DAC1282 SBAS490 – DECEMBER 2011 www.ti.com LOW DISTORTION DIGITAL-TO-ANALOG CONVERTER FOR SEISMIC Check for Samples: DAC1282 FEATURES DESCRIPTION • • • The DAC1282 is a fully-integrated digital-to-analog converter (DAC) providing low distortion, digital synthesized voltage output suitable for testing of seismic equipment. The DAC1282 achieves very high performance in a small package with low power. Together, with the high-performance ADS1281 and ADS1282 analog-to-digital converters (ADCs), these devices create a measurement system that meets the exacting demands of seismic data acquisition equipment. 1 23 • • • • • • • • • • • • Single-Chip Test Signal Generator Buffered Voltage Output High Performance: – THD: –125 dB (G = 1/1 to 1/8) – SNR: 120 dB (413 Hz BW, G = 1/1) Analog and Digital Gain Control Output Frequency: 0.488 Hz to 250 Hz Sine, Pulse, and DC Modes Digital Data Input Mode Low On-Resistance Signal Switch Sync Input Power-Down Mode Analog Supply: 5 V or ±2.5 V Digital Supply: 1.8 V to 3.3 V Power: 38 mW Package: TSSOP-24 Operating Range: –50°C to +125°C The DAC1282 integrates a digital signal generator, a DAC, and an output amplifier providing sine wave, dc, and pulse output voltages. The output frequency is programmable from 0.5 Hz to 250 Hz and the magnitude is scaled by both analog and digital control. The analog gain is adjustable in 6-dB steps and the digital gain in 0.5-dB steps. The analog gain settings match those of the ADS1282 for testing at all gains with high resolution. The DAC1282 also provides pulse outputs. The pulse amplitude is user-programmed and then selected by the pin for precise timing. Custom output signals can be generated by applying an external bitstream pattern. APPLICATIONS • • • Energy Exploration Seismic Monitoring Systems High-Accuracy Instrumentation A signal switch can be used to connect the DAC output to sensors for THD and impulse testing. The switch timing is controlled by pin and by command. A SYNC pin synchronizes the DAC output to the analog-to-digital converter (ADC) sample interval. A power-down input disables the device, reducing power consumption to microwatts. DVDD VREF AVDD DAC1282 CLK SYNC CS DIN DOUT Serial Interface Digital Signal Generator VOUTP Voltage Output DAC VOUTN SCLK Switch In RESET/ PWDN Optional Bitstream Input SW/TD Switch Out DGND AVSS 1 2 3 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. SPI is a trademark of Motorola. All other trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2011, Texas Instruments Incorporated DAC1282 SBAS490 – DECEMBER 2011 www.ti.com This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. ORDERING INFORMATION For the most current package and ordering information see the Package Option Addendum at the end of this document, or see the TI web site at www.ti.com. RELATED PRODUCTS DESCRIPTION DEVICE High-resolution ADC ADS1281 High-resolution ADC with PGA ADS1282 Low-drift 5 V reference REF5050 ABSOLUTE MAXIMUM RATINGS (1) Over operating free-air temperature range, unless otherwise noted. DAC1282 MIN MAX UNIT AVDD to AVSS –0.3 +5.5 V AVSS to DGND –2.8 +0.3 V DVDD to DGND –0.3 +3.6 V mA –10 +10 AVSS – 0.3 AVDD + 0.3 Switch current –60 +60 Digital input voltage to DGND –0.3 DVDD + 0.3 V Operating temperature range –50 +125 °C Storage temperature range –60 +150 °C Input current continuous Analog input/output voltage Human body model (HBM) JEDEC standard 22, test method A114-C.01, all pins Charge device model (CDM) JEDEC standard 22, test method C101, all pins ESD ratings (1) 2 ±2000 ±500 V mA V V Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not implied. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com ELECTRICAL CHARACTERISTICS Minimum/maximum specifications are at TA = –40°C to +85°C. Typical specifications are at TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREF = 5 V, and DVDD = 3.3 V, unless otherwise noted. Refer to Figure 50. DAC1282 PARAMETER TEST CONDITIONS MIN TYP MAX UNIT ANALOG OUTPUT (VOUTP, VOUTN) Full-scale output voltage (1) ±VREF /2 × gain Gain = 1/1 to 1/64 Output common-mode voltage (2) Differential output impedance CLOAD Capacitive load RLOAD Resistive load V –0.1 V 1.6 Ω 2 nF Ω 100 Output current limit (3) ±60 High-Z output leakage TA = +25°C 2 TA = +85°C 50 mA nA DC PERFORMANCE (Excluding Pulse Mode) Gain error Gain = 1/1 Gain match Relative to gain = 1/1 Gain drift ±0.1 ±0.75 ±0.05 ±0.5 2 Offset ±(7/gain) + 50 Gain = 1/1 to 1/64 Offset drift % % ppm/°C ±(75/gain) + 300 ppm FSR (4) ppm FSR/°C 1.5 AC PERFORMANCE THD Total harmonic distortion (5) Gain = 1/1 –125 Gain = 1/2, 1/4, 1/8 –125 dB Gain = 1/16 –123 dB Gain = 1/32 –115 dB Gain = 1/64 –111 dB 120 dB Gain = 1/2 119 dB Gain = 1/4 117 dB Gain = 1/8 114 dB Gain = 1/16 110 dB Gain = 1/32 106 dB Gain = 1/64 100 Gain = 1/1 SNR Signal-to-noise ratio (6) Output frequency Digital gain PSR (1) (2) (3) (4) (5) (6) Power-supply rejection 0.5-dB steps AVDD, AVSS DVDD 60-Hz ac, gain = 1/8 116 –118 dB dB 0.4883 250 Hz Full mute 0 dB 85 dB 120 dB Full-scale differential output voltage: VOUT = (VOUTP – VOUTN) = ±VREF/2 × Gain. Gain is the DAC analog gain. Output common-mode voltage scales with analog supply voltage: VCOM = 0.48 × (AVDD – AVSS) + AVSS. Sink or source current limit of VOUTP and VOUTN. FSR – full-scale range = VREF × gain. THD = total harmonic distortion. THD is measured by the ADS1282, and is the sum of first nine harmonics using complementing gain. fOUT = 31.25 Hz, VOUT – 0.5 dBFS, no load. SNR = signal-to-noise ratio. SNR is measured by the ADS1282 over a 413-Hz bandwidth using complementing gain. fOUT = 31.25 Hz and VOUT – 0.5 dBFS. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 3 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com ELECTRICAL CHARACTERISTICS (continued) Minimum/maximum specifications are at TA = –40°C to +85°C. Typical specifications are at TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREF = 5 V, and DVDD = 3.3 V, unless otherwise noted. Refer to Figure 50. DAC1282 PARAMETER TEST CONDITIONS MIN TYP MAX UNIT PULSE MODE Output levels 31 steps, approximate 3 dB per step ±0.0195 ±0.1 Gain error Gain drift V % 3 ±0.5 Offset Offset drift Output noise (7) Slew rate Settling time ±2.5 ±0.75 0.1% final value ppm/°C ±3 mV 3 µV/°C 1.5 µVRMS 5 V/µs 25 µs 24 Bits DC MODE Resolution 100 µs Gain = 1/1 1.3 µVRMS Gain = 1/2 1.4 µVRMS Gain = 1/4 1.8 µVRMS Gain = 1/8 2.7 µVRMS Gain = 1/16 4.7 µVRMS Gain = 1/32 8.5 µVRMS Gain = 1/64 16 µVRMS Step response DC noise (8) DIGITAL DATA MODE Data clock rate fCLK/16 Ones-density full-scale modulation +FS and –FS, respectively Signal bandwidth –3 dB 25 Hz 75 8.2 % kHz REFERENCE VOLTAGE INPUT (VREF) Reference voltage, VREF = VREF – AVSS Reference input impedance 2.4 Operating Power-down 5 AVDD + 0.25 V 220 kΩ 10 MΩ SIGNAL SWITCH Signal range AVSS AVDD ±50 V Current Continuous Differential on-resistance VSWIN , VSWOUT = 0 V 2.8 Ω Differential on-resistance flatness VSWIN, VSWOUT = AVDD to AVSS 0.7 Ω On-resistance match between outputs VSWIN , VSWOUT = 0 V 0.04 Ω TA = +25°C ±0.1 TA = +85°C ±5 Off-leakage current (9) Off-isolation (10) mA nA 120 dB DIGITAL INPUT/OUTPUT (DVDD = 1.65 V to 3.6 V) VOH IOH = 1 mA VOL IOL = 1 mA 0.8 × DVDD V V VIH 0.8 × DVDD DVDD V VIL DGND 0.2 × DVDD V ±10 µA Input hysteresis 0.5 Input leakage fCLK 0.2 × DVDD CLK Input 1 4.096 V 4.225 MHz (7) (8) VOUT = 0 V. Pulse mode output noise is measured by the ADS1282, over a 413-Hz bandwidth using ADC gain = 1. VOUT = 0 V. DC noise is measured by the ADS1282, over a 413-Hz bandwidth using complementing gain. DC noise is referred to a 1.77-V full-scale ADC output. Divide output-referred noise by the ADC gain to yield input-referred noise. (9) Switch input or output voltage = AVDD – 0.5 V to AVSS + 0.5 V. (10) f = 31.25 Hz, 1.77 VRMS. Switch output loaded 2 x 10 kΩ to mid-supply range. 4 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com ELECTRICAL CHARACTERISTICS (continued) Minimum/maximum specifications are at TA = –40°C to +85°C. Typical specifications are at TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, fCLK = 4.096 MHz, VREF = 5 V, and DVDD = 3.3 V, unless otherwise noted. Refer to Figure 50. DAC1282 PARAMETER TEST CONDITIONS MIN TYP MAX UNIT POWER SUPPLY AVSS –2.6 0 V AVDD AVSS + 4.75 AVSS + 5.25 V DVDD 1.65 3.6 V 8.5 mA (11) Gain = 1/1, VOUT = 0 V AVDD, AVSS current DVDD current 7.4 Pulse mode, VOUT = 0 V 7 Shutdown 1 10 µA Operating 180 300 µA 1 10 µA Operating 38 44 mW Shutdown (12) 10 85 µW Shutdown (12) Power mA TEMPERATURE RANGE Specified temperature range –40 +85 °C Operating temperature range –50 +125 °C Storage temperature range –65 +150 °C (11) Analog supply current scales with gain as follows: IAVDD and IAVSS = 0.016 × VREF × (44 × Gain + 1) + 3.8 (mA). (12) Digital inputs stopped and maintained at VIH or VIL level. THERMAL INFORMATION DAC1282IPW THERMAL METRIC (1) PW (TSSOP) UNITS 24 PINS θJA Junction-to-ambient thermal resistance 78.3 θJCtop Junction-to-case (top) thermal resistance 12.1 θJB Junction-to-board thermal resistance 33.8 ψJT Junction-to-top characterization parameter 0.3 ψJB Junction-to-board characterization parameter 33.5 θJCbot Junction-to-case (bottom) thermal resistance N/A (1) °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 5 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com PIN CONFIGURATION PW PACKAGE TSSOP-24 (TOP VIEW) CS 1 24 AVDD SCLK 2 23 AVSS DIN 3 22 CAPP DOUT 4 21 VOUTP DVDD 5 20 SWINP DGND 6 19 SWOUTP CLK 7 18 SWOUTN 8 17 SWINN 9 16 VOUTN 10 15 CAPN DGND 11 14 AVSS VREF 12 13 AVDD SW/TD SYNC RESET/PWDN DAC1282 Terminal Functions 6 PIN NAME PIN # FUNCTION AVDD 13, 24 Analog supply DESCRIPTION Analog positive power supply AVSS 14 Analog supply Analog negative power supply, reference ground AVSS 23 Analog supply Analog negative power supply CAPN 15 Analog External capacitor connected to VOUTN CAPP 22 Analog External capacitor connected to VOUTP CS 1 Digital input Serial port chip select Master clock 4.096 MHz CLK 7 Digital input DGND 6 Ground Key digital ground DGND 11 Ground Digital ground DIN 3 Digital input DOUT 4 Digital output Serial port data input Serial port data output DVDD 5 Digital supply Digital power supply: 1.65 V to 3.6 V RESET/PWDN 10 Digital input Reset/power-down input SCLK 2 Digital input Serial port shift clock SW/TD 8 Digital input Switch control input or bitstream input SWINN 17 Analog I/O Switch negative input SWINP 20 Analog I/O Switch positive input SWOUTN 18 Analog I/O Switch negative output SWOUTP 19 Analog I/O Switch positive output Synchronize input SYNC 9 Digital input VOUTN 16 Analog output Negative voltage output VOUTP 21 Analog output Positive voltage output VREF 12 Analog input Reference voltage input Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com SPI TIMING CHARACTERISTICS t SPWH t SCLK t CSH CS t SPWL t CSSC t SCCS SCLK t DIST DIN B7 B6 B5 B4 B3 B2 B1 t DIHD B0 t DOPD B7 DOUT t DOHD t CSDOD t CSDOZ Figure 1. Serial Interface Timing TIMING REQUIREMENTS: SERIAL INTERFACE TIMING At TA = –40°C to +85°C and DVDD = 1.65 V to 3.6 V, unless otherwise noted. SYMBOL (1) (2) (3) DESCRIPTION (1) MIN MAX UNIT tCSSC CS low to first SCLK: setup time 30 ns tSCLK SCLK period 120 ns tSPWH SCLK pulse width: high 50 ns tSPWL SCLK pulse width: low (2) tDIST Valid DIN to SCLK high: setup time 40 ns tDIHD Valid DIN to SCLK high: hold time 20 ns 50 ns 218 (3) tCLK tDOPD SCLK low to valid new DOUT: propagation delay 40 ns tDOHD SCLK low to DOUT invalid: hold time 0 ns tCSDOD CS low to DOUT driven: propagation delay (3) 40 ns tCSDOZ CS high to DOUT Hi-Z: propagation delay 20 ns tCSH CS high pulse 50 ns tSCCS Last SCLK falling edge to CS high 0 ns CS can be tied low. Holding SCLK low longer than 218 fCLK cycles resets the SPI interface. DOUT load = 20 pF || 100 kΩ to DGND. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 7 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com TYPICAL CHARACTERISTICS At TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, DVDD = 3.3 V, fCLK = 4.096 MHz, and VREF = 5 V, unless otherwise noted. OUTPUT SPECTRUM GAIN = 1/1 OUTPUT SPECTRUM GAIN = 1/2 0 0 Amplitude (dB) −40 −60 −80 −100 −120 −140 −40 −60 −80 −100 −120 −140 −160 −160 −180 −180 −200 0 50 Gain = 1/2 4k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −125.6 dB SNR = 119.0 dB −20 Amplitude (dB) Gain = 1/1 4k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −125.8 dB SNR = 120.1 dB −20 −200 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 0 50 Figure 2. Figure 3. OUTPUT SPECTRUM GAIN = 1/4 OUTPUT SPECTRUM GAIN = 1/8 0 0 Amplitude (dB) −40 −60 −80 −100 −120 −140 −40 −60 −80 −100 −120 −140 −160 −160 −180 −180 0 50 Gain = 1/8 4k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −125.4 dB SNR = 114.5 dB −20 Amplitude (dB) Gain = 1/4 4k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −125.9 dB SNR = 117.8 dB −20 −200 −200 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 0 50 Figure 4. OUTPUT SPECTRUM GAIN = 1/16 OUTPUT SPECTRUM GAIN = 1/32 0 Amplitude (dB) −40 −60 −80 −100 −120 −140 −40 −60 −80 −100 −120 −140 −160 −160 −180 −180 0 50 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 Gain = 1/32 8k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −116.7 dB SNR = 105.7 dB −20 Amplitude (dB) Gain = 1/16 8k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −126.1 dB SNR = 109.8 dB −20 −200 0 Figure 6. 8 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 Figure 5. 0 −200 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 50 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 Figure 7. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com TYPICAL CHARACTERISTICS (continued) At TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, DVDD = 3.3 V, fCLK = 4.096 MHz, and VREF = 5 V, unless otherwise noted. OUTPUT SPECTRUM GAIN = 1/64 GAIN ERROR vs TEMPERATURE 2000 0 Gain = 1/64 8k FFT Vo = 31.25 Hz, −0.5 dBFS THD = −112.8 dB SNR = 100.1 dB Amplitude (dB) −40 −60 1750 1500 Gain Error (ppm) −20 −80 −100 −120 −140 1000 750 500 −160 Gain = 1/1 Gain = 1/2 Gain = 1/4 250 −180 −200 1250 0 50 0 −55 100 150 200 250 300 350 400 450 500 Frequency (Hz) G000 −35 −15 Figure 8. GAIN ERROR HISTOGRAM 25 45 65 Temperature (°C) 85 105 125 G000 GAIN MATCH HISTOGRAM 20 Gain = 1/1 30 units All gains relative to gain = 1/1 30 units 15 Occurrences (%) 15 10 10 5 0 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 5 −4000 −3600 −3200 −2800 −2400 −2000 −1600 −1200 −800 −400 0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 Occurrences (%) 5 Gain = 1/64 Pulse Mode Figure 9. 20 Gain Error (ppm) Absolute Gain Match (ppm) G000 Figure 10. OFFSET vs TEMPERATURE OFFSET HISTOGRAM 25 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 250 0 −250 20 15 10 5 −35 −15 5 25 45 65 Temperature (°C) 85 105 125 G000 0 −400 −360 −320 −280 −240 −200 −160 −120 −80 −40 0 40 80 120 160 200 240 280 320 360 400 −500 −750 −55 Gain = 1/1 30 units Gain = 1/64 Pulse Mode Occurrences (%) 500 G000 Figure 11. 750 Offset (ppm) Gain = 1/8 Gain = 1/16 Gain = 1/32 Offset Error (ppm) Figure 12. G000 Figure 13. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 9 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com TYPICAL CHARACTERISTICS (continued) At TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, DVDD = 3.3 V, fCLK = 4.096 MHz, and VREF = 5 V, unless otherwise noted. THD vs TEMPERATURE SNR vs TEMPERATURE 125 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 −105 Gain = 1/16 Gain = 1/32 Gain = 1/64 Signal−to−Noise Ratio (dB) Total Harmonic Distortion (dB) −100 −110 −115 −120 −125 −130 −55 120 115 110 105 100 95 −35 −15 5 25 45 65 Temperature (°C) 85 105 90 −55 125 Gain = 1/1 Gain = 1/2 Gain = 1/4 −35 −15 Gain = 1/8 Gain = 1/16 Gain = 1/32 5 G000 Figure 14. THD vs SIGNAL FREQUENCY Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 Signal−to−Noise Ratio (dB) Total Harmonic Distortion (dB) 125 G000 SNR vs SIGNAL FREQUENCY −115 −120 −125 125 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 120 115 110 105 100 1 10 100 Signal Frequency (Hz) 95 0.1 1000 1 G000 10 100 Signal Frequency (Hz) Figure 16. THD vs SIGNAL AMPLITUDE G000 SNR vs SIGNAL AMPLITUDE 120 −40 −60 Signal−to−Noise Ratio (dB) Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 −20 −80 −100 −120 −140 −120 1000 Figure 17. 0 Total Harmonic Distortion (dB) 105 130 −130 0.1 −100 −80 −60 −40 Signal Amplitude (dB) −20 0 100 80 60 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 40 20 0 −120 G000 Figure 18. 10 85 Figure 15. −105 −110 25 45 65 Temperature (°C) Gain = 1/64 −100 −80 −60 −40 Signal Amplitude (dB) −20 0 G000 Figure 19. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com TYPICAL CHARACTERISTICS (continued) At TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, DVDD = 3.3 V, fCLK = 4.096 MHz, and VREF = 5 V, unless otherwise noted. THD vs MASTER CLOCK FREQUENCY SNR vs MASTER CLOCK FREQUENCY 135 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 −95 −100 −105 −110 −115 −120 −125 125 Gain = 1/8 Gain = 1/16 Gain = 1/32 120 115 110 105 1 1.5 2 2.5 3 CLK (MHz) 3.5 4 95 4.5 1 1.5 2 2.5 3 Clock (MHz) G000 Figure 20. THD vs REFERENCE VOLTAGE 4.5 G000 SNR vs REFERENCE VOLTAGE Gain = 1/1 Gain = 1/2 Gain = 1/4 −95 −100 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 Gain = 1/1 Gain = 1/2 Gain = 1/4 130 Signal−to−Noise Ratio (dB) Total Harmonic Distortion (dB) 4 135 −105 −110 −115 −120 −125 125 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 120 115 110 105 100 −130 2 2.5 3 3.5 4 4.5 Reference Voltage (V) 5 95 2.5 5.5 3 3.5 4 4.5 Reference Voltage (V) G000 Figure 22. THD HISTOGRAM 30 G000 POWER-SUPPLY CURRENT vs TEMPERATURE Gain = 1/1...1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 30 Units 7 25 20 15 10 6 5 4 3 2 1 5 0 −130 5.5 8 Quiescent Current (mA) 35 5 Figure 23. 40 Occurrences (%) 3.5 Figure 21. −90 −135 Gain = 1/64 100 −130 −135 Gain = 1/1 Gain = 1/2 Gain = 1/4 130 Signal−to−Noise Ratio (dB) Total Harmonic Distortion (dB) −90 −125 −120 −115 −110 Total Harmonic Distortion (dB) −105 0 −55 G000 Figure 24. Gain = 1/1 Gain = 1/2 Gain = 1/4 −35 −15 Gain = 1/8 Gain = 1/16 Gain = 1/32 5 25 45 65 Temperature (°C) Gain = 1/64 DVDD 85 105 125 G000 Figure 25. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 11 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com TYPICAL CHARACTERISTICS (continued) At TA = +25°C, AVDD = +2.5 V, AVSS = –2.5 V, DVDD = 3.3 V, fCLK = 4.096 MHz, and VREF = 5 V, unless otherwise noted. THD vs RESISTIVE LOAD SWITCH THD vs RESISTIVE LOAD −50 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 −100 −105 Gain = 1/16 Gain = 1/32 Gain = 1/64 Total Harmonic Distortion (dB) Total Harmonic Distortion (dB) −95 −110 −115 −120 −125 −130 −135 10 100 1000 10000 Load Resistance (Ω) 100000 −70 −80 −90 −100 −110 −120 −130 1000000 Gain = 1/1 Gain = 1/2 Gain = 1/4 Gain = 1/8 Gain = 1/16 Gain = 1/32 Gain = 1/64 −60 10 100 1000 10000 100000 Switch Output Load Resistance (Ω) G000 Figure 26. DIGITAL GAIN LINEARITY SWITCH ON-RESISTANCE vs SIGNAL VOLTAGE Switch Differential On−Resistance (Ω) 5 Digital Gain Error (dB) 0.75 0.5 0.25 0 −0.25 −0.5 −0.75 −1 −120 −100 −80 −60 −40 Digital Attenuation (dB) −20 4 3 2 TA = −40°C TA = +25°C TA = +85°C 1 0 −2.5 0 −2 G000 −1.5 −1 −0.5 0 0.5 1 1.5 Switch Input/Output Voltage (V) 2 2.5 G000 Figure 28. Figure 29. SWITCH ON-RESISTANCE HISTOGRAM SWITCH ON-RESISTANCE MATCH vs TEMPERATURE 0.1 30 Switch On−Resistance Match (Ω) 30 units 25 Occurrences (%) G000 Figure 27. 1 20 15 10 5 2.75 2.76 2.77 2.78 2.79 2.8 2.81 2.82 2.83 2.84 2.85 2.86 2.87 2.88 2.89 2.9 2.91 2.92 2.93 2.94 2.95 0 Switch Differential On Resistance (Ω) 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 −55 −35 −15 5 25 45 65 Temperature (°C) 85 105 125 G000 G000 Figure 30. 12 1000000 Figure 31. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com OVERVIEW The DAC1282 is a single-chip, digital-to-analog converter (DAC) that self-generates low-distortion sine-wave and pulse-output signals for the demanding testing requirements of seismic recording equipment. Figure 32 shows the block diagram of the DAC1282. The DAC1282 requires two supply voltages: analog and digital. The analog supply can be single 5 V or bipolar ±2.5 V. The digital supply range is 1.65 V to 3.6V. The output signal common-mode voltage is regulated to 100 mV below the midpoint of the analog power-supply voltage. An internal power-on reset (POR) circuit resets the DAC on power-up. An SPI™-compatible serial interface is used to access the DAC1282 registers for device configuration and control. The configuration registers can be read back by clocking the data out on the DOUT pin. The DAC1282 voltage output is fully differential and is taken out on the VOUTP/VOUTN pins. The CAPP/CAPN pins connect to external filter capacitors to reduce the output noise. The reference input voltage sets the DAC1282 full-scale output. The DAC reference voltage is applied between the VREF and AVSS pins. The DAC is optimized to operate with a 5-V reference. The sine-wave generator is programmable by registers to set the sine frequency and amplitude. The frequency range is programmable from 0.4883 Hz to 250 Hz. The output level is controlled by both analog gain (in 6-dB steps), and digital gain (in 0.5-dB steps). DVDD VREF Analog Gain Control CLK RESET/PWDN SYNC CS SCLK DIN Current Generator Synchronization Sine Wave Generator AVDD Digital Modulator CAPP VOUTP Main DAC Buffer VOUTN Serial Interface 24-Bit DC Register DOUT CAPN Pulse Registers Pulse DAC SWINP SYNC Differential Switch Switch Control/Bitstream Input SW/TD DAC1282 DGND SWINN SWOUTN SWOUTP AVSS Figure 32. DAC1282 Block Diagram The digital modulator takes the output from the sine-wave generator or the 24-bit dc register to generate the ones-density bitstream. The bitstream drives the main DAC. Optionally, ones-density data can be input to drive the DAC directly, bypasses the digital signal generator. The main DAC develops a differential output current that is converted to a differential output voltage by an internal current-to-voltage (I/V) amplifier. The output range is set by analog gain that scales the DAC current generator. The output amplifier provides current limit protection. The dc mode is programmed by a 24-bit register and is used to provide a dc output. The dc mode also has programmable ranges controlled by the analog gain control. In Pulse mode, a fast-response, 5-bit pulse DAC is used to provide 31 preset dc levels. The levels span over the available output ranges. The pulse DAC is optimized to provide fast response with short output rise times. The pulse DAC is triggered by the SYNC pin for precision control of the pulse time. The DAC1282 includes a low distortion differential output switch. The output switch can connect the DAC1282 output to sensors for THD and impulse testing. The switch is controlled by either pin or command, thus allowing precise switch timing. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 13 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com The SYNC input synchronizes the output signal to a known time reference. In sine mode, SYNC resets the sine wave to the zero crossing. In Pulse mode, SYNC selects one of two user-programmed dc levels. The RESET/PWDN pin powers down the device when low. When RESET/PWDN is released high, the DAC1282 is reset. The SW/TD input is dual function. In digital data mode, the pin is the ones-density data input. In the other modes, SW/TD controls the opening/closing of the switch. Figure 33 shows the main details of the main DAC. The main DAC provides the digital-to-analog conversion by filtering the ones-density digital data. In operation, the current generator establishes the range current that is mirrored to a multi-tap, current-steering filter stage. The current generator is controlled by the analog gain control register that scales the weight of the tap currents to one of seven ranges (0 dB to –36 dB). The current-steering stage switches the tap currents to the positive or negative current summing nodes, as the digital input is sampled. A higher ones-density directs an increasing average current to one node than the other, thus increasing the differential current. The differential current is converted to differential voltage by the internal I/V converter stage. The common-mode current sources balance the current at the amplifier summing node. VREF AVDD Sine Wave Table ... Current Taps Current Generator Digital Modulator Amplifier Summing Nodes Tap Control Digital Data Mux SW/TD Reset SYNC CLK Reset Common-Mode Current Reset D 4-Bit Counter CLK/16 ... D AVSS Figure 33. Main DAC Block Diagram 14 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com SIGNAL OUTPUT (VOUTP, VOUTN) As shown in Figure 34, the DAC provides a differential voltage (VDIFF = VOUTP – VOUTN) on pins VOUTP and VOUTN. The output common-mode voltage (VCOM) is regulated to 100 mV below the midpoint of the analog supply (AVDD – AVSS). Each signal output swings above and below the common-mode voltage. Best performance is realized when the DAC output is used differentially. In power-down mode, the outputs enter a high-impedance, 3-state mode. VOUTP VCOM + VDIFF/2 V COM VCOM - VDIFF/2 VCOM + VDIFF/2 DAC1282 V COM VOUTN VCOM - VDIFF/2 NOTE: VDIFF = VOUTP – VOUTN = ±2.5 V × Gain (VREF = 5 V). VCOM = –0.1 V (±2.5-V supplies) or 2.4 V (5-V supply). Figure 34. DAC Output Signal The DAC output buffer is rated to drive up to a 2-nF capacitive load (maximum) and a 100-Ω resistive load (minimum). However, degradation of THD performance results in resistive loads less than 1 kΩ, as shown in Figure 26 The internal digital modulator generates the signal to drive the DAC. The modulator shapes the in-band noise to high frequency and the frequency-shaped noise is present on the DAC output. However, the high frequency DAC output noise is rejected by the digital filter of the ADC and does not affect system performance. DAC MODES The DAC1282 has four operational modes of: sine, dc, pulse, and external digital data input. These modes are programmed by the MODE[1:0] bits in the GANMOD register, as shown in Table 1. Table 1. DAC Modes MODE[1:0] BITS DAC MODE 00 Sine 01 DC 10 Digital data 11 Pulse Sine Mode In sine mode, the DAC1282 provides a sine-wave output. An internal signal generator develops the sine-wave signal. The M[3:0], N[7:0], and FREQ register bits program the output frequency. The frequency range is programmable from 0.4883 Hz to 250 Hz, as shown in Equation 1. (1) Output Frequency (Hz) = 250 2 FREQ M[3:0] + 1 x N[7:0] + 1 where: M[3:0] ≤ N[7:0] (1) fCLK = 4.096 MHz. The signal frequency scales with fCLK. (1) Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 15 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com Table 2 lists values of registers M and N for selected output frequencies. Table 2. Register Output Frequencies SIGNAL FREQUENCY (Hz) (1) (1) M[3:0] REGISTER BITS N[7:0] REGISTER BITS FREQ BIT 0.48828125 0000 1111 1111 1 0.9765625 0000 1111 1111 0 1.953125 0000 0111 1111 0 3.90625 0000 0011 1111 0 7.8125 0000 0001 1111 0 15.625 0000 0000 1111 0 31.25 0000 0000 0111 0 50 0000 0000 0100 0 55 1010 0011 0001 0 60 0101 0001 1000 0 62.5 0000 0000 0011 0 100 1001 0001 1000 0 125 0000 0000 0001 0 250 0000 0000 0000 0 fCLK = 4.096M Hz. The signal frequency scales with fCLK. When the M or N registers are updated, the sine wave resets to the zero-crossing point. The sine wave can also be reset to the zero-crossing point by taking the SYNC pin high; see the SYNC section. The amplitude of the sine-wave output is determined by analog and digital gains. The analog gain increments are 6 dB, from 0 dB to –36 dB, and are programmed by the GAIN[2:0] register bits. Table 3 lists the analog gains. Table 3. Analog Gain ANALOG GAIN (1) (2) 16 ANALOG GAIN (dB) (1) DIFFERENTIAL RANGE (V) (2) GAIN[2:0] REGISTER BITS 1/1 0 ±2.5 000 1/2 –6 ±1.25 001 1/4 –12 ±0.625 010 1/8 –18 ±0.312 011 1/16 –24 ±0.156 100 1/32 –30 ±0.078 101 1/64 –36 ±0.039 110 Relative to 1.77 VRMS full-scale. VREF = 5 V, digital gain = 0 dB. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com The digital gain resolution is in 0.5-dB increments, from 0 dB to full mute and is programmed by the SINEG[7:0] register bits. Table 4 lists the digital gain setting. Equation 2 is the amplitude setting in sine mode. Sine Amplitude (dB) = Analog Gain (dB) + Digital Gain (dB) (2) Best SNR, for a given signal level, is achieved by reducing the analog gain while maximizing the digital gain. Table 4. Sine Mode Digital Gain SINE MODE DIGITAL GAIN (dB) SINEG[7:0] REGISTER BITS 0 0000 0000 –0.5 0000 0001 –1.0 0000 0010 — — –119.5 1110 1111 Full mute 1111 0000 Full mute 1111 xxxx Full mute 1111 1111 DC Mode The DAC1282 provides a dc output mode with 24-bit available resolution. The output level is determined by the analog gain and the 24-bit dc registers. The GAIN[2:0] register bits set the analog gain (see Table 3). The DCG[23:0] register bits set the 24-bit level over the selected analog range. Table 5 lists the digital gain settings in dc mode. Table 5. DC Mode Digital Gain Settings DIFFERENTIAL OUTPUT VOLTAGE (V) (1) (1) DCG[23:0] REGISTER BITS +2.5 x Gain 7FFFFFh +1.25 x Gain 3FFFFFh 0 0 –1.25 x Gain C00000h –2.5 x Gain 800001h VREF = 5 V. Ideal output voltage excluding gain, offset, linearity and noise errors.. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 17 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com Pulse Mode In pulse mode, a fast responding, 5-bit pulse DAC is used to generate the output. The pulse DAC is designed to approximate a linear-in-dB output function, allowing the generation of pulse test signals across all ranges. Two registers are used to preset the DAC output. The SYNC pin is used to select one of the two registers. When SYNC is low, the PULSA register value drives the DAC; when SYNC is high, the PULSB register value drives the DAC. The pulse registers can be programmed to yield differential outputs from –2.5 V to +2.5 V. Note that the pulse levels scale with VREF and are independent of the analog gain settings. Table 6 lists the programmable range of the pulse A and pulse B registers. Table 6. Pulse Register Values PULSA[4:0], PULSB[4:0] OUTPUT (V) (1) PULSA[4:0], PULSB[4:0] +2.50 01111 –0.020 11111 +1.88 01110 –0.029 11110 +1.25 01101 –0.039 11101 +0.938 01100 –0.058 11100 +0.625 01011 –0.078 11011 +0.469 01010 –0.117 11010 +0.312 01001 –0.156 11001 +0.234 01000 –0.234 11000 +0.156 00111 –0.312 10111 +0.117 00110 –0.469 10110 +0.078 00101 –0.625 10101 +0.058 00100 –0.938 10100 +0.039 00011 –1.25 10011 +0.029 00010 –1.88 10010 +0.020 00001 –2.50 10001 0 00000 OUTPUT (V) (1) (1) VREF = 5 V. Ideal pulse mode differential output, values are rounded and exclude noise, offset, gain, and linearity errors. Note that when pulse testing the ADC, the ADC digital filter time domain response has characteristic overshoot and ringing. As a result of the ADC filter overshoot, input levels close to ADC full scale may cause clipping of the ADC output code. Digital Data Mode In digital data mode, the DAC internal signal generator is bypassed and the DAC is driven instead by applying a bitstream input. Arbitrary DAC output waveforms can be generated by application of custom digital data patterns. The data format in this mode is ones-density modulated input at CLK/16 data rate (256 kHz). The input is applied to the SW/TD input pin. The DAC1282 output in digital data mode is defined in Equation 3. Digital Data Mode Differential Output = VOUTP – VOUTN = VREF/2 × Gain × (TD – 50%)/25% where: VREF is 5-V nominal, Gain is the analog gain (1/1 to 1/64), TD is the bitstream ones-density from 25% to 75%. 18 Submit Documentation Feedback (3) Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com The DAC1282 filters the digital data (bitstream) input providing a voltage output proportional to the bitstream ones-density. The GAIN[2:0] register sets the analog gain in 6-dB steps, from 0 dB to –36 dB (1/1 to 1/64); see the SYNC section for the external timing requirements. Table 7 lists several values of the external bitstream input. Table 7. External Bitstream Input (1) ONES-DENSITY BITSTREAM (%) VOUTP – VOUTN (V) (1) 25 –2.5 × Gain 37.5 –1.25 × Gain 50 0 62.5 +1.25 × Gain 75 +2.5 × Gain VREF = 5 V. Gain is the analog gain, programmable from 1/1 to 1/64 (0 dB to –36 dB). REFERENCE VOLTAGE (VREF) The DAC1282 requires an external reference for operation. Although reference voltage as low as 2.5 V can be used, best SNR is achieved with a 5-V reference. The reference input is defined as the voltage difference between VREF and AVSS (that is, VREF = VREF – AVSS). The DAC1282 output scales with VREF; consequently, reference noise or drift appears on the DAC output. Excessive reference noise may lead to degraded SNR. A low-drift and low-noise reference is recommended. Connect the external reference ground pin directly to the AVSS pins using a star connector to AVSS pin 14. Star connection minimizes the possibility of power-supply crosstalk. Also, connect a 0.1-µF capacitor close to the VREF and AVSS terminals to reduce noise susceptibility. Figure 35 shows the reference connection. The reference input impedance is 220 kΩ. In power-down the switch is off, resulting in very high input impedance. For single-supply applications, connect AVSS to a clean analog ground point. +V VREF 5V Reference Internal Circuitry 220 kΩ 0.1 µF -2.5 V (1) Power-down Switch AVSS (14) AVSS (23) (1) Recommended bypass capacitor. Figure 35. Reference Input Connection Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 19 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com OUTPUT FILTER (CAPP, CAPN) The CAPP and CAPN pins are the connections for two external capacitors, one capacitor connects to CAPP and VOUTP and the other capacitor connects to CAPN and VOUTN. The capacitors are required to filter the DAC sampling noise. The capacitor values are 1 nF; capacitors with low voltage coefficients should be used (C0G ceramic or film). As seen in Figure 36, the external capacitors form an analog low-pass filter with the internal feedback resistors. After step changes to the data in the sine, dc, and digital data modes, the settling of the DAC and the analog filter is 100-µs typical, as shown in Figure 46. In pulse mode, the filter is internally disabled, yielding shorter settling time. CAPP 2k 1 nF VOUTP Current DAC Output Amplifier VOUTN 2k 1 nF CAPN Figure 36. Output Filter 20 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com OUTPUT SWITCH (SWINP, SWINN, SWOUTP, SWOUTN) The DAC1282 has an integrated output switch. The switch can be used to route the DAC output signal to a sensor for pulse, THD, and common-mode testing. The switch has low on-resistance and matched elements to minimize signal distortion. The switch input voltage range extends to the analog power supply. The switch is controlled by three register bits, SW[2:0], and is also controlled by the SW/TD input pin. The switch integrates break-before-make operation when the register or the SW/TD input control is changed. The SW/TD input can be used to force the switch open for precise timing control of sensor impulse testing; see the Switch Control/DAC Data Input (SW/TD) section. Figure 37 and Table 8 describe the switch operation. S1 SWINP SWOUTP S2 S5 S3 SWINN SWOUTN S4 Figure 37. DAC1282 Signal Switch Note that when the DAC is in power-down mode, the switch is forced open. As shown in Figure 29, the switch on-resistance varies with the switch signal level. When the switch is used to route the signal and a resistive load is connected to the switch output, the switch on-resistance variations interact with the load resistance and cause the THD to degrade. Figure 27 illustrates the dependence of THD versus switch load resistance. The dependence of THD data was taken with a full-scale signal. Table 8. Switch Connections DESCRIPTION PIN CONNECTIONS SWITCHES CLOSED SW[2:0] REGISTER BITS Open (default) Open None 000 Differential SWINP to SWOUTP and SWINN to SWOUTN S1, S3 001 Differential reverse SWINP to SWOUTN and SWINN to SWOUTP S2, S4 010 Common-mode positive SWINP to SWOUTP and SWOUTN S1, S2 011 Common-mode negative SWINN to SWOUTP and SWOUTN S3, S4 100 Single-ended positive SWINP to SWOUTP S1 101 Single-ended negative SWINN to SWOUTN S3 110 Output short SWOUTP to SWOUTN S5 111 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 21 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com CLOCK INPUT (CLK) The CLK pin is the master clock input to the DAC1282, nominally 4.096 MHz. As with any high-performance data converter, a high-quality clock source is essential. A crystal oscillator or low-jitter PLL clock source is recommended. Make sure to avoid ringing on the input by keeping the trace short and source-terminating (typically 50 Ω). See the CLK specifications shown in Figure 38 and Table 9. t CLK t CPWL t CPWH CLK Figure 38. CLK Timing Requirements Table 9. Requirements for Figure 38 SYMBOL tCLK tCPWH, L DESCRIPTION MIN MAX UNIT CLK period 235 1000 ns CLK pulse width high or low 95 900 ns SWITCH CONTROL/EXTERNAL DIGITAL INPUT (SW/TD) SW/TD is a multi-function digital input pin. The SW/TD function depends on the mode of operation. SW Function In sine, dc, and pulse mode, SW/TD controls the output switch. When SW/TD is low, all switches are forced open, overriding the switch register setting (SW[2:0]). When SW/TD is high, the switch is transparent to the value of register setting. In power-down mode, the switch is forced open. TD Function In digital input mode, SW/TD is the signal input used to drive the DAC. The data input are modulated by ones-density and are clocked in by the master clock (CLK). When the ones-density is 75% (that is, on average, three out of four bits are '1'), the differential output voltage is at the positive maximum value. When the ones-density is 25% (that is, on average, three out of four bits are '0'), the differential output voltage is at the negative maximum value. When the ones-density is 50% (on average, an equal number of '0's and '1's), the differential output is zero. SW/TD is sampled by the DAC1282 at the rate of CLK/16. Therefore, the sampling can have ±8 CLK periods of uncertainty. SYNC can be used to eliminate the uncertainty by synchronizing the phase of SW/TD to the desired CLK cycle. Synchronizing the digital input results in a consistent phase of the output signal; see the SYNC section. The output range is set by the analog gain bits, GAIN[2:0]; see Table 3. Equation 3 describes the DAC output versus the bitstream input ones-density. Make sure to avoid ringing on the input by keeping the trace short. In some cases, source-terminating resistors may be necessary (20 Ω to 50 Ω). 22 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com SYNC SYNC is a digital input used to synchronize the DAC1282 output. In the digital data mode, the DAC input is a ones-density bitstream. In this mode, the SYNC pin synchronizes the sampling of SW/TD digital data to the desired master clock cycle (CLK). When SYNC is low or high, the DAC operates normally. When SYNC is taken from low to high, the DAC output is reset to zero and the sample instant of SW/TD is reset to the eighth rising CLK edge that follows. The SW/TD is then regularly sampled on subsequent 16 CLK intervals. After synchronization, the DAC output is not settled and achieves full settling 400 CLK periods later, as shown in Figure 39. t SW/TD t TCSU CLK 2 1 8 9 12 24 400 Next SW/TD Sample SW/TD Sample SW/TD t SCSU SYNC t CTHD t STDAT t SYLW (Initial Output Update) (Output Reset) (Output Settled) Output t TSOP t SETL Figure 39. Digital Data Mode Synchronization Table 10. Timing Characteristics for Figure 39 (1) SYMBOL (1) DESCRIPTION MIN TYP UNIT tSCSU SYNC high to CLK high setup time 30 ns tTCSU SW/TD to CLK high setup time 30 ns tCTHD CLK high to SW/TD hold time 10 ns tSYLW SYNC low pulse width 2 tCLK tSTDAT CLK high after SYNC high to SW/TD sample time 8 tCLK tTSOP SW/TD sample to output update 4 tCLK tSW/TD SW/TD period 16 tCLK tSETL SYNC high to fully-settled output 400 tCLK DVDD = 1.65 V to 3.6 V. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 23 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com In sine mode, the SYNC rising edge resets the DAC output to differential 0 V (sine-wave zero-crossing point). When SYNC is high or low, the output is unaffected. When SYNC is taken from low to high, the output resets on the following CLK rising edge. SYNC must be pulsed low for a minimum of 2 CLK cycles. The SYNC input can be applied simultaneous to the DAC and the ADS1282 (ADC in pulse-sync mode). To synchronize the DAC, observe SYNC to the CLK timing requirements shown in Figure 40. That is, the SYNC rising edge should be applied before the set-up time or after the hold time specifications. If the SYNC timing requirement is not met, the DAC may synchronize with one clock cycle timing error. t SCSU t CSHD CLK t SYLO SYNC Figure 40. Sine Mode Synchronization Table 11. Timing Characteristics for Figure 40 (1) SYMBOL (1) DESCRIPTION MIN UNIT tSYLO SYNC pulse width low 2 tCLK tSCSU SYNC rising edge to CLK rising edge setup time 30 ns tCSHD CLK rising edge to SYNC rising edge hold time 10 ns DVDD = 1.65 V to 3.6 V. In pulse mode, the SYNC pin selects one of two pre-programmed pulse levels. The pulse levels are programmable from +2.5 V to –2.5 V in approximately 3-dB steps by pulse level registers PULSA and PULSB. When SYNC is low, the value of the PULSA register drives the DAC; when SYNC is high, the value of the PULSB register is the code of the DAC, as shown in Figure 41. When the SYNC pin is changed, the DAC output updates immediately to the new code. Output PULSA PULSB PULSA SYNC Figure 41. SYNC Operation in Pulse Mode 24 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com RESET/PWDN The RESET/PWDN is a digital input used to power-down and reset the DAC1282. To power-down the DAC, take the pin low. In power-down mode, the power consumption is reduced to a device leakage level (see the Electrical Characteristics table). The signal output and digital pin DOUT enters 3-state and the output switch is driven off. Note that the digital inputs must remain defined as either logic low or logic high; do not float the inputs. Disable the CLK input to minimize leakage. To exit the power-down state, take the pin high. The DAC1282 is reset after power-down mode is exited. The DAC1282 is reset by taking the RESET/PWDN pin low for a minimum of two fCLK cycles and is then taken back high. The DAC1282 is held in reset for 2 fCLK cycles; after this time, DAC communications may begin, as shown in Figure 42 and Table 12. CLK RESET/PWDN t RSLO Status Operational t RSTM Operational Reset Figure 42. DAC RESET/PWDN Table 12. Timing Characteristics for Figure 42 SYMBOL DESCRIPTION MIN tRSLO PWDN/RESET pulse width low for power-down tRSTM PWDN/RESET high to begin operation MAX 2 UNIT tCLK 2 tCLK AVDD, AVSS, AND DVDD POWER SUPPLIES The DAC1282 has two power supplies: analog and digital. The analog supply (AVDD, AVSS) is 5 V and can either be single 5 V or dual (±2.5 V). The analog supply should be clean and free from noise and ripple. The DAC1282 regulates the output common-mode voltage to 0.1 V below the mid-point of the analog supply. Because the analog supply pins draw signal-dependent current and AVSS (pin 14) is internally shared with the reference input low, trace resistance between AVSS (pin 14) and the AVSS power supply should be minimized or degraded performance may result. Therefore, connect the external reference ground terminal close to the device AVSS terminal using a star connection. This configuration helps to minimize power-supply coupling to the reference input. DVDD is the digital supply used to power both the internal digital and the device I/O pins. The allowable range of DVDD is 1.65 V to 3.6 V. The power supplies can be sequenced on or off in any order, but the analog or digital inputs should never exceed AVDD or AVSS, or DVDD, respectively. In such an event, the internal ESD protection diodes may begin to conduct. The input current must always be limited as specified in the Absolute Maximum Ratings table. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 25 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com At power-on, when the latter of DVDD exceeds approximately 1.3 V, or the difference of AVDD – AVSS exceeds approximately 1.4 V, an internal power-on reset (POR) occurs. During POR, the device is held in a reset condition for a period of 216 fCLK periods as shown in Figure 43. During this time, the DAC1282 output is held at 0 V, differential. SPI communications are not possible during this time. After the reset time elapses, the default settings are loaded: 31.25 Hz, 28 mVRMS amplitude, and output switch off. SPI communications can then be started. AVDD - AVSS 1.4 V nom DVDD 1.3 V nom CLK 16 2 t CLK Status Reset Operational Figure 43. Power-On Sequence Power Consumption The power consumed by the DAC1282 depends on the analog gain. Table 13 shows the DAC power consumption. Table 13. Power Consumption (1) ANALOG GAIN POWER (mW) (1) 1/1 38 1/2 28 1/4 23 1/8 21 1/16 20 1/32 20 1/64 20 Typical power consumption with VREF = 5 V and VOUT = 0 V. Excludes pulse mode. Offset and Gain Error The DAC1282 features a low offset error ( ±7/Gain + 50 ppm FS typical) and low gain error (0.1 % typical). Offset and gain drift are also very low for the DAC1282. Drift is calculated using the box calculation method of Equation 4: Drift Calculation = (Max – Min)/Temperature Range (ppm/°C) Where: Max and Min are, respectively, the maximum and minimum offset and gain errors (in ppm) recorded over the specified temperature range of –40°C to +85°C. (4) Gain match is the gain error of Gain = 1/1 relative to all analog gains. Signal-to-Noise Ratio (SNR) The DAC1282 achieves excellent signal-to-noise ratio (SNR) performance. The SNR data are obtained using the DAC circuit of Figure 50 and data captured by the ADS1282. SNR is measured with a signal level of –0.5 dBFS and a 31.25-Hz test frequency, then taking the fast fourier transform (FFT) of 4096 data points from the ADS1282, using complementing gains. The noise power is calculated over the bandwidth of 413 Hz (1-ms sample period). The dc, fundamental, and harmonic bins are removed to calculate the SNR. The SNR measurement represents the combination of the ADS1282 SNR and the SNR of the DAC1282. 26 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com DC Noise DC noise data are obtained using the DAC circuit of Figure 50 with data captured by the ADS1282. The noise is measured in dc mode with the output voltage set to 0 V differential. The ADC gain is set to the complement of the DAC gain for each output range. The noise is the standard deviation of 4096-point ADC acquisition record (RMS noise, referred-to-output). Total Harmonic Distortion (THD) The DAC1282 achieves excellent THD performance. The THD data are obtained using the DAC circuit of Figure 50 and captured by the ADS1282. The ADC gain is set to the complement of the DAC gain for each output range. THD is measured with a –0.5-dBFS output signal level and a 31.25-Hz test frequency, then taking the FFT of the 4096-point ADC acquisition record. The ADC data points are increased to 16,384 for gains of 1/16, 1/32, and 1/64 for improved rendition of harmonics as a result of the higher noise floor. The THD measurement represents the combination of the ADS1282 THD and the DAC1282 THD. STEP RESPONSE The step response of the DAC depends on the mode. In pulse mode, the DAC disables the external analog filter formed by capacitors CAPP, CAPN. Disabling the analog filter in conjunction with the fast response pulse DAC results in noticeably faster rise time and shorter settling time. Note that additional filter components in the signal path may also affect the response time. Figure 44 shows the pulse mode step response after the SYNC pin transition. Figure 45 shows the pulse mode detail settling to 0.1% of final value after the SYNC pin transition. 2 0.5 (VOUTP − VOUTN) Pulse Mode Full scale step Settling to final value (%) 0.4 Amplitude (V) 1 VOUTP, VOUTN Pulse mode Full Scale Step 0 −1 −2 0 2 4 6 8 10 Time (µs) 0.2 0.1 0 −0.1 −0.2 −0.3 −0.4 SYNC pin transition −2 0.3 12 14 16 18 −0.5 −50 G000 Figure 44. Pulse Mode Step Response 0 50 SYNC pin transition 100 150 200 250 300 350 400 450 Time (µs) G000 Figure 45. Pulse Mode Step Response Detail Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 27 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com Figure 46 shows the step response time of the dc mode. The step response of sine and digital data mode have similar settling times. Note that additional filter components in the signal path may also affect the response time. 2 Amplitude (V) 1 VOUTP, VOUTN DC mode Full Scale Step 0 −1 SYNC pin transition −2 −50 0 50 100 150 200 250 300 350 400 450 Time (µs) G000 Figure 46. DC Mode Step Response FREQUENCY RESPONSE The DAC internal signal generator is capable of output signal frequencies from 0.489 Hz to 250 Hz. Frequencies outside of this range are also possible by driving the DAC directly with an external digital input (bitstream). However, the DAC low-pass filters the digital input and results in a sinx/x frequency response. The –3 dB signal bandwidth of the DAC filter is 8.2 kHz. Figure 47 illustrates the DAC1282 frequency response. Note that high-order noise-shaped digital inputs may limit the useable frequency range as a result of rising noise. OUTPUT FREQUENCY RESPONSE 0 CLK = 4.096MHz Excludes I/V Filter Rolloff Magnitude (dB) -10 -20 -30 -40 -50 -60 0 5 10 15 20 25 30 35 40 45 50 Output Frequency (kHz) Figure 47. DAC Frequency Response 28 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com SERIAL INTERFACE Configuration of the DAC is by an SPI-compatible serial interface consisting of four signals: CS, SCLK, DIN, and DOUT; or the interface can consist of three signals in which case CS may be tied low. Tying CS low permanently selects the device and DOUT remains a driven output. The interface is used to read and write registers and also is used to send a DAC reset command. Serial Communications DAC1282 communication occurs by clocking register data into the device (on DIN) and reading back register data (on DOUT). The SCLK input is used to clock data into and out of the device. Data are input on the serial clock (SCLK) rising edge and output on the SCLK falling edge. The communication protocol is half-duplex (that is, data are transmitted to and from the device one direction at a time). Communications to the device occur on 8-bit boundaries. If an unintentional SCLK transition should occur (such as is possible from a noise spike), the DAC1282 command decoder can be out-of-sync and the serial port may not respond properly. The serial port may reset in one of the following ways: 1. Take CS high to reset the interface 2. Hold SCLK inactive (low state) for 218 fCLK cycles to automatically reset the interface (see the SPI Timeout section) 3. Take RESET/PWDN low then back high to reset the device and the interface 4. Cycle the power supplies for a power-on reset (POR) Chip Select (CS) CS (chip select) selects the DAC1282 for communication. To select the device, pull CS low. CS must remain low for the duration of the command sequence. When CS is taken high, the serial interface is reset, input commands are ignored, and DOUT enters a high-impedance state. Serial Clock (SCLK) The serial clock (SCLK) is a Schmitt-triggered input used to clock data into and out of the DAC1282. SCLK can be idled high or low. If SCLK is idled low, the SPI timeout feature is active. If SCLK is idled high, the SPI timeout feature is disabled. Despite the built-in Schmitt-trigger, keep SCLK as clean as possible to prevent glitches from accidently shifting the data. Series-terminated printed circuit board (PCB) traces often help to reduce ringing and overshoot (series termination resistance is approximately 20 Ω to 50 Ω). If SCLK is held low for 218 fCLK periods, the serial interface is reset. The timeout feature can be used to automatically recover the SPI port in the event of a noise glitch. Avoid starting new commands after this time interval to prevent an unexpected serial port reset at the next command instant. Data Input (DIN) DIN is the data input pin used to send data to the DAC. The DAC1282 latches DIN input data on the rising edge of SCLK. Data Output (DOUT) DOUT is the data output pin used to read register data out of the DAC. The data are shifted out on the falling edge of SCLK. DOUT enters a 3-state when CS is high. SPI TIMEOUT The DAC has an SPI timeout feature that can be used to recover the SPI port if a possible noise pulse should occur. The noise pulse may lead to a false SCLK detection that can render the DAC serial port unresponsive. The port is recovered by taking CS high but, in applications where CS is tied low, holding SCLK low for 218 CLK cycles resets the SPI port automatically. When SCLK is low, the SPI port resets on every 218 CLK cycle interval. Holding SCLK high disables the automatic SPI reset. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 29 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com COMMANDS The commands summarized in Table 14 control and configure the DAC1282. The register read and register write commands are two-byte command arguments plus additional data bytes while the reset command is a one-byte command. The DAC1282 serial port chip select (CS) can be taken high or held low between commands but must remain low for the entire command operation. Table 14. Command Definitions (1) COMMAND TYPE DESCRIPTION FIRST OPCODE BYTE SECOND OPCODE BYTE RREG Register Read nnnn register(s) at address rrrr (1) 0010 rrrr 0000 nnnn WREG Register Write nnnn register(s) at address rrrr 0100 rrrr 0000 nnnn RESET Control Reset the device 0000 011x (06 or 07h) rrrr = Starting read or write register address, nnnn= number of registers to read or write minus 1. RREG: Read from Registers Description: These two opcode bytes read register data. The register read operation is a two-byte opcode input followed by one or more bytes of register data as the output. The first byte of the command is the opcode and the register address combined. The second byte of the command specifies the number of registers to read (minus 1) in a block. Register data are output following the command input. Note that for multiple register read operations, the register address pointer does not wrap when the last register is exceeded. First opcode byte: 0010 rrrr, where rrrr is the starting address register address to be read. Second opcode byte: 0000 nnnn, where nnnn is the number of registers to read – 1. Following bytes: Register data output in MSB-first format. The 16th SCLK falling edge of the opcode clocks out the MSB of the register data. CS (1) 1 9 17 25 SCLK DIN DOUT OPCODE 1 Don’t Care OPCODE 2 REG DATA 1 REG DATA 2 (1) CS may be tied low. Figure 48. RREG Command Example: Read Two Registers Starting from Register 00h (OPCODE 1 = 0010 0000, OPCODE 2 = 0000 0001) 30 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com WREG: Write to Registers Description: These two opcode bytes write register data. The register write operation is a two-byte opcode followed by one or more bytes of register data. The first byte of the command is the write opcode and the register address combined. The second byte of the command specifies the number of registers to write (minus 1) in a single sequence. The following bytes are the register data bytes. Note that for multiple register write operations, the register address pointer does not wrap when the last register is exceeded. First opcode byte: 0010 rrrr, where rrrr is the starting address register address to be written. Second opcode byte: 0000 nnnn, where nnnn is the number of registers to write – 1. Following bytes: Register data input in MSB-first format. CS (1) 1 9 17 25 SCLK DIN DOUT OPCODE 1 OPCODE 2 REG DATA 1 REG DATA 2 Don’t Care (1) CS may be tied low. Figure 49. WREG Command Example: Write Two Registers Starting from Register 00h (OPCODE 1 = 0100 0000, OPCODE 2 = 0000 0001) RESET: Device Reset Description: This command resets the DAC. The registers are set to power-on default the value; see the RESET/PWDN section. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 31 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com REGISTER MAP DAC1282 operation is controlled through a set of 8-bit registers. Collectively, the registers contain all the information needed to configure the DAC, such as output frequency and amplitude, output pulse levels, etc. Table 15 shows the register map. The default state of the device at power-up, after the RESET pin is taken high or after a RESET command is as follows: Sine mode, frequency = 31.25 Hz, –36-dB output range, 0-dB digital attenuation Switch state: open Table 15. Register Map ADDRESS REGISTER DEFAULT BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 0 GANMOD xxx11000 ID2 ID1 ID0 GAIN2 GAIN1 GAIN0 MODE1 MODE0 1 SING 00000000 SINEG7 SINEG6 SINEG5 SINEG4 SINEG3 SINEG2 SINEG1 SINEG0 2 SWM 00000000 FREQ SW2 SW1 SW0 M3 M2 M1 M0 3 N 00000111 N7 N6 N5 N4 N3 N2 N1 N0 4 DCG0 00000000 DCG7 DCG6 DCG5 DCG4 DCG3 DCG2 DCG1 DCG0 5 DCG1 00000000 DCG15 DCG14 DCG13 DCG12 DCG11 DCG10 DCG9 DCG8 6 DCG2 00000000 DCG23 DCG22 DCG21 DCG20 DCG19 DCG18 DCG17 DCG16 7 PULSA 00000000 0 0 0 PULSA4 PULSA3 PULSA2 PULSA1 PULSA0 8 PULSB 00000000 0 0 0 PULSB4 PULSB3 PULSB2 PULSB1 PULSB0 Table 16. GANMOD: Range and Mode Register 0 (Address = 0h) 7 6 5 4 3 2 1 0 ID2 ID1 ID0 GAIN2 GAIN1 GAIN0 MODE1 MODE0 Bits[7:5] ID[2:0]: Factory-programmed identification bits (read-only) These bits may change at any time without notification. Bits[4:2] GAIN[2:0]: Analog gain (output range) These bits set the analog gain in the sine, dc, and bitstream modes. The output amplitude is the combination of the selected range and the digital gain. Sine mode digital gain is programmed by the SINEG register; dc mode digital gain are the DCG0, DCG1, and DCG2 registers. Pulse mode levels are exclusively controlled by the PULSA and PULSB registers. GAIN[2:0] Bits[1:0] OUTPUT (dB) OUTPUT RANGE (V) (1) 000 0 ±2.5 001 –6 ±1.25 010 –12 ±0.625 011 –18 ±0.312 100 –24 ±0.156 101 –30 ±0.078 110 (default) –36 ±0.039 MODE[1:0]: Mode control bits The mode bits set the mode of operation. When the mode bits are changed, the internal signal generator block is reset. 00 01 10 11 (1) 32 = Sine mode (default) = DC mode = Digital data mode = Pulse mode (Peak-to-peak) full-scale output range, VREF = 5 V. Digital gain = 0 dB. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com SINEG: Sine Mode Digital Gain Register (Address = 01h) 7 6 5 4 3 2 1 0 SINEG7 SINEG6 SINEG5 SINEG4 SINEG3 SINEG2 SINEG1 SINEG0 Bits[7:0] SINEG[7:0]: Sine mode digital gain This register byte sets the sine mode digital gain from 0 dB to –119.5 dB and to full mute, in 0.5-dB steps. The sine mode digital gain can be expressed as: –DGAIN[7:0]/2 (dB) and are listed in Table 17. Table 17. Sine Mode Digital Gain SINEG[7:0] REGISTER SINE MODE DIGITAL GAIN (dB) 0000 0000 (default) 0.0 0000 0001 –0.5 0000 0010 –1.0 … … 1110 1111 –119.5 1111 0000 Full mute … Full mute 1111 1111 Full mute SWM: Switch, Output Frequency 'M', and Range Bit Register (Address = 02h) 7 6 5 4 3 2 1 0 FREQ SW2 SW1 SW0 M3 M2 M1 M0 Bit 7 FREQ: Frequency This bit sets the sine mode output frequency range; see Equation 1. Bits[6:4] SW[2:0]: Switch control bits These bits control the switch settings when the SW/TD input is high. When SW/TD is low, the register is ignored and the switch is forced open. In digital input mode, the switch is controlled only by the register. Bits[3:0] SW[2:0] SWITCH DESCRIPTION TERMINAL CONNECTIONS 000 Open (default) All switches open 001 Differential SWINP to SWOUTP and SWINN to SWOUTN 010 Differential reverse SWINP to SWOUTN and SWINN to SWOUTP 011 Common-mode positive SWINP to SWOUTP and SWINP to SWOUTN 100 Common-mode negative SWINN to SWOUTP and SWINN to SWOUTN 101 Single-ended positive SWINP to SWOUTP only 110 Single-ended negative SWINN to SWOUTN only 111 Short SWOUTP to SWOUTN M[3:0]: Sine mode frequency, M bits These bits control the sine-mode output frequency. The output frequency is given in Equation 1. Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 33 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com N: Sine Frequency N Register (Address = 03h) 7 6 5 4 3 2 1 0 N7 N6 N5 N4 N3 N2 N1 N0 Bits[7:0] N[7:0]: N register These bits control the output frequency; see Equation 1. DCG0: DC Mode Digital Gain Byte 0, Least Significant Byte (Address = 04h) 7 6 5 4 3 2 1 0 DCG7 DCG6 DCG5 DCG4 DCG3 DCG2 DCG1 DCG0 7 6 5 4 3 2 1 0 DCG15 DCG14 DCG13 DCG12 DCG11 DCG10 DCG9 DCG8 DCG1: DC Mode Digital Gain Byte 1, Mid Byte (Address = 05h) DCG2: DC Mode Digital Gain Byte 2, Most Significant Byte (Address = 06h) 7 6 5 4 3 2 1 0 DCG23 DCG22 DCG21 DCG20 DCG19 DCG18 DCG17 DCG16 Bits[7:0] DCG[23:0]: DC mode digital gain setting The DCG0, DCG1, and DCG2 register bytes set the digital gain in dc mode; see Table 5. PULSA: Pulse Level A Byte (Address = 07h) 7 6 5 4 3 2 1 0 0 0 0 PULSA4 PULSA3 PULSA2 PULSA1 PULSA0 Bits[7:5] Reserved Always write '0'. Bits[4:0] PULSA[4:0]: Pulse level A bits These bits create pulse level A. (Selected output when SYNC is low.) The PULSA and PULSB registers set two independent levels that can be used to provide pulse output. The SYNC pin selects either level PULSA or level PULSB as the DAC output. The pulse amplitude resolution is programmable in discrete steps, as shown in Table 6. Note that the pulse level value is independent of the RANGE[2:0] setting. PULSB: Pulse Level B Byte (Address = 08h) 7 6 5 4 3 2 1 0 0 0 0 PULSB4 PULSB3 PULSB2 PULSB1 PULSB0 Bits[7:5] Reserved Always write '0'. Bits[4:0] PULSB[4:0]: Pulse level B bits These bits create pulse level B. The PULSA and PULSB registers set two independent levels that can be used to provide pulse output. The SYNC pin selects either level PULSA or level PULSB as the DAC output. The pulse amplitude resolution is programmable in discrete steps; see Table 6. Note that the pulse level value is independent of the RANGE[2:0] setting. 34 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com APPLICATION INFORMATION BASIC CONNECTION Figure 50 shows the basic DAC1282 connection. Bipolar analog supplies are shown (±2.5 V). Single-supply operation is also possible with AVDD = 5 V and AVSS = GND. The digital supply range is 1.65 V to 3.6 V. A low-noise, low-drift reference is recommended for best performance, such as the REF5050 (+5 V) and REF5045 (+4.5 V). Best signal-to-noise ratio is achieved with a 5-V reference, although a 4.5-V reference (REF5045) can be used with 1-dB loss in SNR. The 4.5-V reference can be operated from a 5-V supply. AVSS (pin 14) is the key reference ground point and should be connected to the reference ground terminal using a star connection. C1 and C2 are the required 1-nF output filter capacitors. The capacitors should be of the low volt-coefficient type (such as a COG ceramic or similar) and placed close to the device pins. Output resistors, R1 and R2, decouple the DAC to ensure best performnace when driving capacitive loads. The output is shown routed to the signal switch, providing a second, switched DAC output. +V REF5050 REF5045 1 µF NR 100 µF 4.7 µF -2.5 V +3.3 V 1 µF 1 µF 50 Ω +2.5 V 0.1 µF 1 µF 4.096 MHz DVDD CLK Controller AVSS (23) AVDD (24) AVDD (13) AVSS (14) VREF CAPP CS C1 1 nF C0G 50 Ω SCLK R1 50 Ω VOUTP DIN DAC1282 DOUT 50 Ω Output VOUTN SYNC C2 1 nF C0G 50 Ω SW/TD R2 50 Ω CAPN RESET/PWDN DGND SWOUTN SWOUTP SWINP SWINN Switched Output Figure 50. Basic Connection Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 35 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com SINGLE-CHANNEL SEISMIC SYSTEM Figure 51 illustrates a single-channel data acquisition concept for seismic. The DAC1282 is used to test both the ADC and geophone. The DAC1282 connects directly to channel 1 of the ADC. Tests of the ADC include THD, pulse, input noise, common-mode, etc. The DAC output and ADC sample timing are controlled by the SYNC input pins. The geophone connects to channel 2 of the ADC through input protection and optional filter networks. The DAC connects to the geophone using the integrated signal switch. Series resistors isolate the geophone from the DAC output. Geophone test capabilities include impulse, THD, leakage, and common-mode. VOUTP DAC1282 Switch Out Geophone Protection Inp1 ADS1282 VOUTN Switch In Inp2 Filtering Figure 51. Single-Channel Seismic System 36 Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 DAC1282 SBAS490 – DECEMBER 2011 www.ti.com FOUR-CHANNEL SEISMIC SYSTEM Figure 52 illustrates a four-channel system. The switched DAC1282 output is routed to the ADC inputs. The signal from the DAC switch is used to perform sensor impulse testing by opening the switch while digitizing the response. DAC1282 Switched Output ADS1282 Geophone Protection + Filtering Geophone Protection + Filtering Geophone Protection + Filtering Geophone Protection + Filtering ADS1282 ADS1282 ADS1282 Figure 52. Four-Channel Seismic System Submit Documentation Feedback Copyright © 2011, Texas Instruments Incorporated Product Folder Link(s): DAC1282 37 PACKAGE OPTION ADDENDUM www.ti.com 23-Dec-2011 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan (2) Lead/ Ball Finish MSL Peak Temp (3) DAC1282IPW ACTIVE TSSOP PW 24 60 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR DAC1282IPWR ACTIVE TSSOP PW 24 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR Samples (Requires Login) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. 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Addendum-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device DAC1282IPWR Package Package Pins Type Drawing TSSOP PW 24 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2000 330.0 16.4 Pack Materials-Page 1 6.95 B0 (mm) K0 (mm) P1 (mm) 8.3 1.6 8.0 W Pin1 (mm) Quadrant 16.0 Q1 PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) DAC1282IPWR TSSOP PW 24 2000 367.0 367.0 38.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46C and to discontinue any product or service per JESD48B. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 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