provide great flexibility to convert a wide variety of analog signals with no configuration required. The LTC2321-12 digitizes the difference voltage between the AIN+ and AIN – pins while supporting a wide common mode input range. The analog input signals can have an arbitrary relationship to each other, provided that they remain between VDD and GND. The LTC2321-12 can also digitize more limited classes of analog input signals such as pseudo-differential unipolar/ bipolar and fully differential with no configuration required. The analog inputs of the LTC2321-12 can be modeled by the equivalent circuit shown in Figure 3. The back-to-back diodes at the inputs form clamps that provide ESD protection. In the acquisition phase, 10pF (CIN) from the sampling capacitor in series with approximately 15Ω (RON) from the on-resistance of the sampling switch is connected to the input. Any unwanted signal that is common to both inputs will be reduced by the common mode rejection of the ADC sampler. The inputs of the ADC core draw a small current spike while charging the CIN capacitors during acquisition. Single-ended signals can be directly digitized by the LTC2321-12. These signals should be sensed pseudodifferentially for improved common mode rejection. By connecting the reference signal (e.g., ground sense) of the main analog signal to the other AIN pin, any noise or disturbance common to the two signals will be rejected by the high CMRR of the ADC. The LTC2321-12 flexibility handles both pseudo-differential unipolar and bipolar signals, with no configuration required. The wide common mode input range relaxes the accuracy requirements of any signal conditioning circuits prior to the analog inputs. Pseudo-Differential Bipolar Input Range The pseudo-differential bipolar configuration represents driving one of the analog inputs at a fixed voltage, typically VREF /2, and applying a signal to the other AIN pin. In this case the analog input swings symmetrically around the fixed input yielding bipolar two’s complement output codes with an ADC span of half of full-scale. This configuration is illustrated in Figure 4, and the corresponding transfer function in Figure 5. The fixed analog input pin need not Table 1. Code Ranges for the Analog Input Operational Modes MODE Fully Differential SPAN (VIN+ – VIN–) MIN CODE MAX CODE –REFOUT to +REFOUT 1 0000 0000 0000 0 1111 1111 1111 Pseudo Differential Bipolar –REFOUT/2 to +REFOUT/2 1 1000 0000 0000 0 0111 1111 1111 Pseudo Differential Unipolar 0 to REFOUT 0 0000 0000 0000 0 1111 1111 1111 12 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Applications Information VREF VREF LT1819 + – 0V 0V LTC2321-12 25Ω AIN1+ REFOUT1 10µF VREF VBYP1 220pF 10k VREF /2 10k + – 1µF VREF /2 25Ω AIN1– 1µF TO CONTROL LOGIC (FPGA, CPLD, DSP, ETC.) SDO1 CLKOUT SCK ONLY CHANNEL 1 SHOWN FOR CLARITY 232112 F04 Figure 4. Pseudo-Differential Bipolar Application Circuit full-scale. This configuration is illustrated in Figure 6, and the corresponding transfer function in Figure 7. If the input ADC CODE (2’s COMPLEMENT) 4095 2047 –VREF –VREF /2 VREF 0 VREF /2 VREF AIN (AIN+ – AIN–) 0V LT1818 VREF + – 0V LTC2321-12 25Ω AIN1+ REFOUT1 VBYP1 220pF –2048 –4096 DOTTED REGIONS AVAILABLE BUT UNUSED 25Ω AIN1– 232112 F05 Figure 5. Pseudo-Differential Bipolar Transfer Function be set at VREF /2, but at some point within the VDD rails allowing the alternate input to swing symmetrically around this voltage. If the input signal (AIN+ – AIN –) swings beyond ±REFOUT1,2/2, valid codes will be generated by the ADC and must be clamped by the user, if necessary. SDO1 CLKOUT SCK 1µF TO CONTROL LOGIC (FPGA, CPLD, DSP, ETC.) 232112 F06 Figure 6. Pseudo-Differential Unipolar Application Circuit ADC CODE (2’s COMPLEMENT) 4095 2047 Pseudo-Differential Unipolar Input Range The pseudo-differential unipolar configuration represents driving one of the analog inputs at ground and applying a signal to the other AIN pin. In this case, the analog input swings between ground and VREF yielding unipolar two’s complement output codes with an ADC span of half of 10µF –VREF –VREF /2 –2048 –4096 0 VREF /2 VREF AIN (AIN+ – AIN–) DOTTED REGIONS AVAILABLE BUT UNUSED 232112 F07 Figure 7. Pseudo-Differential Unipolar Transfer Function 232112fa For more information www.linear.com/LTC2321-12 13 LTC2321-12 Applications Information signal (AIN+ – AIN –) swings negative, valid codes will be generated by the ADC and must be clamped by the user, if necessary. Single-Ended-to-Differential Conversion While single-ended signals can be directly digitized as previously discussed, single-ended to differential conversion circuits may also be used when higher dynamic range is desired. By producing a differential signal at the inputs of the LTC2321-12, the signal swing presented to the ADC is maximized, thus increasing the achievable SNR. The LT®1819 high speed dual operational amplifier is recommended for performing single-ended-to-differential conversions, as shown in Figure 8. In this case, the first amplifier is configured as a unity-gain buffer and the single-ended input signal directly drives the high impedance input of this amplifier. Fully-Differential Inputs To achieve the full distortion performance of the LTC2321-12, a low distortion fully-differential signal source driven through the LT1819 configured as two unity-gain buffers, as shown in Figure 9, can be used. This circuit achieves the full data sheet THD specification of –85dB at input VREF 0V 200Ω VREF /2 + – VREF + – VREF 0V 0V VREF 0V 0V LT1819 + – VREF + – VREF 0V 0V 232112 F09 232112 F08 Figure 8. Single-Ended to Differential Driver 14 The fully-differential configuration yields an analog input span (AIN+ – AIN –) of ±REFOUT1,2. In this configuration, the input signal is driven on each AIN pin, typically at equal spans but opposite polarity. This yields a high common mode rejection on the input signals. The common mode voltage of the analog input can be anywhere within the VDD input range, but will be limited by the peak swing of the full-range input signal. For example, if the internal reference is used with VDD = 5VDC, the full-range input span will be ±4.096V. Half of the input span is typically driven on each AIN pin, yielding a signal span for each AIN pin of 4.096VP-P. This leaves ~0.9V of common mode variation tolerance. When using external references, it is possible to increase common mode tolerance by compressing the ADC full-range codes into a tighter range. For example, using an external 2.048V reference with VDD = 5V the total span would be ±2.048V and each AIN span would be limited to 2.048VP-P allowing a common mode range of ~3V. Compressing the input span would incur a SNR penalty of approximately 1dB. Input span compression may be useful if single-supply analog input drivers are used which VREF LT1819 200Ω frequencies of 500kHz and less. Data sheet typical performance curves taken at higher frequencies used a harmonic rejection filter between the ADC and the signal source to eliminate the op amp as the dominant source of distortion. Figure 9. LT1819 Buffering a Fully-Differential Signal Source 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Applications Information cannot swing rail-to-rail. The fully-differential configuration is illustrated in Figure 10, with the corresponding transfer function illustrated in Figure 11. is important even for DC inputs, because the ADC inputs draw a current spike when during acquisition. For best performance, a buffer amplifier should be used to drive the analog inputs of the LTC2321-12. The amplifier provides low output impedance to minimize gain error and allow for fast settling of the analog signal during the acquisition phase. It also provides isolation between the signal source and the ADC inputs, which draw a small current spike during acquisition. INPUT DRIVE CIRCUITS A low impedance source can directly drive the high impedance inputs of the LTC2321-12 without gain error. A high impedance source should be buffered to minimize settling time during acquisition and to optimize the distortion performance of the ADC. Minimizing settling time VREF 0V VREF LT1819 + – 0V LTC2321-12 25Ω AIN1+ VBYP1 220pF VREF 0V REFOUT1 VREF + – 0V 25Ω AIN1– SDO1 CLKOUT SCK ONLY CHANNEL 1 SHOWN FOR CLARITY 10µF 1µF TO CONTROL LOGIC (FPGA, CPLD, DSP, ETC.) 232112 F10 Figure 10. Fully-Differential Application Circuit ADC CODE (2’s COMPLEMENT) 4095 2047 –VREF –VREF /2 0 VREF /2 VREF AIN (AINn + – AINn –) –2048 –4096 232112 F11 Figure 11. Fully-Differential Transfer Function 232112fa For more information www.linear.com/LTC2321-12 15 LTC2321-12 Applications Information Input Filtering ADC REFERENCE The noise and distortion of the buffer amplifier and signal source must be considered since they add to the ADC noise and distortion. Noisy input signals should be filtered prior to the buffer amplifier input with a low bandwidth filter to minimize noise. The simple 1-pole RC lowpass filter shown in Figure 12 is sufficient for many applications. The input resistor divider network, sampling switch onresistance (RON) and the sample capacitor (CIN) form a second lowpass filter that limits the input bandwidth to the ADC core to 110MHz. A buffer amplifier with a low noise density must be selected to minimize the degradation of the SNR over this bandwidth. High quality capacitors and resistors should be used in the RC filters since these components can add distortion. NPO and silver mica type dielectric capacitors have excellent linearity. Carbon surface mount resistors can generate distortion from self heating and from damage that may occur during soldering. Metal film surface mount resistors are much less susceptible to both problems. SINGLE-ENDED INPUT SIGNAL 50Ω 3.3nF BW = 1MHz Internal Reference The LTC2321-12 has an on-chip, low noise, low drift (20ppm/°C max), temperature compensated bandgap reference. It is internally buffered and is available at REFOUT1,2 (Pins 12, 26). The reference buffer gains the internal reference voltage to 4.096V for supply voltages VDD = 5V and to 2.048V for VDD = 3.3V. Bypass REFOUT1,2 to REFRTN1,2 with the parallel combination of a 0.1µF (X7R, 0402 size) capacitor and a 10μF (X5R, 0805 size) ceramic capacitor to compensate the reference buffer and minimize noise. The 0.1µF capacitor should be as close as possible to the LTC2321-12 package to minimize wiring inductance. Tie the REFINT pin to VDD to enable the internal reference buffer. Table 2. REFOUT1,2 Sources and Ranges vs VDD VDD REFINT PIN REFOUT1,2 PIN DIFFERENTIAL SPAN 5V 5V Internal 4.096V ±4.096V 5V 0V External (1.25V to 5V) ±1.25V to ±5V 3.3V 3.3V Internal 2.048V ±2.048V 3.3V 0V External (1.25V to 3.3V) ±1.25V to ±3.3V IN+ LTC2321 IN– SINGLE-ENDED TO DIFFERENTIAL DRIVER 232112 F12 Figure 12. Input Signal Chain 16 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Applications Information External Reference The internal reference buffer can also be overdriven from 1.25V to 5V with an external reference at REFOUT1,2 as shown in Figure 13 (b and c). To do so, REFINT must be grounded to disable the reference buffer. A 55k internal resistance loads the REFOUT1,2 pins when the reference buffer is disabled. To maximize the input signal swing and corresponding SNR, the LTC6655-5 is recommended when overdriving REFOUT. The LTC6655-5 offers the same small size, accuracy, drift and extended temperature range as the LTC6655-4.096. By using a 5V reference, a higher SNR can be achieved. We recommend bypassing the LTC6655-5 with a parallel combination of a 0.1µF (X7R, 0402 size) ceramic capacitor and a 10μF ceramic capacitor (X5R, 0805 size) close to each of the REFOUT1,2 and REFRTN1,2 pins. Internal Reference Buffer Transient Response The REFOUT1,2 pins of the LTC2321-12 draw charge (QCONV) from the external bypass capacitors during each conversion cycle. If the internal reference buffer is overdriven, the external reference must provide all of this charge with a DC current equivalent to IREF = QCONV/tCYC. Thus, the DC current draw of REFOUT1,2 depends on the sampling rate and output code. In applications where a burst of samples is taken after idling for long REFINT VDD REFINT REFOUT1 3.3V TO 5V 0.1µF 10µF REFOUT1 LTC2321-12 0.1µF 5V TO 13.2V REFRTN1 0.1µF REFRTN2 0.1µF 10µF LTC6655-4.096 VIN VOUT_F SHDN VOUT_S 10µF LTC2321-12 REFRTN1 0.1µF REFRTN2 10µF REFOUT2 GND REFOUT2 GND 232112 F13b 232112 F13a (13a) LTC2321-12 Internal Reference Circuit (13b) LTC2321-12 with a Shared External Reference Circuit 5V TO 13.2V 0.1µF REFINT LTC6655-4.096 VIN VOUT_F SHDN VOUT_S REFOUT1 0.1µF 10µF REFRTN1 0.1µF 0.1µF LTC6655-2.048 VIN VOUT_F SHDN VOUT_S LTC2321-12 REFRTN2 10µF REFOUT2 GND 232112 F13c (13c) LTC2321-12 with Different External Reference Voltages Figure 13. Reference Connection 232112fa For more information www.linear.com/LTC2321-12 17 LTC2321-12 Applications Information periods, as shown in Figure 14 , IREFBUF quickly goes from approximately ~75µA to a maximum of 400µA for REFOUT = 5V at 2Msps. This step in DC current draw triggers a transient response in the external reference that must be considered since any deviation in the voltage at REFOUT will affect the accuracy of the output code. If an external reference is used to overdrive REFOUT1,2 the fast settling LTC6655 reference is recommended. CNV 232112 F14 Figure 14. CNV Waveform Showing Burst Sampling 5000 OUTPUT CODE (CH1, CH2) Fast Fourier transform (FFT) 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. The LTC2321-12 provides guaranteed tested limits for both AC distortion and noise measurements. Signal-to-Noise and Distortion Ratio (SINAD) IDLE PERIOD 4000 DYNAMIC PERFORMANCE CH1 CH2 3000 The signal-to-noise and distortion ratio (SINAD) is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components at the A/D output. The output is bandlimited to frequencies from above DC and below half the sampling frequency. Figure 16 shows that the LTC2321-12 achieves a typical SINAD of 72.8dB at a 2MHz sampling rate with a 500kHz input. 2000 Signal-to-Noise Ratio (SNR) 1000 The signal-to-noise ratio (SNR) is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components except the first five harmonics and DC. Figure 16 shows that the LTC2321-12 achieves a typical SNR of 73dB at a 2MHz sampling rate with a 500kHz input. 0 –1000 0 100 200 300 TIME (ns) 400 500 232112 F15 Figure 15. Transient Response of the LTC2321-12 AMPLITUDE (dBFS) 0 SNR = 72.9dB THD = –86.1dB –20 SINAD = 72.8dB SFDR = 89.5dB –40 –60 –80 –100 –120 –140 0 0.2 0.4 0.6 FREQUENCY (MHz) 0.8 1 232112 F16 Figure 16. 32k Point FFT of the LTC2321-12 18 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Applications Information Total Harmonic Distortion (THD) 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 (fSMPL /2). THD is expressed as: THD= 20log V22 + V32 + V42 +…+ VN2 V1 where V1 is the RMS amplitude of the fundamental frequency and V2 through VN are the amplitudes of the second through Nth harmonics. POWER CONSIDERATIONS The LTC2321-12 requires two power supplies: the 5V power supply (VDD), and the digital input/output interface power supply (OVDD). The flexible OVDD supply allows the LTC2321-12 to communicate with any digital logic operating between 1.8V and 2.5V. When using LVDS I/O, the OVDD supply must be set to 2.5V. Power Supply Sequencing The LTC2321-12 does not have any specific power supply sequencing requirements. Care should be taken to adhere to the maximum voltage relationships described in the Absolute Maximum Ratings section. The LTC232112 has a power-on-reset (POR) circuit that will reset the LTC2321-12 at initial power-up or whenever the power supply voltage drops below 2V. Once the supply voltage re-enters the nominal supply voltage range, the POR will reinitialize the ADC. No conversions should be initiated until 10ms after a POR event to ensure the reinitialization period has ended. Any conversions initiated before this time will produce invalid results. 12.0 SUPPLY CURRENT (mA) 11.5 11.0 10.5 10.0 9.5 9.0 8.5 8.0 0 0.5 1 1.5 SAMPLE RATE (Msps) 2 232112 F17 Figure 17. Power Supply Current of the LTC2321-12 Versus Sampling Rate 232112fa For more information www.linear.com/LTC2321-12 19 LTC2321-12 Applications Information TIMING AND CONTROL Nap/Sleep Modes CNV Timing Nap mode is a method to save power without sacrificing power-up delays for subsequent conversions. Sleep mode has substantial power savings, but a power-up delay is incurred to allow the reference and power systems to become valid. To enter nap mode on the LTC2321-12, the SCK signal must be held high or low and a series of two CNV pulses must be applied. This is the case for both CMOS and LVDS modes. The second rising edge of CNV initiates the nap state. The nap state will persist until either a single rising edge of SCK is applied, or further CNV pulses are applied. The SCK rising edge will put the LTC2321-12 back into the operational (full-power) state. When in nap mode, two additional pulses will put the LTC2321-12 in sleep mode. When configured for CMOS I/O operation, a single rising edge of SCK can return the LTC2321-12 into operational mode. A 10ms delay is necessary after exiting sleep mode to allow the reference buffer to recharge the external filter capacitor. In LVDS mode, exit sleep mode by supplying a fifth CNV pulse. The fifth pulse will return the LTC2321-12 to operational mode, and further SCK pulses will keep the part from re-entering nap and sleep modes. The fifth SCK pulse also works in CMOS mode as a method to exit sleep. In the absence of SCK pulses, repetitive CNV pulses will cycle the LTC2321-12 between operational, nap and sleep modes indefinitely. The LTC2321-12 sampling and conversion is controlled by CNV. A rising edge on CNV will start sampling and the falling edge starts the conversion and readout process. The conversion process is timed by the SCK input clock. For optimum performance, CNV should be driven by a clean low jitter signal. The Typical Application at the back of the data sheet illustrates a recommended implementation to reduce the relatively large jitter from an FPGA CNV pulse source. Note the low jitter input clock times the falling edge of the CNV signal. The rising edge jitter of CNV is much less critical to performance. The typical pulse width of the CNV signal is 30ns at a 2Msps conversion rate. SCK Serial Data Clock Input The falling edge of this clock shifts the conversion result MSB first onto the SDO pins. A 64MHz external clock must be applied at the SCK pin to achieve 2Msps throughput. CLKOUT Serial Data Clock Output The CLKOUT output provides a skew-matched clock to latch the SDO output at the receiver. The timing skew of the CLKOUT and SDO outputs are matched. For high throughput applications, using CLKOUT instead of SCK to capture the SDO output eases timing requirements at the receiver. For low throughput applications, CLKOUT+ can be disabled by tying CLKOUT– to OVDD. CNV 1 Refer to the timing diagrams in Figure 18, Figure 19, Figure 20 and Figure 21 for more detailed timing information about sleep and nap modes. 2 FULL POWER MODE NAP MODE SCK SDO1 SDO2 HOLD STATIC HIGH OR LOW WAKE ON 1ST SCK EDGE Z Z 232112 F18 Figure 18. CMOS and LVDS Mode NAP and WAKE Using SCK 20 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Applications Information REFOUT1 REFOUT2 REFOUT RECOVERY 4.096V 4.096V tWAKE CNV 1 2 3 4 NAP MODE SCK SLEEP MODE FULL POWER MODE HOLD STATIC HIGH OR LOW WAKE ON 1ST SCK EDGE SDO1 SDO2 Z Z Z Z 232112 F19 Figure 19. CMOS Mode SLEEP and WAKE Using SCK REFOUT1 REFOUT2 REFOUT RECOVERY 4.096V 4.096V tWAKE CNV 1 2 3 4 NAP MODE SCK WAKE ON 5TH CSB EDGE 5 SLEEP MODE FULL POWER MODE HOLD STATIC HIGH OR LOW SDO1 SDO2 Z Z Z Z Z 232112 F20 Figure 20. LVDS and CMOS Mode SLEEP and WAKE Using CNV tDSCKHCNVH CNV tSCKL 1 SCK 3 4 5 tSCK 6 10 11 12 13 tDCNVSDOV HI-Z B12 SDO B11 B10 B9 B8 tDCLKOUTSDOV 1 CLKOUT tCNVH 2 tSCKH 2 3 4 tCONV B3 B2 B1 B0 HI-Z tHSDO 5 6 tREADOUT 10 11 12 13 tDCNVSDOZ tCYC SERIAL DATA BITS B[12:0] CORRESPOND TO CURRENT CONVERSION tDSCKCLKOUT IS THE DELAY FROM SCK↓ TO CLKOUT↓ 232112 F21 Figure 21. LTC2321-12 Timing Diagram 232112fa For more information www.linear.com/LTC2321-12 21 LTC2321-12 Applications Information Digital Interface skew of the CLKOUT and SDO outputs are matched. For high throughput applications, using CLKOUT instead of SCK to capture the SDO output eases timing requirements at the receiver. The LTC2321-12 features a serial digital interface that is simple and straight forward to use. The flexible OVDD supply allows the LTC2321-12 to communicate with any digital logic operating between 1.8V and 2.5V. A 64MHz external clock must be applied at the SCK pin to achieve 2Msps throughput. In CMOS mode, use the SDO1+, SDO2+ and CLKOUT+ pins as outputs. Use the SCK+ pin as an input. Do not connect the SDO1–, SDO2–, SCK– and CLKOUT– pins, as they each have internal pull-down circuitry to OGND. In addition to a standard CMOS SPI interface, the LTC232112 provides an optional LVDS SPI interface to support low noise digital design. The CMOS/LVDS pin is used to select the digital interface mode. In LVDS mode, use the SDO1+/SDO1–, SDO2+/SDO2– and CLKOUT+/CLKOUT– pins as differential outputs. These pins must be differentially terminated by an external 100Ω resistor at the receiver (FPGA). The SCK+/SCK– pins are differential inputs and must be terminated differentially by an external 100Ω resistor at the receiver (ADC). The falling edge of SCK outputs the conversion result MSB first on the SDO pins. CLKOUT provides a skew-matched clock to latch the SDO output at the receiver. The timing LTC2321-12 2.5V FPGA OR DSP OVDD SDO1+ SDO1– 100Ω + – 100Ω + – CLKOUT+ CLKOUT – SCK+ 2.5V + – 100Ω CMOS/LVDS SCK– SDO2+ 100Ω SDO2– + – CNV 232112 F22 Figure 22. LTC2321 Using the LVDS Interface 22 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Applications Information BOARD LAYOUT Recommended Layout To obtain the best performance from the LTC2321-12, a printed circuit board is recommended. Layout for the printed circuit board (PCB) should ensure the digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital clocks or signals adjacent to analog signals or underneath the ADC. The following is an example of a recommended PCB layout. A single solid ground plane is used. Bypass capacitors to the supplies are placed as close as possible to the supply pins. Low impedance common returns for these bypass capacitors are essential to the low noise operation of the ADC. The analog input traces are screened by ground. For more details and information, refer to the DC1996, the evaluation kit for the LTC2321-12. Figure 1. Layer 1, Top Layer Figure 3. Layer 3, Power Plane Figure 2. Layer 2, Ground Plane Figure 4. Layer 4, Bottom Layer 232112fa For more information www.linear.com/LTC2321-12 23 LTC2321-12 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UFD Package 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 ±0.05 4.50 ±0.05 3.10 ±0.05 2.50 REF 2.65 ±0.05 3.65 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 3.50 REF 4.10 ±0.05 5.50 ±0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) 0.75 ±0.05 R = 0.05 TYP PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 2.50 REF R = 0.115 TYP 27 28 0.40 ±0.10 PIN 1 TOP MARK (NOTE 6) 1 2 5.00 ±0.10 (2 SIDES) 3.50 REF 3.65 ±0.10 2.65 ±0.10 (UFD28) QFN 0506 REV B 0.200 REF 0.00 – 0.05 0.25 ±0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X). 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 24 232112fa For more information www.linear.com/LTC2321-12 LTC2321-12 Revision History REV DATE DESCRIPTION A 10/14 Updated Timing Characteristics and Figure 21 PAGE NUMBER 6, 21 232112fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of itsinformation circuits as described herein will not infringe on existing patent rights. For more www.linear.com/LTC2321-12 25 LTC2321-12 Typical Application Low Jitter Clock Timing with RF Sine Generator Using Clock Squaring/Level-Shifting Circuit and Retiming Flip-Flop VCC 0.1µF 50Ω 1k NC7SVUO4P5X MASTER_CLOCK VCC 1k D PRE NC7SV74KBX Q CLR CONV CONV ENABLE LTC2321-12 CNV SCK CLKOUT GND CMOS/LVDS SDO1 SDO2 CONTROL LOGIC (FPGA, CPLD, DSP, ETC.) 10Ω 10Ω 10Ω NC7SVU04P5X (× 3) 232112 TA02 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC2321-16/LTC2321-14 16-Bit/14-Bit, 2Msps Simultaneous Sampling ADC 3.3V/5V Supply Differential Input Common Mode Range, 4mm × 5mm QFN-28 Package LTC2314-14 14-Bit, 4.5Msps Serial ADC 3V/5V Supply, 18mW/31mW, 20ppm/°C Max Internal Reference, Unipolar Inputs, 8-Lead TSOT-23 Package ADCs LTC2370-16/LTC2368-16/ 16-Bit, 2Msps/1Msps/500ksps/250ksps Serial, LTC2367-16/LTC2364-16 Low Power ADC 2.5V Supply, Pseudo-Differential Unipolar Input, 94dB SNR, 5V Input Range, DGC, Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages LTC2380-16/LTC2378-16/ 16-Bit, 2Msps/1Msps/500ksps/250ksps Serial, LTC2377-16/LTC2376-16 Low Power ADC 2.5V Supply, Differential Input, 96.2dB SNR, ±5V Input Range, DGC, PinCompatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages DACs LTC2632 Dual 12-/10-/8-Bit, SPI VOUT DACs with Internal Reference 2.7V to 5.5V Supply Range, 10ppm/°C Reference, External REF Mode, Rail-to-Rail Output, 8-Pin ThinSOT™ Package LTC2602/LTC2612/ LTC2622 Dual 16-/14-/12-Bit SPI VOUT DACs with External Reference 300μA per DAC, 2.5V to 5.5V Supply Range, Rail-to-Rail Output, 8-Lead MSOP Package LTC6655 Precision Low Drift, Low Noise Buffered Reference 5V/4.096V/3.3V/3V/2.5V/2.048V/1.25V, 5ppm/°C, 0.25ppm Peak-to-Peak Noise, MSOP-8 Package LTC6652 Precision Low Drift, Low Noise Buffered Reference 5V/4.096V/3.3V/3V/2.5V/2.048V/1.25V, 5ppm/°C, 2.1ppm Peak-to-Peak Noise, MSOP-8 Package LT1818/LT1819 400MHz, 2500V/µs, 9mA Single/Dual Operational Amplifiers –85dBc Distortion at 5MHz, 6nV/√Hz Input Noise Voltage, 9mA Supply Current, Unity-Gain Stable LT1806 325MHz, Single, Rail-to-Rail Input and Output, Low –80dBc Distortion at 5MHz, 3.5nV/√Hz Input Noise Voltage, Distortion, Low Noise Precision Op Amps 9mA Supply Current, Unity-Gain Stable LT6200 165MHz, Rail-to-Rail Input and Output, 0.95nV/√Hz Low Noise, Low Distortion, Unity-Gain Stable Low Noise, Op Amp Family References Amplifiers 26 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC2321-12 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC2321-12 232112fa LT 1014 REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2014