LTC2380-24 24-Bit, 1.5Msps/2Msps, Low Power SAR ADC with Integrated Digital Filter DESCRIPTION FEATURES Guaranteed 24-Bits No Missing Codes nn ±0.5ppm INL (Typ) nn Integrated Digital Filter with Real-Time Averaging nn Low Power: 28mW at 2Msps nn 100dB SNR (Typ) at 1.5Msps nn 145dB Dynamic Range (Typ) at 30.5sps nn –117dB THD (Typ) at f = 2kHz IN nn 50Hz/60Hz Rejection nn Digital Gain Compression (DGC) nn Guaranteed Operation to 85°C nn Single 2.5V Supply nn Fully Differential Input Range Up to ±5V nn 1.8V to 5V SPI-Compatible Serial I/O with DaisyChain Mode nn 16-Lead MSOP and 4mm × 3mm DFN Packages The LTC®2380-24 is a low noise, low power, high speed 24-bit successive approximation register (SAR) ADC with an integrated digital averaging filter. Operating from a 2.5V supply, the LTC2380-24 has a ±VREF fully differential input range with VREF ranging from 2.5V to 5.1V. The LTC238024 consumes only 28mW and achieves ±3.5ppm INL maximum and no missing codes at 24 bits. nn The LTC2380-24 has an easy to use integrated digital averaging filter that can average 1 to 65536 conversion results real-time, dramatically improving dynamic range from 101dB at 1.5Msps to 145dB at 30.5sps. No separate programming interface or configuration register is required. The high speed SPI-compatible serial interface supports 1.8V, 2.5V, 3.3V and 5V logic while also featuring a daisychain mode. The LTC2380-24 automatically powers down between conversions, reducing power dissipation at lower sampling rates. APPLICATIONS Seismology Energy Exploration nn Medical Imaging nn High Speed Data Acquisition nn Industrial Process Control nn ATE nn L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and SoftSpan is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 7705765, 7961132, 8319673, 8810443 and Patents pending. nn TYPICAL APPLICATION Integral Nonlinearity vs Output Code 1.8V TO 5V 10µF VREF 0V VREF 0V + 10Ω 6800pF – 10Ω OVDD VDD IN+ 3300pF LTC2380-24 IN– 6800pF REF 2.5V TO 5.1V 2.0 0.1µF GND CHAIN RDL/SDI SDO SCK BUSY CNV REF/DGC SAMPLE CLOCK VREF 238024 TA01 47µF (X7R, 1210 SIZE) INL ERROR (ppm) 2.5V 3.0 1.0 0 –1.0 –2.0 –3.0 0 4194304 8388608 12582912 16777216 OUTPUT CODE 3681 TA01b 238024f For more information www.linear.com/LTC2380-24 1 LTC2380-24 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) Supply Voltage (VDD)................................................2.8V Supply Voltage (OVDD).................................................6V Reference Input (REF)..................................................6V Analog Input Voltage (Note 3) IN+, IN–..............................(GND – 0.3V) to (REF + 0.3V) REF/DGC Input (Note 3).....(GND – 0.3V) to (REF + 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............................................... 500mW Operating Temperature Range LTC2380C................................................. 0°C to 70°C LTC2380I..............................................–40°C to 85°C Storage Temperature Range................... –65°C to 150°C PIN CONFIGURATION TOP VIEW CHAIN 1 VDD 2 GND 3 + 4 IN– 5 GND 6 REF 7 REF/DGC 8 IN 16 GND 15 OVDD 17 GND TOP VIEW CHAIN VDD GND IN+ IN– GND REF REF/DGC 14 SDO 13 SCK 12 RDL/SDI 11 BUSY 10 GND 9 CNV 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 GND OVDD SDO SCK RDL/SDI BUSY GND CNV MS PACKAGE 16-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 110°C/W DE PACKAGE 16-LEAD (4mm × 3mm) PLASTIC DFN TJMAX = 150°C, θJA = 40°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2380CMS-24#PBF LTC2380CMS-24#TRPBF 238024 16-Lead Plastic MSOP 0°C to 70°C LTC2380IMS-24#PBF LTC2380IMS-24#TRPBF 238024 16-Lead Plastic MSOP –40°C to 85°C LTC2380CDE-24#PBF LTC2380CDE-24#TRPBF 23804 16-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C LTC2380IDE-24#PBF LTC2380IDE-24#TRPBF 23804 16-Lead (4mm × 3mm) Plastic DFN –40°C to 85°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/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 238024f 2 For more information www.linear.com/LTC2380-24 LTC2380-24 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 VIN+ Absolute Input Range (IN+) (Note 5) – Absolute Input Range (IN–) VIN+ – VIN– Input Differential Voltage Range VCM Common Mode Input Range VIN MIN TYP MAX UNITS l −0.1 VREF + 0.1 V (Note 5) l −0.1 VREF + 0.1 V VIN = VIN+ – VIN– l −VREF VREF V l −VREF/2 – 0.1 VREF/2 + 0.1 V VREF/2 IIN Analog Input Leakage Current 0.01 μA CIN Analog Input Capacitance Sample Mode Hold Mode 45 5 pF pF CMRR Input Common Mode Rejection Ratio fIN = 1MHz 86 dB CONVERTER CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4) SYMBOL N PARAMETER CONDITIONS MIN TYP MAX UNITS Resolution l 24 Bits No Missing Codes l 24 Bits l 1 Number of Averages 65536 Transition Noise N = 1, fSMPL = 1.5Msps N = 16, fSMPL = 2Msps N = 1024, fSMPL = 2Msps N = 16384, fSMPL = 2Msps l l l l 55.7 13.6 1.75 0.55 INL Integral Linearity Error N = 1, fSMPL = 1.5Msps (Note 6) N = 1, fSMPL = 1.5Msps REF/DGC = GND (Note 6) N = 4, fSMPL = 2Msps (Note 6) l l l –3.5 –3.5 –3.5 ±0.5 ±0.5 ±0.5 3.5 3.5 3.5 ppm ppm ppm DNL Differential Linearity Error (Note 7) l –0.5 ±0.2 0.5 LSB ZSE Zero-Scale Error (Note 8) l −10 0 10 Zero-Scale Error Drift FSE Full-Scale Error LSBRMS LSBRMS LSBRMS LSBRMS ppm ±7 (Note 8) l −100 ppb/°C ±10 Full-Scale Error Drift 100 ±0.05 ppm 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, 9) SYMBOL PARAMETER CONDITIONS DR Dynamic Range IN+ = IN– = VCM, VREF = 5V, N = 1, fSMPL = 1.5Msps IN+ = IN– = VCM, VREF = 5V, N = 16, fSMPL = 2Msps IN+ = IN– = VCM, VREF = 5V, N = 1024, fSMPL = 2Msps IN+ = IN– = VCM, VREF = 5V, N = 16384, fSMPL = 2Msps IN+ = IN– = VCM, VREF = 5V, N = 65536, fSMPL = 2Msps SINAD Signal-to-(Noise + Distortion) Ratio fIN = 2kHz, VREF = 5V Signal-to-Noise Ratio fIN = 2kHz, VREF = 5V, N = 1, fSMPL = 1.5Msps fIN = 2kHz, VREF = 5V, REF/DGC = GND, N = 1, fSMPL = 1.5Msps fIN = 2kHz, VREF = 2.5V, N = 1, fSMPL = 1.5Msps fIN = 2kHz, VREF = 5V, N = 16, AIN = –20dBFS, fSMPL = 2Msps fIN = 100Hz, VREF = 5V, N = 1024, AIN = –20dBFS, fSMPL = 2Msps l l l l Total Harmonic Distortion l l l SNR THD fIN = 2kHz, VREF = 5V, N = 1, fSMPL = 1.5Msps fIN = 2kHz, VREF = 5V, REF/DGC = GND, N = 1, fSMPL = 1.5Msps fIN = 2kHz, VREF = 2.5V, N = 1, fSMPL = 1.5Msps fIN = 2kHz, VREF = 5V, N = 16, AIN = –20dBFS, fSMPL = 2Msps fIN = 100Hz, VREF = 5V, N = 1024, AIN = –20dBFS, fSMPL = 2Msps MIN TYP MAX UNITS 101 113 131 141 145 dB dB dB dB dB 97.5 100 dB 97.5 95.5 92.5 100 98 95 112 130 dB dB dB dB dB –117 –119 –117 –140 –140 –114 –114 –113 dB dB dB dB dB 238024f For more information www.linear.com/LTC2380-24 3 LTC2380-24 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, 9) SYMBOL PARAMETER CONDITIONS SFDR fIN = 2kHz, VREF = 5V MIN TYP 114 120 dB –3dB Input Linear Bandwidth 34 MHz Aperture Delay 500 Aperture Jitter 4 Spurious Free Dynamic Range Transient Response l Full–Scale Step MAX UNITS ps psRMS 115 ns REFERENCE INPUT 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 VREF Reference Voltage (Note 5) l IREF Reference Input Current (Note 10) l VIHDGC High Level Input Voltage REF/DGC Pin l VILDGC Low Level Input Voltage REF/DGC Pin l TYP 2.5 1.9 MAX UNITS 5.1 V 2.1 mA 0.8VREF V 0.2VREF V 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 VIH High Level Input Voltage l VIL Low Level Input Voltage l IIN Digital Input Current CIN Digital Input Capacitance CONDITIONS VIN = 0V to OVDD MIN l TYP MAX UNITS 0.8 • OVDD V –10 0.2 • OVDD V 10 μA 5 pF VOH High Level Output Voltage IO = –500µA l OVDD – 0.2 VOL Low Level Output Voltage IO = 500µA l V IOZ Hi-Z Output Leakage Current VOUT = 0V to OVDD l ISOURCE Output Source Current VOUT = 0V –10 mA ISINK Output Sink Current VOUT = OVDD 10 mA –10 0.2 V 10 µA 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 CONDITIONS OVDD Supply Voltage IVDD IOVDD IPD Supply Current Supply Current Power Down Mode N = 4, fSMPL = 2Msps N = 4, fSMPL = 2Msps (CL = 20pF) Conversion Done (IVDD + IOVDD + IREF) PD Power Dissipation Power Down Mode N = 4, fSMPL = 2Msps Conversion Done (IVDD + IOVDD + IREF) MIN TYP MAX UNITS l 2.375 2.5 2.625 V l 1.71 l l 5.25 V 11.2 0.4 1 13 90 mA mA μA 28 2.5 32.5 225 mW μW 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 N≥4 fODR Output Data Rate MIN TYP MAX UNITS l 2 Msps l 1.5 Msps 238024f 4 For more information www.linear.com/LTC2380-24 LTC2380-24 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 tCONV Conversion Time tACQ Acquisition Time CONDITIONS MIN tACQ = tCYC – tCONV – tBUSYLH (Note 7) l 343 l 115 TYP MAX UNITS 392 ns ns tCYC Time Between Conversions l 500 ns tCNVH CNV High Time l 20 ns tCNVL 20 Minimum Low Time for CNV (Note 11) l tBUSYLH CNV↑ to BUSY↑ Delay CL = 20pF l ns tQUIET SCK Quiet Time from CNV↑ (Note 7) l 10 ns tSCK SCK Period (Notes 11, 12) l 10 ns tSCKH SCK High Time l 4 ns tSCKL SCK Low Time l 4 ns tSSDISCK 13 ns SDI Setup Time From SCK↑ (Note 11) l 4 ns tHSDISCK SDI Hold Time From SCK↑ (Note 11) l 1 ns tSCKCH SCK Period in Chain Mode tSCKCH = tSSDISCK + tDSDO (Note 11) l 13.5 ns tDSDO SDO Data Valid Delay from SCK↑ CL = 20pF, OVDD = 5.25V CL = 20pF, OVDD = 2.5V CL = 20pF, OVDD = 1.71V l l l SDO Data Remains Valid Delay from SCK↑ CL = 20pF (Note 7) tDSDOBUSYL SDO Data Valid Delay from BUSY↓ CL = 20pF (Note 7) tEN (Note 11) Bus Enable Time After RDL↓ l tDIS tHSDO Bus Relinquish Time After RDL↑ (Note 11) 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 REF or OVDD, they will be clamped by internal diodes. This product can handle input currents up to 100mA below ground or above REF or OVDD without latchup. Note 4: VDD = 2.5V, OVDD = 2.5V, REF = 5V, VCM = 2.5V, fSMPL = 1.5MHz, REF/DGC = VREF, N = 1. 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. 7.5 8 9.5 1 ns ns ns ns l 5 ns l 16 ns l 13 ns Note 7: Guaranteed by design, not subject to test. Note 8: Bipolar zero-scale error is the offset voltage measured from –0.5LSB when the output code flickers between 0000 0000 0000 0000 0000 0000 and 1111 1111 1111 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. Note 9: All specifications in dB are referred to a full-scale ±5V input with a 5V reference voltage. Note 10: fSMPL = 2MHz, IREF varies proportionally with sample rate. Note 11: Parameter tested and guaranteed at OVDD = 1.71V, OVDD = 2.5V and OVDD = 5.25V. Note 12: tSCK of 10ns maximum allows a shift clock frequency up to 100MHz for rising edge capture. 0.8 • OVDD tWIDTH 0.2 • OVDD tDELAY tDELAY 0.8 • OVDD 0.8 • OVDD 0.2 • OVDD 0.2 • OVDD 50% 50% 238024 F01 Figure 1. Voltage Levels for Timing Specifications 238024f For more information www.linear.com/LTC2380-24 5 LTC2380-24 TYPICAL PERFORMANCE CHARACTERISTICS REF = 5V, fSMPL = 1.5Msps, N = 1, unless otherwise noted. Integral Nonlinearity vs Output Code TA = 25°C, VDD = 2.5V, OVDD = 2.5V, VCM = 2.5V, Differential Nonlinearity vs Output Code 3.0 DC Histogram, N = 1 1.0 10000 σ = 55.7 0.8 0.6 0 –1.0 8000 0.4 0.2 6000 COUNTS 1.0 DNL ERROR (LSB) INL ERROR (ppm) 2.0 –0.0 –0.2 4000 –0.4 –0.6 –2.0 2000 –0.8 –3.0 0 4194304 –1.0 8388608 12582912 16777216 OUTPUT CODE 0 4194304 238024 G01 DC Histogram, N = 16, fSMPL = 2Msps 10000 σ = 13.6 DC Histogram, N = 1024, fSMPL = 2Msps 6000 6000 6000 4000 COUNTS 8000 4000 2000 2000 –100 0 CODE 100 200 0 300 –8 –6 –4 –2 0 2 CODE 4 0 σ = 0.33 AMPLITUDE (dBFS) 4000 2000 –6 –4 –2 0 2 CODE 4 6 8 238024 G07 –60 –80 –100 –120 0 DC Histogram, N = 16384, fSMPL = 2Msps σ = 0.55 –8 –6 –4 –2 0 2 CODE 4 6 –80 –100 –120 –160 300 450 FREQUENCY (kHz) 600 750 238024 G08 SNR = 112.4dB –60 –160 150 128k Point FFT fSMPL = 2Msps, fIN = 2kHz, N = 16 –40 –140 0 8 –20 –140 –180 300 238024 G06 SNR = 100.3dB THD = –117.3dB SINAD = 100.2dB SFDR = 117.4dB –40 –8 200 4000 0 8 128k Point FFT fSMPL = 1.5Msps, fIN = 2kHz –20 8000 0 100 238024 G05 DC Histogram, N = 65536, fSMPL = 2Msps 6000 6 AMPLITUDE (dBFS) 10000 0 CODE 2000 238024 G04 COUNTS 10000 σ = 1.75 8000 –200 –100 238024 G03 8000 0 –300 –200 238024 G02 COUNTS COUNTS 10000 0 –300 8388608 12582912 16777216 OUTPUT CODE –180 0 12.5 25 37.5 FREQUENCY (kHz) 50 62.5 238024 G09 238024f 6 For more information www.linear.com/LTC2380-24 LTC2380-24 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VDD = 2.5V, OVDD = 2.5V, VCM = 2.5V, REF = 5V, fSMPL = 1.5Msps, N = 1, unless otherwise noted. 0 128k Point FFT fSMPL = 2Msps, fIN = 100Hz, N = 1024 –40 –60 –60 –100 –120 –140 AMPLITUDE (dBFS) –40 –60 –80 –80 –100 –120 –140 –120 –140 –160 –180 –180 –180 –200 –200 488 732 FREQUENCY (Hz) 976 0 15.3 30.5 45.8 FREQUENCY (Hz) 110 SNR THD, HARMONICS (dBFS) 1 98 97 SINAD 96 95 94 92 0.1 70k 0 25 50 75 100 125 150 175 200 FREQUENCY (kHz) SNR, SINAD vs Input level, fIN = 2kHz 101 THD 3RD –110 2ND –120 –130 SNR, SINAD (dBFS) SNR 100.5 SINAD 99.5 –115.0 SNR 0 25 50 75 100 125 150 175 200 FREQUENCY (kHz) 99 0 SINAD 98 98 97 238024 G16 95 2.5 THD, Harmonics vs Reference Voltage, fIN = 2kHz –120.0 THD 3RD –125.0 –130.0 2ND –135.0 –140.0 96 –20 –10 INPUT LEVEL (dB) –140 238024 G15 SNR, SINAD vs Reference Voltage, fIN = 2kHz 100 101.0 –30 –100 238024 G14 238024 G13 THD, HARMONICS (dBFS) 10 100 1k 10k NUMBER OF AVERAGES (N) 99.0 –40 15 93 DYNAMIC RANGE 100.0 12 –90 99 SNR, SINAD (dBFS) 120 TRANSITION NOISE (LSB) 130 101.5 6 9 FREQUENCY (Hz) 100 10 1 3 THD, Harmonics vs Input Frequency 101 TRANSITION NOISE 140 100 0 238024 G12 SNR, SINAD vs Input Frequency 100 150 –200 61 238024 G11 Dynamic Range, Transition Noise vs Number of Averages (N) DYNAMIC RANGE (dB) –100 –160 244 DR = 145dB –80 –160 0 8k Point FFT fSMPL = 2Msps, IN+ = IN– = VCM, N = 65536 –20 –40 238024 G10 SNR, SINAD (dBFS) 0 SNR = 138.3dB –20 AMPLITUDE (dBFS) AMPLITUDE (dBFS) 0 SNR = 130.2dB –20 32k Point FFT fSMPL = 2Msps, fIN = 10Hz, N = 16384 3 3.5 4 4.5 REFERENCE VOLTAGE (V) 5 238024 G17 –145.0 2.5 3 3.5 4 4.5 REFERENCE VOLTAGE (V) 5 238024 G18 238024f For more information www.linear.com/LTC2380-24 7 LTC2380-24 TYPICAL PERFORMANCE CHARACTERISTICS REF = 5V, fSMPL = 1.5Msps, N = 1, unless otherwise noted. 99.5 99.0 –15 10 35 TEMPERATURE (°C) 60 2.0 3RD –120 –125 –130 MAX INL 1.0 0 –1.0 –2.0 2ND MIN INL –3.0 –140 –40 85 3.0 THD –135 98.5 –40 INL vs Temperature 4.0 INL ERROR (PPM) SINAD 100.0 THD, Harmonics vs Temperature, fIN = 2kHz –115 SNR 100.5 SNR, SINAD (dBFS) –110 THD, HARMONICS (dBFS) 101.0 SNR, SINAD vs Temperature, fIN = 2kHz TA = 25°C, VDD = 2.5V, OVDD = 2.5V, VCM = 2.5V, –15 10 35 TEMPERATURE (°C) 60 238024 G19 85 –4.0 –40 –15 10 35 TEMPERATURE (°C) 60 238024 G20 Full-Scale Error vs Temperature Zero-Scale Error vs Temperature 10 85 238024 G21 Supply Current vs Temperature 5 12 5 –FS 0 +FS –5 10 3 SUPPLY CURRENT (mA) ZERO–SCALE ERROR (ppm) FULL–SCALE ERROR (ppm) 4 2 1 0 –1 –2 –3 8 IVDD – fSMPL = 2Msps, N = 4 IVDD – fSMPL = 1.5Msps, N = 1 IOVDD – fSMPL = 2Msps, N = 4 IOVDD – fSMPL = 1.5Msps, N = 1 IREF – fSMPL = 2Msps, N = 4 IREF – fSMPL = 1.5Msps, N = 1 6 4 2 –4 –10 –40 –15 10 35 TEMPERATURE (°C) 60 –5 –40 85 –15 10 35 TEMPERATURE (°C) 238024 G22 60 0 –40 85 –15 10 35 TEMPERATURE (°C) 60 238024 G23 Power-Down Current vs Temperature 238024 G24 Reference Current vs Reference Voltage CMRR vs Input Frequency 10 85 100 2.0 REFERENCE CURRENT (mA) 95 8 90 6 CMRR (dB) POWER–DOWN CURRENT (µA) IVDD+IOVDD+IREF 4 85 80 2 0 –40 75 –15 10 35 TEMPERATURE (°C) 60 85 238024 G25 70 0.001 0.01 0.1 1 FREQUENCY (MHz) 10 238024 G26 1.5 fSMPL = 2Msps 1.0 fSMPL = 1.5Msps 0.5 2.5 3 3.5 4 4.5 REFERENCE VOLTAGE (V) 5 238024 G27 238024f 8 For more information www.linear.com/LTC2380-24 LTC2380-24 PIN FUNCTIONS CHAIN (Pin 1): Chain Mode Selector Pin. When low, the LTC2380-24 operates in normal mode and the RDL/SDI input pin functions to enable or disable SDO. When high, the LTC2380-24 operates in chain mode and the RDL/SDI pin functions as SDI, the daisy-chain serial data input. Logic levels are determined by OVDD. VDD (Pin 2): 2.5V Power Supply. The range of VDD is 2.375V to 2.625V. Bypass VDD to GND with a 10µF ceramic capacitor. GND (Pins 3, 6, 10 and 16): Ground. IN+, IN– (Pins 4, 5): Positive and Negative Differential Analog Inputs. REF (Pin 7): Reference Input. The range of REF is 2.5V to 5.1V. This pin is referred to the GND pin and should be decoupled closely to the pin with a 47µF ceramic capacitor (X7R, 1210 size, 10V rating). REF/DGC (Pin 8): When tied to REF, digital gain compression is disabled and the LTC2380-24 defines full-scale according to the ±VREF analog input range. When tied to GND, digital gain compression is enabled and the LTC2380-24 defines full-scale with inputs that swing between 10% and 90% of the ±VREF analog input range. CNV (Pin 9): Convert Input. A rising edge on this input powers up the part and initiates a new conversion. Logic levels are determined by OVDD. BUSY (Pin 11): BUSY Indicator. Goes high at the start of a new conversion and returns low when the conversion has finished. Logic levels are determined by OVDD. RDL/SDI (Pin 12): Bus Enabling Input/Serial Data Input Pin. This pin serves two functions depending on whether the part is operating in normal mode (CHAIN pin low) or chain mode(CHAIN pin high). In normal mode, RDL/SDI is a bus enabling input for the serial data I/O bus. When RDL/SDI is low in normal mode, data is read out of the ADC on the SDO pin. When RDL/SDI is high in normal mode, SDO becomes Hi-Z and SCK is disabled. In chain mode, RDL/SDI acts as a serial data input pin where data from another ADC in the daisy chain is input. Logic levels are determined by OVDD. SCK (Pin 13): Serial Data Clock Input. When SDO is enabled, the conversion result or daisy-chain data from another ADC is shifted out on the rising edges of this clock MSB first. Logic levels are determined by OVDD. SDO (Pin 14): Serial Data Output. The conversion result or daisy-chain data is output on this pin on each rising edge of SCK MSB first. The output data is in 2’s complement format. Logic levels are determined by OVDD. OVDD (Pin 15): I/O Interface Digital Power. The range of OVDD is 1.71V to 5.25V. This supply is nominally set to the same supply as the host interface (1.8V, 2.5V, 3.3V, or 5V). Bypass OVDD to GND with a 0.1µF capacitor. GND (Exposed Pad Pin 17 – DFN Package Only): Ground. Exposed pad must be soldered directly to the ground plane. 238024f For more information www.linear.com/LTC2380-24 9 LTC2380-24 FUNCTIONAL BLOCK DIAGRAM VDD = 2.5V OVDD = 1.8V to 5V REF = 5V IN+ IN– CHAIN + 24-BIT SAMPLING ADC DIGITAL FILTER – SPI PORT SDO RDL/SDI SCK CNV CONTROL LOGIC BUSY REF/DGC GND 238024 BD TIMING DIAGRAM Conversion Timing Using the Serial Interface CHAIN, RDL/SDI = 0 CNV BUSY POWER-DOWN AND ACQUIRE CONVERT SCK SDO D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 C15 C14 C13 C12 C11 C10 C9 C8 C7 C6 C5 C4 C3 C2 C1 C0 238024 TD01 DATA FROM CONVERSION NUMBER OF SAMPLES AVERAGED FOR DATA 238024f 10 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION The LTC2380-24 is a low noise, low power, high speed 24-bit successive approximation register (SAR) ADC with an integrated digital averaging filter. Operating from a 2.5V supply, the LTC2380-24 has a ±VREF fully differential input range with VREF ranging from 2.5V to 5.1V. The LTC238024 consumes only 28mW and achieves ±3.5ppm INL maximum and no missing codes at 24 bits. The LTC2380-24 has an easy to use integrated digital averaging filter that can average 1 to 65536 conversion results real-time, dramatically improving dynamic range from 101dB at 1.5Msps to 145dB at 30.5sps. No separate programming interface or configuration register is required. The high speed SPI-compatible serial interface supports 1.8V, 2.5V, 3.3V and 5V logic while also featuring a daisychain mode. The LTC2380-24 automatically powers down between conversions, reducing power dissipation at lower sampling rates. CONVERTER OPERATION The LTC2380-24 operates in two phases. During the acquisition phase, the charge redistribution capacitor D/A converter (CDAC) is connected to the IN+ and IN– pins to sample the differential analog input voltage. A rising edge on the CNV pin initiates a conversion. During the conversion phase, the 24-bit CDAC is sequenced through a successive approximation algorithm, effectively comparing the sampled input with binary-weighted fractions of the reference voltage (e.g. VREF/2, VREF/4 … VREF/16777216) using the differential comparator. At the end of conversion, the CDAC output approximates the sampled analog input. The ADC control logic then passes the 24-bit digital output code to the digital filter for further processing. OUTPUT CODE (2’S COMPLEMENT) OVERVIEW 011...111 BIPOLAR ZERO 011...110 000...001 000...000 111...111 111...110 100...001 FSR = +FS – –FS 1LSB = FSR/16777216 100...000 –FSR/2 –1 0V 1 FSR/2 – 1LSB LSB LSB INPUT VOLTAGE (V) 238024 F02 Figure 2. LTC2380-24 Transfer Function ANALOG INPUT The analog inputs of the LTC2380-24 are fully differential in order to maximize the signal swing that can be digitized. The analog inputs can be modeled by the equivalent circuit shown in Figure 3. The diodes at the input provide ESD protection. In the acquisition phase, each input sees approximately 45pF (CIN) from the sampling CDAC in series with 40Ω (RON) from the on-resistance of the sampling switch. Any unwanted signal that is common to both inputs will be reduced by the common mode rejection of the ADC. The inputs draw a current spike while charging the CIN capacitors during acquisition. During conversion, the analog inputs draw only a small leakage current. REF RON 40Ω IN+ REF IN– RON 40Ω CIN 45pF CIN 45pF BIAS VOLTAGE 238024 F03 TRANSFER FUNCTION The LTC2380-24 digitizes the full-scale voltage of 2 × REF into 224 levels, resulting in an LSB size of 0.6µV with REF = 5V. The ideal transfer function is shown in Figure 2. The output data is in 2’s complement format. Figure 3. The Equivalent Circuit for the Differential Analog Input of the LTC2380-24 INPUT DRIVE CIRCUITS A low impedance source can directly drive the high impedance inputs of the LTC2380-24 without gain error. A high 238024f For more information www.linear.com/LTC2380-24 11 LTC2380-24 APPLICATIONS INFORMATION impedance source should be buffered to minimize settling time during acquisition and to optimize ADC linearity. For best performance, a buffer amplifier should be used to drive the analog inputs of the LTC2380-24. The amplifier provides low output impedance, which produces fast settling of the analog signal during the acquisition phase. It also provides isolation between the signal source and the ADC input currents. Noise and Distortion 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 an appropriate filter to minimize noise. The simple 1-pole RC lowpass filter (LPF1) shown in Figure 4 is sufficient for many applications. LPF2 SINGLE-ENDEDINPUT SIGNAL LPF1 500Ω 6600pF 6800pF 10Ω IN+ 3300pF 10Ω SINGLE-ENDED- 6800pF BW = 48kHz TO-DIFFERENTIAL DRIVER BW = 1.2MHz LTC2380-24 IN– 238024 F04 Figure 4. Input Signal Chain A coupling filter network (LPF2) should be used between the buffer and ADC input to minimize disturbances reflected into the buffer from sampling transients. Long RC time constants at the analog inputs will slow down the settling of the analog inputs. Therefore, LPF2 typically requires a wider bandwidth than LPF1. This filter also helps minimize the noise contribution from the buffer. A buffer amplifier with a low noise density must be selected to minimize degradation of the SNR. High quality capacitors and resistors should be used in the RC filters since these components can add distortion. NP0 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. Input Currents One of the biggest challenges in coupling an amplifier to the LTC2380-24 is in dealing with current spikes drawn by the ADC inputs at the start of each acquisition phase. The ADC inputs may be modeled as a switched capacitor load of the drive circuit. A drive circuit may rely partially on attenuating switched-capacitor current spikes with small filter capacitors CFILT placed directly at the ADC inputs, and partially on the driver amplifier having sufficient bandwidth to recover from the residual disturbance. Amplifiers optimized for DC performance may not have sufficient bandwidth to fully recover at the ADC’s maximum conversion rate, which can produce nonlinearity and other errors. Coupling filter circuits may be classified in three broad categories: Fully Settled – This case is characterized by filter time constants and an overall settling time that is considerably shorter than the sample period. When acquisition begins, the coupling filter is disturbed. For a typical first order RC filter, the disturbance will look like an initial step with an exponential decay. The amplifier will have its own response to the disturbance, which may include ringing. If the input settles completely (to within the accuracy of the LTC2380-24), the disturbance will not contribute any error. Partially Settled – In this case, the beginning of acquisition causes a disturbance of the coupling filter, which then begins to settle out towards the nominal input voltage. However, acquisition ends (and the conversion begins) before the input settles to its final value. This generally produces a gain error, but as long as the settling is linear, no distortion is produced. The coupling filter’s response is affected by the amplifier’s output impedance and other parameters. A linear settling response to fast switchedcapacitor current spikes can NOT always be assumed for precision, low bandwidth amplifiers. The coupling filter serves to attenuate the current spikes’ high-frequency energy before it reaches the amplifier. Fully Averaged – If the coupling filter capacitors (CFILT) at the ADC inputs are much larger than the ADC’s sample capacitors (45pF), then the sampling glitch is greatly attenuated. The driving amplifier effectively only sees the 238024f 12 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION average sampling current, which is quite small. At 2Msps, the equivalent input resistance is approximately 11k (as shown in Figure 5), a benign resistive load for most precision amplifiers. However, resistive voltage division will occur between the coupling filter’s DC resistance and the ADC’s equivalent (switched-capacitor) input resistance, thus producing a gain error. IN+ REQ LTC2380-24 CFILT >> 45pF BIAS VOLTAGE IN– CFILT >> 45pF REQ 238024 F05 REQ = 1 fSMPL • 45pF Figure 5. Equivalent Circuit for the Differential Analog Input of the LTC2380-24 at 2Msps The input leakage currents of the LTC2380-24 should also be considered when designing the input drive circuit, because source impedances will convert input leakage currents to an added input voltage error. The input leakage currents, both common mode and differential, are typically extremely small over the entire operating temperature range. Figure 6 shows input leakage currents over temperature for a typical part. INPUT LEAKAGE (nA) 10 VIN = VREF DIFFERENTIAL 5 0 COMMON –5 –40 –15 10 35 TEMPERATURE (°C) 60 85 238024 F06 Figure 6. Common Mode and Differential Input Leakage Current over Temperature Let RS1 and RS2 be the source impedances of the differential input drive circuit shown in Figure 7, and let IL1 and IL2 be the leakage currents flowing out of the ADC’s analog inputs. The voltage error, VE, due to the leakage currents can be expressed as: VE = RS1 +RS2 I +I • (IL1 –IL2 ) + (RS1 –RS2 ) • L1 L2 2 2 The common mode input leakage current, (IL1 + IL2)/2, is typically extremely small (Figure 6) over the entire operating temperature range and common mode input voltage range. Thus, any reasonable mismatch (below 5%) of the source impedances RS1 and RS2 will cause only a negligible error. The differential input leakage current, (IL1 – IL2), increases with temperature as shown in Figure 6 and is maximum when VIN = VREF. The differential leakage current is also typically very small, and its nonlinear component is even smaller. Only the nonlinear component will impact the ADC’s linearity. RS1 IL1 + VE – RS2 IN+ LTC2380-24 IN– IL2 238024 F07 Figure 7. Source Impedances of a Driver and Input Leakage Currents of the LTC2380-24 For optimal performance, it is recommended that the source impedances, RS1 and RS2, be between 5Ω and 50Ω and with 1% tolerance. For source impedances in this range, the voltage and temperature coefficients of RS1 and RS2 are usually not critical. The guaranteed AC and DC specifications are tested with 10Ω source impedances, and the specifications will gradually degrade with increased source impedances due to incomplete settling of the inputs. Fully Differential Inputs A low distortion fully differential signal source driven through the LT6203 configured as two unity gain buffers as shown in Figure 8 can be used to get the full data sheet distortion performance of –117dB. 238024f For more information www.linear.com/LTC2380-24 13 LTC2380-24 APPLICATIONS INFORMATION 5V 0V LT6203 3 2 499Ω 5V 1 LT6203 0V 5V 5V 5 0V + – 6 + – 5V 7 3 0V 2 0V 499Ω 6 5 + – 5V – + OUT2 7 0V 5V OUT1 1 238024 F08 0V Figure 8. LT6203 Buffering a Fully Differential Signal Source 249Ω Single-Ended-to-Differential Conversion Figure 9a shows the LT6203 being used to convert a 0V to 5V single-ended input signal. 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 the amplifier. As shown in the FFT of Figure 9b, the LT6203 drives the LTC2380-24 to near full data sheet performance. Digital Gain Compression + – VCM = REF/2 238024 F09a Figure 9a. LT6203 Converting a 0V to 5V Single-Ended Signal to a ±5V Differential Input Signal 0 SNR = 100.2dB THD = –112.5dB SINAD = 100dB SFDR = 116.7dB –20 –40 AMPLITUDE (dBFS) For single-ended input signals, a single-ended-todifferential conversion circuit must be used to produce a differential signal at the inputs of the LTC2380-24. The LT6203 ADC driver is recommended for performing single-ended-to-differential conversions. The LT6203 is flexible and may be configured to convert single-ended signals of various amplitudes to the ±5V differential input range of the LTC2380-24. 10µF –60 –80 –100 –120 –140 –160 –180 0 150 300 450 FREQUENCY (kHz) 600 750 238024 F09b The LTC2380-24 offers a digital gain compression (DGC) feature which defines the full-scale input swing to be be tween 10% and 90% of the ±VREF analog input range. To enable digital gain compression, bring the REF/DGC pin low. This feature allows the SAR ADC driver to be powered off of a single positive supply since each input swings between 0.5V and 4.5V as shown in Figure 10. Needing only one positive supply to power the SAR ADC driver results in additional power savings for the entire system. With DGC enabled, the LTC2380-24 can be driven by the low power LTC6362 differential driver which is powered from a single 5V supply. Figure 11a shows how to configure the LTC6362 to accept a ±3.28V true bipolar single-ended input signal and level shift the signal to the reduced input range of the LTC2380-24 when digital gain compression is enabled. When paired with the LTC6655-4.096 for the Figure 9b. 128k Point FFT Plot with fIN = 2kHz for Circuit Shown in Figure 9a 5V 4.5V 0.5V 0V 238024 F10 Figure 10. Input Swing of the LTC2380-24 with Gain Compression Enabled reference, the entire signal chain solution can be powered from a single 5V supply, minimizing power consumption and reducing complexity. As shown in the FFT of Figure 11b, the single 5V supply solution can achieve up to 96dB of SNR. 238024f 14 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION VIN LTC6655-4.096 5V 0 VOUT_F 4.096V –40 1k VCM 10µF 1k V+ 1k 3.28V 0V –3.28V 8 4 + LTC6362 1k VCM 3 1 5 V– 1k 2.5V 6800pF 0.41V IN+ 35.7Ω 6 IN– 35.7Ω 3.69V REF VDD LTC2380-24 3300pF – 2 3.69V 6800pF REF/DGC 238024 F11a 0.41V AMPLITUDE (dBFS) 1k 47µF SNR = 98.2dB THD = –107.7dB SINAD = 97.7dB SFDR = 111dB –20 VOUT_S –60 –80 –100 –120 –140 –160 –180 0 150 300 450 FREQUENCY (kHz) 600 750 238024 F11b Figure 11a. LTC6362 Configured to Accept a ±3.28V Input Signal While Running from a Single 5V Supply When Digital Gain Compression Is Enabled in the LTC2380-24 DC Accuracy Many driver circuits presented in this data sheet emphasize AC performance (Distortion and Signal to Noise Ratio), and the amplifiers are chosen accordingly. The very low level of distortion is a direct consequence of the excellent INL of the LTC2380-24, and this property can be exploited in DC applications as well. Note that while the LTC6362 and LT6203 are characterized by excellent AC specifications, their DC specifications do not match those of the LTC2380-24. The offset of these amplifiers, for example, is more than 500μV under certain conditions. In contrast, the LTC2380-24 has a guaranteed maximum offset error of 130µV (typical drift ±0.007ppm/°C), and a guaranteed maximum full-scale error of 100ppm (typical drift ±0.05ppm/°C). Low drift is important to maintain accuracy over wide temperature ranges in a calibrated system. Amplifiers have to be selected very carefully to provide a 24-bit accurate DC signal chain. A large-signal open-loop gain of at least 126dB may be required to ensure 1ppm linearity for amplifiers configured for a gain of negative 1. However, less gain is sufficient if the amplifier’s gain characteristic is known to be (mostly) linear. An amplifier’s offset versus signal level must be considered for amplifiers configured as unity gain buffers. For example, 1ppm linearity may require that the offset is known to vary less than 5μV for a 5V swing. However, greater offset variations may be acceptable if the relationship is known to be (mostly) linear. Unity-gain buffer amplifiers typically Figure 11b. 128k Point FFT Plot with fIN = 2kHz for Circuit Shown in Figure 11a require substantial headroom to the power supply rails for best performance. Inverting amplifier circuits configured to minimize swing at the amplifier input terminals may perform better with less headroom than unity-gain buffer amplifiers. The linearity and thermal properties of an inverting amplifier’s feedback network should be considered carefully to ensure DC accuracy. ADC REFERENCE The LTC2380-24 requires an external reference to define its input range. A low noise, low temperature drift reference is critical to achieving the full data sheet performance of the ADC. Linear Technology offers a portfolio of high performance references designed to meet the needs of many applications. With its small size, low power and high accuracy, the LTC6655-5 is particularly well suited for use with the LTC2380-24. The LTC6655-5 offers 0.025% (max) initial accuracy and 2ppm/°C (max) temperature coefficient for high precision applications. When choosing a bypass capacitor for the LTC6655-5, the capacitor’s voltage rating, temperature rating, and package size should be carefully considered. Physically larger capacitors with higher voltage and temperature ratings tend to provide a larger effective capacitance, better filtering the noise of the LTC6655-5, and consequently producing a higher SNR. Therefore, we recommend bypassing the LTC6655-5 with a 47μF ceramic capacitor (X7R, 1210 size, 10V rating) close to the REF pin. 238024f For more information www.linear.com/LTC2380-24 15 LTC2380-24 APPLICATIONS INFORMATION The REF pin of the LTC2380-24 draws charge (QCONV) from the 47µF bypass capacitor during each conversion cycle. The reference replenishes this charge with a DC current, IREF = QCONV/tCYC. The DC current draw of the REF pin, IREF, depends on the sampling rate and output code. If the LTC2380-24 is used to continuously sample a signal at a constant rate, the LTC6655-5 will keep the deviation of the reference voltage over the entire code span to less than 0.5ppm. improvement of the SNR as N increases, because any noise on the REF pin will modulate around the fundamental frequency of the input signal. Therefore, it is critical to use a low-noise reference, especially if the input signal amplitude approaches full-scale. For small input signals, the dynamic range will improve as described earlier in this section. When idling, the REF pin on the LTC2380-24 draws only a small leakage current (< 1µA). In applications where a burst of samples is taken after idling for long periods as shown in Figure 12, IREF quickly goes from approximately 0µA to a maximum of 2mA at 2Msps. This step in DC current draw triggers a transient response in the reference that must be considered since any deviation in the reference output voltage will affect the accuracy of the output code. In applications where the transient response of the reference is important, the fast settling LTC6655-5 reference is also recommended. 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 LTC2380-24 provides guaranteed tested limits for both AC distortion and noise measurements. In applications where power management is critical, the external reference may be powered down such that the voltage on the REF pin can go below 2V. In such scenarios, it is recommended that after the voltage on the REF pin recovers to above 2V, the ADC’s internal digital I/O registers be cleared before the initiation of the next conversion. This can be achieved by providing at least 20 rising edges on the SCK pin before the first CNV rising edge. Reference Noise The dynamic range of the ADC will increase approximately 3dB for every 2× increase in the number of conversion results averaged (N). The SNR should also improve as a function of N in the same manner. For large input signals near full-scale, however, any reference noise will limit the DYNAMIC PERFORMANCE Dynamic Range The dynamic range is the ratio of the RMS value of a full scale input to the total RMS noise measured with the inputs shorted to VREF/2. The dynamic range of the LTC2380-24 without averaging (N = 1) is 101dB which improves by 3dB for every 2× increase in the number of conversion results averaged (N) per measurement. Signal-to-Noise and Distortion Ratio (SINAD) 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 ADC output. The output is band-limited to frequencies from above DC and below half the sampling frequency. Figure 13 shows that the LTC2380-24 achieves a typical SINAD of 100dB at a 1.5MHz sampling rate with a 2kHz input. CNV IDLE PERIOD IDLE PERIOD 238024 F12 Figure 12. CNV Waveform Showing Burst Sampling 238024f 16 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION 0 SNR = 100.3dB THD = –117.3dB SINAD = 100.2dB SFDR = 117.4dB –20 AMPLITUDE (dBFS) –40 –60 –80 Power Supply Sequencing –100 –120 –140 –160 –180 0 150 300 450 FREQUENCY (kHz) 600 750 238024 F13 Figure 13. 128k Point FFT Plot of the LTC2380-24 with fIN = 2kHz and fSMPL = 1.5MHz Signal-to-Noise Ratio (SNR) 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 13 shows that the LTC2380-24 achieves a typical SNR of 100dB at a 1.5MHz sampling rate with a 2kHz input. 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: interface power supply (OVDD). The flexible OVDD supply allows the LTC2380-24 to communicate with any digital logic operating between 1.8V and 5V, including 2.5V and 3.3V systems. 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 LTC2380-24 provides two power supply pins: the 2.5V power supply (VDD), and the digital input/output The LTC2380-24 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 LTC238024 has a power-on-reset (POR) circuit that will reset the LTC2380-24 at initial power-up or whenever the power supply voltage drops below 1V. Once the supply voltage re-enters the nominal supply voltage range, the POR will reinitialize the ADC. No conversions should be initiated until 200µs after a POR event to ensure the re-initialization period has ended. Any conversions initiated before this time will produce invalid results. In addition, after a POR event, it is recommended that the ADC’s internal digital I/O registers be cleared before the initiation of the next conversion. This can be achieved by providing at least 20 rising edges on the SCK pin before the first CNV rising edge. TIMING AND CONTROL CNV Timing The LTC2380-24 conversion is controlled by CNV. A rising edge on CNV will start a conversion and power up the LTC2380-24. Once a conversion has been initiated, it cannot be restarted until the conversion is complete. For optimum performance, CNV should be driven by a clean low jitter signal. Converter status is indicated by the BUSY output which remains high while the conversion is in progress. To ensure that no errors occur in the digitized results, any additional transitions on CNV should occur within 40ns from the start of the conversion or after the conversion has been completed. Once the conversion has completed, the LTC2380-24 powers down and begins acquiring the input signal. 238024f For more information www.linear.com/LTC2380-24 17 LTC2380-24 APPLICATIONS INFORMATION Internal Conversion Clock DIGITAL INTERFACE The LTC2380-24 has an internal clock that is trimmed to achieve a maximum conversion time of 372ns. With a minimum acquisition time of 115ns, a maximum sample rate of 2Msps is guaranteed without any external adjustments. Note that the serial I/O data transfer time limits the output data rate (fODR) to 1.5Msps (See Conventional SAR Operation section). A sample rate of 2Msps is achievable when averaging 4 or more conversion results while using a distributed read (See Distributed Read section). The LTC2380-24 features a simple and easy to use serial digital interface that supports output data rates up to 1.5Msps. The interface controls a digital averaging filter, which can be used to increase the dynamic range of measurements. The flexible OVDD supply allows the LTC2380-24 to communicate with any digital logic operating between 1.8V and 5V, including 2.5V and 3.3V systems. The digital interface of the LTC2380-24 is backwards compatible with the LTC2378-20 family. Auto Power-Down Digital Averaging Filter (SINC1 Decimation Filter) The LTC2380-24 automatically powers down after a conversion has been completed and powers up once a new conversion is initiated on the rising edge of CNV. During power-down, data from the last conversion can be clocked out. To minimize power dissipation during power-down, disable SDO and turn off SCK. The auto power-down feature will reduce the power dissipation of the LTC2380-24 as the sampling rate is reduced. Since power is consumed only during a conversion, the LTC2380-24 remains powereddown for a larger fraction of the conversion cycle (tCYC) at lower sample rates, thereby reducing the average power dissipation which scales with the sampling rate as shown in Figure 14. Many SAR ADC applications use digital averaging techniques to reduce the uncertainty of measurements due to noise. An FPGA or DSP is typically needed to compute the average of multiple A/D conversion results. The LTC2380-24 features an integrated digital averaging filter that can provide the function without any additional hardware, thus simplifying the application solution and providing a number of unique advantages. The digital averaging filter can be used to average blocks of as few as N = 1 or as many as N = 65536 conversion results. 12 SUPPLY CURRENT (mA) Block Diagram label2IVDD, N = 4 label6 label5 label4 label3 IOVDD, N = 4 IREF IVDD, N = 1 IOVDD, N = 1 10 8 The digital averaging filter described in this section is also known as a SINC1 digital decimation filter. A SINC1 digital decimation filter is an FIR filter with N equal-valued taps. Figure 15 illustrates a block diagram of the digital averaging filter, including a Conversion Result Register, the Digital Signal Processing (DSP) block, and an I/O Register. The Conversion Result Register holds the 24-bit conversion result from the most recent sample taken at the rising edge 6 4 2 0 DIGITAL AVERAGING FILTER 0 0.5 1 1.5 SAMPLING RATE (Msps) 2 24-BIT SAMPLING ADC 238024 F14 Figure 14. Power Supply Current of the LTC2380-24 Versus Sampling Rate CNV CONVERSION RESULT REGISTER DIGITAL SIGNAL PROCESSING I/O REGISTER SDO SCK 238024 F15 Figure 15. Block Diagram with Digital Averaging Filter 238024f 18 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION Reducing Measurement Noise Using the Digital Averaging Filter of CNV. The DSP block provides an averaging operation, loading average values of conversion results into the I/O Register for the user to read through the serial interface. Digital averaging techniques are often employed to reduce the uncertainty of measurements due to noise. The LTC2380-24 features a digital averaging filter, making it easy to perform an averaging operation without providing any additional hardware and software. Conventional SAR Operation The LTC2380-24 may be operated like a conventional nolatency SAR as shown in Figure 16. Each conversion result is read out via the serial interface before the next conversion is initiated. Note how the contents of the I/O Register track the contents of the Conversion Result Register and that both registers contain a result corresponding to a single conversion. The digital averaging filter is transparent to the user when the LTC2380-24 is operated in this way. No programming is required. Simply read out each conversion result in each cycle. Ri represents the 24-bit conversion result corresponding to conversion number i. As few as 20 SCKs may be given in each conversion cycle (instead of the 24 shown in Figure 16) to obtain a 20-bit accurate result, making the LTC2380-24 backwards compatible with the LTC2378-20. A maximum sampling rate of 1.5Msps can be used when operating the LTC2380-24 like a conventional SAR. CONVERSION 0 NUMBER 1 2 3 Averaging 4 Conversion Results Figure 17 shows a case where an output result is read out once for every 4 conversions initiated. As shown, the output result read out from the I/O Register is the average of the 4 previous conversion results. The digital averaging filter will automatically average conversion results until an output result is read out. When an output result is read out, the digital averaging filter is reset and a new averaging operation starts with the next conversion result. In this example, output results are read out after conversion numbers 0, 4 and 8. The digital averaging filter is reset after 4 5 6 7 8 CNV BUSY CONVERSION RESULT REGISTER R0 R1 R2 R3 R4 R5 R6 R7 R8 I/O REGISTER R0 R1 R2 R3 R4 R5 R6 R7 R8 1 24 1 24 1 24 1 24 1 24 1 24 1 24 1 24 1 24 SCK 238024 F16 Figure 16. Conventional SAR Operation Timing 238024f For more information www.linear.com/LTC2380-24 19 LTC2380-24 APPLICATIONS INFORMATION CONVERSION 0 NUMBER 2 1 3 4 5 6 7 8 CNV BUSY CONVERSION RESULT REGISTER I/O REGISTER R0 R1 R2 R3 R4 R5 R6 R7 R8 R(–3)+R(–2)+R(–1)+R0 4 R1 R1 + R2 2 R1 + R2 + R3 4 R1 + R2 + R3 + R4 4 R5 R5 + R6 2 R5 + R6 + R7 4 R5 + R6 + R7 + R8 4 1 24 1 24 1 24 SCK 238024 F17 Figure 17. Averaging 4 Conversion Results conversion number 0 and starts a new averaging operation beginning with conversion number 1. The output result (R1 + R2 + R3 + R4)/4 is read out after conversion number 4, which resets the digital averaging filter again. Since the digital averaging filter automatically averages conversion results for each new conversion performed, an arbitrary number of conversion results, up to the upper limit of 65536, may be averaged with no programming required. Averaging 3 Conversion Results The output result, when averaging N conversion results for values of N that are not a power of 2, will be scaled by N/M, where M is a weighting factor that is the next power of 2 greater than N (described later in the Weighting Factor section). Figure 18 shows an example where only 3 conversion results are averaged. The output result read out is scaled by N/M = ¾. Using the Digital Averaging Filter with Reduced Data Rate The examples given in Figures 16, 17 and 18 illustrate some of the most common ways to use the LTC2380-24. Simply read each individual conversion result, or read an average of N conversion results. In each case, the result is read out between two consecutive A/D conversion (BUSY) periods, limiting the sampling rate to 1.5Msps with a 100MHz clock (see Timing Diagrams). Distributed Read Sampling rates greater than 1.5Msps are achievable when using a distributed read. Distributed reads require that multiple conversion results be averaged. A minimum of 4 conversion results must be averaged to run the LTC238024 at its maximum sampling rate of 2Msps. If at least 1 but less than 20 SCK pulses(0 < SCKs < 20) are given in a conversion cycle between 2 BUSY falling edges (See Figure 19), the I/O Register is not updated with the output of the digital averaging filter, preserving its contents. This allows an output result to be read from the I/O Register over multiple conversion cycles, easing the speed requirements of the serial interface. A read is initiated by a rising edge of a first SCK pulse and it must be terminated before a next read can be initiated. The digital averaging filter is reset upon the initiation of a read wherein a new averaging operation begins. Conver- 238024f 20 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION CONVERSION 0 NUMBER 1 2 3 4 5 6 7 8 CNV BUSY CONVERSION RESULT REGISTER I/O REGISTER R0 R1 R2 R3 R4 R5 R6 R7 R8 R(–2) + R(–1) + R0 4 R1 R1 + R2 2 R1 + R2 + R3 4 R4 R4 + R5 2 R4 + R5 + R6 4 R7 R7 + R8 2 1 24 1 24 1 24 SCK 238024 F18 Figure 18. Averaging 3 Conversion Results sions completed after the digital averaging filter is reset will automatically be averaged until a new read is initiated. Thus, the digital averaging filter will calculate averages of conversion results from conversions completed between a time when one read is initiated to when a next read is initiated. A read is terminated by providing either 0 or greater than 19 SCK pulses (rising edges) in a conversion cycle between 2 BUSY falling edges, allowing the I/O Register to be updated with new averages from the output of the digital averaging filter. Averaging 4 Conversions Using a Distributed Read Figure 19 shows an example where reads are initiated every 4 conversion cycles, and the I/O register is read over 3 conversion cycles. This allows the serial interface to run at 1/3 of the speed that it would otherwise have to run. The first rising SCK edge initiates a 1st read, and 3 groups of 8-bits are read out over 3 conversion cycles. No SCK pulses are provided between the BUSY falling edges of conversion numbers 4 and 5, whereby the read is terminated at the completion of conversion number 5. A second read is initiated after conversion number 5, which results in (R2 + R3 + R4 + R5)/4 being read out from the I/O Register since conversion numbers 2, 3, 4 and 5 completed between the initiation of the two reads shown. Averaging 25 Conversions Using a Distributed Read Figure 20 shows an example where a read is initiated every 25 conversion cycles, using a single SCK pulse per conversion cycle to read the output result from the I/O Register. The first rising SCK edge initiates a read where a single bit is then read out over the next 23 conversion cycles. No SCK pulses are provided between the BUSY falling edges of conversion numbers 25 and 26, whereby the read is terminated at the completion of conversion number 26. A 2nd read is initiated after conversion number 26, resulting in (R2 + R3 +…+ R25 + R26)/32 being read out from the I/O Register. Since 0 < SCKs < 20 pulses are given each conversion period during the read, the contents of the I/O Register are not updated, allowing the distributed read to occur without interruption. 238024f For more information www.linear.com/LTC2380-24 21 LTC2380-24 APPLICATIONS INFORMATION CONVERSION 0 NUMBER 1 2 3 4 5 6 7 8 CNV CONVERSIONS COMPLETED BETWEEN INITIATION OF READS BUSY CONVERSION RESULT REGISTER R1 R0 R2 R3 R4 R5 R6 R8 R7 BLOCK OF CONVERSION RESULTS AVERAGED FOR 1 MEASUREMENT I/O R(–6) +R(–5) +R(–4) +R(–3) REGISTER 4 R(–2) + R(–1) + R0 + R1 4 1 8 9 16 17 R2 + R3 + R4 + R5 4 24 1 8 9 16 17 24 SCK 0 SCKs 0 < SCKs < 20 0 < SCKs < 20 0 < SCKs < 20 0 SCKs 0 < SCKs < 20 0 < SCKs < 20 1ST READ 0 < SCKs < 20 0 SCKs 2ND READ READ READ TERMINATED INITIATED DIGITAL AVERAGING FILTER RESETS 238024 F19 READ READ TERMINATED INITIATED DIGITAL AVERAGING FILTER RESETS Figure 19. Averaging 4 Conversion Results and Reading Out Data with a Distributed Read CONVERSION 0 NUMBER 1 2 3 4 23 24 25 26 27 CNV CONVERSIONS COMPLETED BETWEEN INITIATION OF READS BUSY CONVERSION RESULT REGISTER R1 R0 R2 I/O REGISTER R3 R23 R24 R25 R(–23) + R(–22) +…+ R0 + R1 (REPEATING READ PATTERN – AVERAGE OF 25 CONVERSION 32 RESULTS FROM 25 CONVERSIONS PRECEDING INITIATION OF READ) 1 2 3 4 23 24 R26 R2 + R3 +…+ R25 + R26 32 1 SCK 0 SCKs 0 < SCKs < 20 0 < SCKs < 20 0 < SCKs < 20 1 SCK/CNV 0 < SCKs < 20 0 < SCKs < 20 0 SCKs READ 0 < SCKs < 20 238024 F20 Figure 20. Averaging 25 Conversion Results and Reading Out Data with a Distributed Read 238024f 22 For more information www.linear.com/LTC2380-24 LTC2380-24 APPLICATIONS INFORMATION Minimum Shift Clock Frequency Table 1. Weighting Factors and Throughput for Various Values of N Requiring at least 1 SCK pulse per conversion cycle while performing a read sets a lower limit on the SCK frequency that can be used which is: fSCK = fSMPL. N M 1 1 1.5Msps 2 2 750ksps Noise vs Averaging 3 4 fSMPL = 1.5Msps 4 Weighting Factor When conversion results are averaged, the resulting output code represents an equally weighted average of the previous N samples if N is a power of 2. If N is not a power of 2, a weighting factor, M, is chosen according to Table 1. Specifically, if Ri represents the 24-bit conversion result of the ith analog sample, then the output code, D, representing N averaged conversion results is defined as: N Ri i=1 M Table 1 illustrates weighting factors for any number of averages, N, between 1 and 65536 and the resulting data throughputs. Note that M reaches a maximum value of 65536 when N = 65536. For N > 65536, the digital averaging filter will continue to accumulate conversion results such that N/M > 1. In such a case, if the ADC core produces conversion results that have a non-zero mean, the output result will eventually saturate at positive or negative full-scale. 500ksps fSMPL = 2Msps The noise of the ADC is un-correlated from one sample to the next. As a result, the ADC noise for a measurement will decrease by √N where N is the number of A/D conversion results averaged for a given measurement. Other noise sources, such as noise from the input buffer amplifier and reference noise may be correlated from sample-to-sample and may be reduced by averaging, but to a lesser extent. D= ∑ OUTPUT DATA RATE 4 500ksps 5-8 8 400ksps - 250ksps 9 - 16 16 222.2ksps - 125ksps 17 - 32 32 117.6ksps - 62.5ksps 33 - 64 64 60.6ksps - 31.3ksps 65 - 128 128 30.8ksps - 15.6ksps 129 - 256 256 15.5ksps - 7.8ksps 257 - 512 512 7.8ksps - 3.9ksps 513 - 1024 1024 3.9ksps - 2ksps 1025 - 2048 2048 2ksps - 1ksps 2049 - 4096 4096 976sps - 488sps 4097 - 8192 8192 488sps - 244sps 8193 - 16384 16384 244sps - 122sps 16385 - 32768 32768 122sps - 61sps 32769 - 65536 65536 61sps - 30.5sps In cases where N/M < 1, achieving a full-scale output result would require driving the analog inputs beyond the specified guaranteed input differential voltage range. Doing so is strongly discouraged since operation of the LTC2380-24 beyond guaranteed specifications could result in undesired behavior, possibly corrupting results. For proper operation, it is recommended that the analog input differential voltage not exceed the ±VREF specification. Note that the output results do not saturate at N/M when N/M < 1. 50Hz and 60Hz Rejection Particular input frequencies may be rejected by selecting the appropriate number of averages, N, based on the sampling rate, fSMPL, and the desired frequency to be rejected, fREJECT. If, TAVG = 1 fSMPL •N= 1 fREJECT 238024f For more information www.linear.com/LTC2380-24 23 LTC2380-24 APPLICATIONS INFORMATION then, D is an average value for a full sine wave cycle of fREJECT, resulting in zero gain for that particular frequency and integer multiples thereof up to fSMPL – fREJECT (See Figure 21). Solving for N gives: fSMPL –40 fREJECT Using this expression, we can find N for rejecting 50Hz and 60Hz as well as other frequencies. Note that N and fSMPL may be traded off to achieve rejection of particular frequencies as shown below. To reject 50Hz with fSMPL = 2Msps: 2,000,000sps 50Hz = 40,000 To reject both 50Hz and 60Hz (each being a multiple of 10Hz), with N = 1024: fSMPL= 1024 • 10Hz –60 0 250 500 750 1000 1250 1500 1750 2000 FREQUENCY (kHz) 238024 F21 Figure 21. SINC1 Filter with fSMPL = 2Msps and N = 8 Count N= –20 GAIN (dB) N= 0 = 10.24ksps Figure 21 shows an example of a SINC1 filter where fSMPL = 2Msps and N = 8, resulting in fREJECT = 250kHz. Note that input frequencies above DC other than fREJECT or multiples thereof are also attenuated to varying degrees due to the averaging operation. In addition to the 24-bit output code, a 16-bit WORD, C[15:0], is appended to produce a total output WORD of 40 bits, as shown in Figure 22. C[15:0] is the straight binary representation (MSB first) of the number of samples averaged to produce the output result minus one. For instance, if N samples are averaged to produce the output result, C[15:0] will equal N – 1. Thus, if N is 1 which is the case with no averaging, C[15:0] will always be 0. If N is 16384, then C[15:0] will equal 16383, and so on. If more than 65536 samples are averaged, then C[15:0] saturates at 65535. CHAIN, RDL/SDI = 0 CNV BUSY POWER-DOWN AND ACQUIRE CONVERT SCK SDO D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 C15 C14 C13 C12 C11 C10 C9 C8 C7 C6 C5 C4 C3 C2 C1 C0 238024 F22 DATA FROM CONVERSION NUMBER OF SAMPLES AVERAGED FOR DATA Figure 22. Serial Output Code Parsing 238024f 24 For more information www.linear.com/LTC2380-24 LTC2380-24 TIMING DIAGRAMS Normal Mode, Single Device SDO is driven. Figure 23 shows a single LTC2380-24 operated in normal mode with CHAIN and RDL/SDI tied to ground. With RDL/SDI grounded, SDO is enabled and the MSB(D23) of the output result is available tDSDOBUSYL after the falling edge of BUSY. The count information is shifted out after the output result. When CHAIN = 0, the LTC2380-24 operates in normal mode. In normal mode, RDL/SDI enables or disables the serial data output pin SDO. If RDL/SDI is high, SDO is in high impedance and SCK is ignored. If RDL/SDI is low, CONVERT CHAIN DIGITAL HOST CNV BUSY IRQ LTC2380-24 RDL/SDI SDO SCK DATA IN CLK 238024 F23a POWER-DOWN AND ACQUIRE CONVERT CHAIN = 0 RDL/SDI = 0 POWER-DOWN AND ACQUIRE CONVERT tCYC tCNVH tCNVL CNV tACQ = tCYC – tCONV – tBUSYLH tCONV BUSY tACQ tBUSYLH tSCK 1 SCK 2 3 SDO C15 22 23 24 tSCKL tHSDO tDSDOBUSYL tQUIET tSCKH tDSDO D23 D22 D21 D1 D0 C15 238024 F23b Figure 23. Using a Single LTC2380-24 in Normal Mode 238024f For more information www.linear.com/LTC2380-24 25 LTC2380-24 TIMING DIAGRAMS Normal Mode, Multiple Devices Since SDO is shared, the RDL/SDI input of each ADC must be used to allow only one LTC2380-24 to drive SDO at a time in order to avoid bus conflicts. As shown in Figure 24, the RDL/SDI inputs idle high and are individually brought low to read data out of each device between conversions. When RDL/SDI is brought low, the MSB of the selected device is output onto SDO. The count information is shifted out after the output result. Figure 24 shows multiple LTC2380-24 devices operating in normal mode (CHAIN = 0) sharing CNV, SCK and SDO. By sharing CNV, SCK and SDO, the number of required signals to operate multiple ADCs in parallel is reduced. RDLB RDLA CONVERT CNV CHAIN RDL/SDI LTC2380-24 B SDO RDL/SDI SCK DIGITAL HOST CNV CHAIN BUSY LTC2380-24 A IRQ SDO SCK DATA IN CLK 238024 F24a POWER-DOWN AND ACQUIRE CONVERT POWER-DOWN AND ACQUIRE CONVERT CHAIN = 0 tCNVL CNV BUSY tCONV tBUSYLH RDL/SDIA RDL/SDIB tSCK 1 SCK tSCKH 2 3 tHSDO tEN SDO Hi-Z tQUIET 22 23 D22A D21A 25 26 27 46 47 48 tSCKL tDIS tDSDO D23A 24 D1A D0A Hi-Z D23B D22B D21B D1B D0B Hi-Z 238024 F24b Figure 24. Normal Mode with Multiple Devices Sharing CNV, SCK and SDO 238024f 26 For more information www.linear.com/LTC2380-24 LTC2380-24 TIMING DIAGRAMS Chain Mode, Multiple Devices number of converters. Figure 25 shows an example with two daisy-chained devices. The MSB of converter A will appear at SDO of converter B after 40 SCK cycles. The MSB of converter A is clocked in at the RDL/SDI pin of converter B on the rising edge of the first SCK pulse. The functionality of the digital averaging filter is preserved when in chain mode. When CHAIN = OVDD, the LTC2380-24 operates in chain mode. In chain mode, SDO is always enabled and RDL/ SDI serves as the serial data pin (SDI) where daisy-chain data output from another ADC can be input. This is useful for applications where hardware constraints may limit the number of lines needed to interface to a large OVDD CONVERT OVDD CHAIN RDL/SDI CNV CHAIN LTC2380-24 A SDO SCK RDL/SDI DIGITAL HOST CNV LTC2380-24 B BUSY IRQ SDO SCK DATA IN CLK 238024 F25a POWER-DOWN AND ACQUIRE CONVERT POWER-DOWN AND ACQUIRE CONVERT CHAIN = OVDD RDL/SDIA = 0 tCNVL CNV BUSY tCONV tBUSYLH tSCKCH 1 SCK 2 3 38 39 tSSDISCK 40 41 tQUIET 42 43 78 79 80 tSCKL tHSDO tHSDISCK SDOA = RDL/SDIB tSCKH tDSDO D23A D22A D21A C1A C0A D23B D22B D21B C1B C0B tDSDOBUSYL SDOB D23A D22A D21A C1A C0A 238024 F25b Figure 25. Chain Mode Timing Diagram 238024f For more information www.linear.com/LTC2380-24 27 LTC2380-24 BOARD LAYOUT To obtain the best performance from the LTC2380-24 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 alongside analog signals or underneath the ADC. Recommended Layout 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 DC2289, the evaluation kit for the LTC2380-24. Top Silkscreen 238024f 28 For more information www.linear.com/LTC2380-24 LTC2380-24 BOARD LAYOUT Layer 1 Component Side Layer 2 Ground Plane 238024f For more information www.linear.com/LTC2380-24 29 LTC2380-24 BOARD LAYOUT Layer 3 PWR Plane Layer 4 Bottom Layer 238024f 30 For more information www.linear.com/LTC2380-24 For more information www.linear.com/LTC2380-24 AIN- 0 - VREF C57 4.7uF 6.3V R49 499 0 - VREF AIN+ CLK IN 100MHz MAX 3.3VPP 0 OHM R55 4 - AC 3 1 C49 OPT AC 1 10uF 6.3V DC C48 1 10uF 6.3V JP8 COUPLING 3 5 3 DC C18 U5 LT6202CS5 C61 V- 0.1uF 25V V- V+ V+ R6 1K 2 JP7 COUPLING C43 OPT C5 0.1uF R5 49.9 1206 3 + C45 0.1uF 25V VREF J2 BNC R57 499 R53 0 OHM J4 BNC J1 BNC 5 2 4 R56 OPT R58 1 OHM R54 OPT C8 1.0uF C44 15pF COG NC7SZ04P5X U8 E5 EXT EXT_CM 4 C2 0.1uF R3 C59 10uF 6.3V C63 1.0uF 25V 2 JP4 CM C60 10uF 6.3V OPT R35 33 OHM U2 NC7SVU04P5X R18 249 VREF/2 2 +3.3V 5 3 C1 0.1uF R36 OPT C66 OPT CLK V- C19 0.1uF 25V C17 1.0uF 25V C420.1uF 25V C40 1.0uF 25V C581.0uF 25V V+ BYPASS CAPS FOR U10 R52 0 OHM C47 0.1uF 25V C68 OPT C62 OPT R44 0 OHM 2 3 - + 1 GND GND GND C39 OPT TP4 TP6 TP7 7 0.1uF R51 10 OHMS C64 6800pF 1206 NPO 4 3 2 1 0402 0 OHM R4 R30 OPT U15 OUTS GND GND GND C9 10uF 6.3V +2.5V C6 10uF 6.3V 5 4 IN- IN+ VREF 5 6 7 8 * C10 0.1uF C7 0.1uF OUTF VIN +3.3V GND SHDN LTC6655AHMS8-5 U1 LTC237XCMS-20 R9 0 OHM 0402 +9V/+10V C11 C55 6800pF 1206 NPO R48 10 OHMS C41 3300pF 1206 NPO U10B LT6203MS8 C65OPT R500 OHM 6 5 VR46 0 OHM - + U10A LT6203MS8 V+ 8 4 +3.3V 2 VDD E3 R7 1K RDL/SDI BUSY SDO SCK CNV C20 47uF 10V 1210 X7R C56 0.1uF VREF 12 11 14 13 9 C12 0.1uF R37 0 OHM C46 2.2uF 10V 2 +3.3V R1 33 OHM 1 RDL TP5 BUSY SDO SCK CNV 2 B 5 3 A OE GND VCC 4 4 1 4 U4 NC7SVU04P5X 33 OHM R15 C3 0.1uF C13 +3.3V 0.1uF 7 8 +3.3V U6 NC7SZ66P5X 5 3 0.8VREF Q Q PR VCC 2 D 1 CP R8 33 OHM CLR GND VREF JP6 FS 6 4 U3 NL17SZ74 R41 33 3 2 2 2K R17 R13 1K U9 NC7SZ04P5X CNVST_33 J3-2 0.1uF C16 QuikEval_DETECT 0.1uF C15 C4 0.1uF +3.3V +3.3V 5 3 R2 1K 15 OVDD 2 2 1 3 7 8 REF REF/DGCL CHAIN 1 GND GND GND GND 3 6 16 10 5 3 +3.3V LTC2380-24 BOARD LAYOUT Partial Schematic of Demo Board 238024f 31 LTC2380-24 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LTC2380-24#packaging for the most recent package drawings. DE Package 16-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1732 Rev Ø) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.45 BSC 3.15 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 9 R = 0.115 TYP 0.40 ±0.10 16 3.30 ±0.10 3.00 ±0.10 (2 SIDES) 1.70 ±0.10 PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) (DE16) DFN 0806 REV Ø 8 0.200 REF 1 0.23 ±0.05 0.45 BSC 0.75 ±0.05 3.15 REF 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC PACKAGE OUTLINE MO-229 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 238024f 32 For more information www.linear.com/LTC2380-24 LTC2380-24 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LTC2380-24#packaging for the most recent package drawings. MS Package 16-Lead Plastic MSOP (Reference LTC DWG # 05-08-1669 Rev A) 0.889 ±0.127 (.035 ±.005) 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 4.039 ±0.102 (.159 ±.004) (NOTE 3) 0.50 (.0197) BSC 0.305 ±0.038 (.0120 ±.0015) TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) DETAIL “A” 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) 0° – 6° TYP 0.280 ±0.076 (.011 ±.003) REF 16151413121110 9 GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 0.18 (.007) SEATING PLANE 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 1234567 8 0.50 (.0197) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.86 (.034) REF 0.1016 ±0.0508 (.004 ±.002) MSOP (MS16) 0213 REV A 238024f 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/LTC2380-24 33 LTC2380-24 TYPICAL APPLICATION LTC6362 Configured to Accept a ±10V Input Signal While Running from a Single 5V Supply with Digital Gain Compression Enabled in the LTC2380-24 VIN LTC6655-4.096 5V VOUT_F 4.096V VOUT_S 1k 1k V+ 1k 10V 0V –10V 47µF 333Ω VCM 10µF 8 3 1 IN+ 35.7Ω – V IN 35.7Ω 4 3.69V 6 REF VDD LTC2380-24 3300pF – 2 2.5V 6800pF 0.41V 5 + LTC6362 1k VCM 3.69V 6800pF – REF/DGC 238024 TA02 0.41V 333Ω RELATED PARTS PART NUMBER DESCRIPTION COMMENTS ADCs LTC2378-20/LTC2377-20/ 20-Bit, 1Msps/500ksps/250ksps, ±0.5ppm LTC2376-20 INL Serial, Low Power ADC 2.5V Supply, ±5V Fully Differential Input, 104dB SNR, MSOP-16 and 4mm × 3mm DFN-16 Packages LTC2379-18/LTC2378-18/ 18-Bit, 1.6Msps/1Msps/500ksps/250ksps LTC2377-18/LTC2376-18 Serial, Low Power ADC 2.5V Supply, Differential Input, 101.2dB 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 LTC2377-16/LTC2376-16 Serial, Low Power ADC 2.5V Supply, Differential Input, 96.2dB SNR, ±5V Input Range, DGC, Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages LTC2369-18/LTC2368-18/ 18-Bit, 1.6Msps/1Msps/500ksps/250ksps LTC2367-18/LTC2364-18 Serial, Low Power ADC 2.5V Supply, Pseudo-Differential Unipolar Input, 96.5dB SNR, 0V to 5V Input Range, Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages LTC2370-16/LTC2368-16/ 16-Bit, 2Msps/1Msps/500ksps/250ksps LTC2367-16/LTC2364-16 Serial, Low Power ADC 2.5V Supply, Pseudo-Differential Unipolar Input, 94dB SNR, 0V to 5V Input Range, Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages DACs LTC2757 18-Bit, Single Parallel IOUT SoftSpan™ DAC ±1LSB INL/DNL, Software-Selectable Ranges, 7mm × 7mm LQFP-48 Package LTC2641 16-Bit/14-Bit/12-Bit Single Serial VOUT DAC ±1LSB INL /DNL, MSOP-8 Package, 0V to 5V Output LTC2630 12-Bit/10-Bit/8-Bit Single VOUT DACs SC70 6-Pin Package, Internal Reference, ±1LSB INL (12 Bits) LTC6655 Precision Low Drift Low Noise Buffered Reference 5V/4.906V/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/4.906V/3.3V/3V/2.5V/2.048V/1.25V, 5ppm/°C, 2.1ppm Peak-to-Peak Noise, MSOP-8 Package LT6237 Dual Rail-to-Rail Output ADC Driver 215MHz GBW, 1.1nV/√Hz, 3.5mA Supply Current LT6203 Dual 100MHz Rail-to-Rail Input/Output Low Noise Power Amplifier 1.9nV/√Hz, 3mA Maximum Supply Current, 100MHz Gain Bandwidth LTC6362 Low Power, Fully Differential Input/Output Amplifier/Driver Single 2.8V to 5.25V Supply, 1mA Supply Current, MSOP-8 and 3mm × 3mm DFN-8 Packages REFERENCES AMPLIFIERS 238024f 34 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC2380-24 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC2380-24 LT 1015 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2015