19-1688; Rev 0; 5/00 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference Features ♦ 4-Channel Single-Ended or 2-Channel Pseudo-Differential Inputs The 4-wire serial interface connects directly to SPI™/QSPI™/MICROWIRE™ devices without external logic. A serial strobe output allows direct connection to TMS320-family digital signal processors. The MAX1282/ MAX1283 use an external serial-interface clock to perform successive-approximation analog-to-digital conversions. The devices feature an internal +2.5V reference and a reference-buffer amplifier with a ±1.5% voltage-adjustment range. An external reference with a 1V to VDD range may also be used. ♦ 400kHz Sampling Rate (MAX1282) The MAX1282/MAX1283 provide a hardwired SHDN pin and four software-selectable power modes (normal operation, reduced power (REDP), fast power-down (FASTPD), and full power-down (FULLPD)). These devices can be programmed to automatically shut down at the end of a conversion or to operate with reduced power. When using the power-down modes, accessing the serial interface automatically powers up the devices, and the quick turnon time allows them to be shut down between all conversions. ♦ 16-Pin TSSOP Package The MAX1282/MAX1283 are available in 16-pin TSSOP packages. ♦ Internal Multiplexer and Track/Hold ♦ Single-Supply Operation +4.5V to +5.5V (MAX1282) +2.7V to +3.6V (MAX1283) ♦ Internal +2.5V Reference ♦ Low Power: 2.5mA (400ksps) 1.3mA (REDP) 0.9mA (FASTPD) 2µA (FULLPD) ♦ SPI/QSPI/MICROWIRE/TMS320-Compatible 4-Wire Serial Interface ♦ Software-Configurable Unipolar or Bipolar Inputs Ordering Information TEMP. RANGE PART PINPACKAGE INL (LSB) MAX1282BCUE 0°C to +70°C 16 TSSOP ±1 MAX1282BEUE -40°C to +85°C 16 TSSOP ±1 MAX1283BCUE 0°C to +70°C 16 TSSOP ±1 MAX1283BEUE -40°C to +85°C 16 TSSOP ±1 Pin Configuration Applications Portable Data Logging Data Acquisition TOP VIEW Medical Instruments VDD1 1 16 VDD2 Battery-Powered Instruments CH0 2 15 SCLK Pen Digitizers CH1 3 Process Control CH2 4 CH3 5 Typical Operating Circuit appears at end of data sheet. 14 CS MAX1282/ MAX1283 13 DIN 12 SSTRB COM 6 11 DOUT SHDN 7 10 GND REF 8 9 REFADJ TSSOP SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp. ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX1282/MAX1283 General Description The MAX1282/MAX1283 12-bit analog-to-digital converters (ADCs) combine a 4-channel analog-input multiplexer, high-bandwidth track/hold (T/H), and serial interface with high conversion speed and low power consumption. The MAX1282 operates from a single +4.5V to +5.5V supply; the MAX1283 operates from a single +2.7V to +3.6V supply. Both devices’ analog inputs are software configurable for unipolar/bipolar and single-ended/pseudo-differential operation. MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference ABSOLUTE MAXIMUM RATINGS VDD_ to GND ........................................................... -0.3V to +6V VDD1 to VDD2 ....................................................... -0.3V to +0.3V CH0–CH3, COM to GND .......................... -0.3V to (VDD_ +0.3V) REF, REFADJ to GND ................................ -0.3V to VDD_ +0.3V) Digital Inputs to GND .............................................. -0.3V to +6V Digital Outputs to GND............................. -0.3V to (VDD_ +0.3V) Digital Output Sink Current .................................................25mA Continuous Power Dissipation (TA = +70°C) 16-Pin TSSOP (derate 6.7mW/°C above +70°C) ........ 535mW Operating Temperature Ranges MAX1282BCUE/MAX1283BCUE ....................... 0°C to +70°C MAX1282BEUE/MAX1283BEUE ..................... -40°C to +85°C Storage Temperature Range ............................ -60°C to +150°C Lead Temperature (soldering, 10s) ................................ +300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS—MAX1282 (VDD1 = VDD2 = +4.5V to +5.5V, COM = GND, fOSC = 6.4MHz, 50% duty cycle, 16 clocks/conversion cycle (400ksps), external +2.5V at REF, REFADJ = VDD1, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC ACCURACY (Note 1) 12 Resolution Bits ±1.0 LSB ±1.0 LSB Offset Error ±6.0 LSB Gain Error (Note 3) ±6.0 LSB Relative Accuracy (Note 2) INL Differential Nonlinearity DNL No missing codes over temperature Gain-Error Temperature Coefficient ±1.6 ppm/°C Channel-to-Channel Offset-Error Matching ±0.2 LSB DYNAMIC SPECIFICATIONS (100kHz sine-wave input, 2.5Vp-p, 400ksps, 6.4MHz clock, bipolar input mode) Signal-to-Noise plus Distortion Ratio SINAD Total Harmonic Distortion THD Spurious-Free Dynamic Range SFDR Up to the 5th harmonic 70 dB -81 dB 80 dB fIN1 = 99kHz, fIN2 =102kHz 76 dB Channel-to-Channel Crosstalk (Note 4) 200kHz, VIN = 2.5Vp-p -78 dB Full-Power Bandwidth -3dB point 6 MHz Full-Linear Bandwidth SINAD > 68dB 350 kHz Intermodulation Distortion IMD CONVERSION RATE Conversion Time (Note 5) tCONV Track/Hold Acquisition Time tACQ 2.5 µs 400 ns Aperture Delay 10 ns Aperture Jitter <50 ps Serial Clock Frequency Duty Cycle 2 fSCLK 0.5 6.4 MHz 40 60 % _______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference (VDD1 = VDD2 = +4.5V to +5.5V, COM = GND, fOSC = 6.4MHz, 50% duty cycle, 16 clocks/conversion cycle (400ksps), external +2.5V at REF, REFADJ = VDD1, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ANALOG INPUTS (CH3–CH0, COM) Input Voltage Range, SingleEnded and Differential (Note 6) VREF Unipolar, VCOM = 0 VCH_ Bipolar, VCOM or VCH_ = VREF/2, referenced to COM or CH_ ±VREF/2 On/off leakage current, VCOM, VCH_ = 0 or VDD1 Multiplexer Leakage Current ±0.001 Input Capacitance ±1 18 V µA pF INTERNAL REFERENCE REF Output Voltage VREF TA = +25°C 2.480 REF Short-Circuit Current REF Output Temperature Coefficient TC VREF 2.500 2.520 V 15 mA ±15 ppm/°C 2.0 mV/mA Capacitive Bypass at REF 4.7 10 µF Capacitive Bypass at REFADJ 0.01 10 µF Load Regulation (Note 7) 0.05 0 to 1mA output load REFADJ Output Voltage REFADJ Input Range For small adjustments, from 1.22V REFADJ Buffer Disable Threshold To power down the internal reference 1.22 V ±100 mV 1.4 VDD1 - 1.0 +2.05 Buffer Voltage Gain V V/V EXTERNAL REFERENCE (reference buffer disabled, reference applied to REF) REF Input Voltage Range (Note 8) 1.0 VREF = 2.500V, fSCLK = fMAX REF Input Current VDD1 + 50mV 200 VREF = 2.500V, fSCLK = 0 350 320 In full power-down mode, fSCLK = 0 V µA 5 DIGITAL INPUTS (DIN, SCLK, CS, SHDN) Input High Voltage VINH Input Low Voltage 3.0 V VINL Input Hysteresis VHYST Input Leakage IIN Input Capacitance CIN 0.8 V ±1 µA 0.2 VIN = 0 or VDD2 V 15 pF DIGITAL OUTPUTS (DOUT, SSTRB) Output Voltage Low VOL ISINK = 5mA Output Voltage High VOH ISOURCE = 1mA Three-State Leakage Current Three-State Output Capacitance IL CS = VDD2 COUT CS = VDD2 0.4 V ±10 µA 4 V 15 pF _______________________________________________________________________________________ 3 MAX1282/MAX1283 ELECTRICAL CHARACTERISTICS—MAX1282 (continued) MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference ELECTRICAL CHARACTERISTICS—MAX1282 (continued) (VDD1 = VDD2 = +4.5V to +5.5V, COM = GND, fOSC = 6.4MHz, 50% duty cycle, 16 clocks/conversion cycle (400ksps), external +2.5V at REF, REFADJ = VDD1, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 5.5 V POWER SUPPLY Positive Supply Voltage (Note 9) Supply Current VDD1, VDD2 IVDD1+ IVDD2 4.5 VDD1 = VDD2 = 5.5V Normal operating mode (Note 10) 2.5 4.0 Reduced-power mode (Note 11) 1.3 2.0 Fast power-down mode (Note 11) 0.9 1.5 Full power-down mode (Note 11) Power-Supply Rejection PSR VDD1 = VDD2 = 5V ±10%, midscale input mA 2.0 10 µA ±0.5 ±2.0 mV ELECTRICAL CHARACTERISTICS—MAX1283 (VDD1 = VDD2 = +2.7V to +3.6V, COM = GND, fOSC = 4.8MHz, 50% duty cycle, 16 clocks/conversion cycle (300ksps), external +2.5V at REF, REFADJ = VDD1, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ±1.0 LSB ±1.0 LSB Offset Error ±6.0 LSB Gain Error (Note 3) ±6.0 LSB DC ACCURACY (Note 1) 12 Resolution Relative Accuracy (Note 2) INL Differential Nonlinearity DNL Bits No missing codes over temperature Gain-Error Temperature Coefficient ±1.6 ppm/°C Channel-to-Channel Offset-Error Matching ±0.2 LSB DYNAMIC SPECIFICATIONS (100kHz sine-wave input, 2.5Vp-p, 400ksps, 6.4MHz clock, bipolar input mode) Signal-to-Noise plus Distortion Ratio 70 dB -70 dB 72 dB fIN1 = 73kHz, fIN2 = 77kHz 76 dB Channel-to-Channel Crosstalk (Note 4) f = 150kHz, VIN = 2.5Vp-p -78 dB Full-Power Bandwidth -3dB point 3 MHz Full-Linear Bandwidth SINAD > 68dB 250 kHz SINAD Total Harmonic Distortion THD Spurious-Free Dynamic Range SFDR Intermodulation Distortion 4 IMD Up to the 5th harmonic _______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference (VDD1 = VDD2 = +2.7V to +3.6V, COM = GND, fOSC = 4.8MHz, 50% duty cycle, 16 clocks/conversion cycle (300ksps), external +2.5V at REF, REFADJ = VDD1, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CONVERSION RATE Conversion Time (Note 5) tCONV Normal operating mode Track/Hold Acquisition Time tACQ Normal operating mode 3.3 µs 625 Aperture Delay 10 Aperture Jitter <50 Serial Clock Frequency fSCLK Normal operating mode Duty Cycle ns ns ps 0.5 4.8 MHz 40 60 % ANALOG INPUTS (CH3–CH0, COM) Input Voltage Range, Single Ended and Differential (Note 6) VREF Unipolar, VCOM = 0 VCH_ Multiplexer Leakage Current Bipolar, VCOM or VCH_ = VREF/2, referenced to COM or CH_ ±VREF/2 On/off leakage current, VCH_ = 0 or VDD1 ±0.001 Input Capacitance ±1 18 V µA pF INTERNAL REFERENCE REF Output Voltage VREF TA = +25°C 2.480 REF Short-Circuit Current REF Output Temperature Coefficient TC VREF Load Regulation (Note 7) 4.7 Capacitive Bypass at REFADJ 0.01 REFADJ Output Voltage For small adjustments, from 1.22V REFADJ Buffer Disable Threshold To power down the internal reference 2.520 mA ±15 ppm/°C 2.0 mV/mA 10 µF 10 µF 1.22 V ±100 mV 1.4 VDD1 - 1.0 2.05 Buffer Voltage Gain EXTERNAL REFERENCE (reference buffer disabled, reference applied to REF) Buffer Voltage Gain REF Input Voltage Range (Note 8) V/V VDD1 + 50mV 200 V 350 320 VREF = 2.500V, fSCLK = 0 V V/V 2.05 1.0 VREF = 2.500V, fSCLK = fMAX REF Input Current V 15 0.1 0 to 0.75mA output load Capacitive Bypass at REF REFADJ Input Range 2.500 µA 5 In full power-down mode, fSCLK = 0 DIGITAL INPUTS (DIN, SCLK, CS, SHDN) Input High Voltage VINH Input Low Voltage VINL Input Hysteresis 2.0 0.2 VHYST Input Leakage IIN Input Capacitance CIN V 0.8 V ±1 VIN = 0 or VDD2 15 V µA pF _______________________________________________________________________________________ 5 MAX1282/MAX1283 ELECTRICAL CHARACTERISTICS—MAX1283 (continued) MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference ELECTRICAL CHARACTERISTICS—MAX1283 (continued) (VDD1 = VDD2 = +2.7V to +3.6V, COM = GND, fOSC = 4.8MHz, 50% duty cycle, 16 clocks/conversion cycle (300ksps), external +2.5V at REF, REFADJ = VDD1, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DIGITAL OUTPUTS (DOUT, SSTRB) Output Voltage Low VOL ISINK = 5mA Output Voltage High VOH ISOURCE = 0.5mA Three-State Leakage Current Three-State Output Capacitance IL CS = VDD2 COUT CS = VDD2 0.4 VDD2 - 0.5V V V ±10 15 µA pF POWER SUPPLY Positive Supply Voltage (Note 9) Supply Current VDD1, VDD2 IVDD1 + IVDD2 2.7 VDD1 = VDD2 = 3.6V Normal operating mode (Note 10) 2.5 3.5 Reduced-power mode (Note 11) 1.3 2.0 Fast power-down mode (Note 11) 0.9 1.5 Full power-down mode (Note 11) Power-Supply Rejection PSR 3.6 VDD1 = VDD2 = 2.7V to 3.6V, midscale input V mA 2.0 10 µA ±0.5 ±2.0 mV TYP MAX UNITS TIMING CHARACTERISTICS—MAX1282 (Figures 1, 2, 5, 6; VDD1 = VDD2 = +4.5V to +5.5V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN SCLK Period tCP 156 ns SCLK Pulse Width High tCH 62 ns SCLK Pulse Width Low tCL 62 ns DIN to SCLK Setup tDS 35 ns DIN to SCLK Hold tDH 0 ns CS Fall to SCLK Rise Setup tCSS 35 ns SCLK Rise to CS Rise Hold tCSH 0 ns SCLK Rise to CS Fall Ignore tCSO 35 ns CS Rise to SCLK Rise Ignore tCS1 35 ns SCLK Rise to DOUT Hold tDOH CLOAD = 20pF 10 20 SCLK Rise to SSTRB Hold tSTH CLOAD = 20pF 10 20 SCLK Rise to DOUT Valid tDOV CLOAD = 20pF SCLK Rise to SSTRB Valid tSTV CLOAD = 20pF CS Rise to DOUT Disable tDOD CLOAD = 20pF 10 CS Rise to SSTRB Disable tSTD CLOAD = 20pF 10 CS Fall to DOUT Enable tDOE CS Fall to SSTRB Enable tSTE CS Pulse Width High tCSW 6 ns ns 80 ns 80 ns 65 ns 65 ns CLOAD = 20pF 65 ns CLOAD = 20pF 65 ns 100 _______________________________________________________________________________________ ns 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference (Figures 1, 2, 5, 6; VDD1 = VDD2 = +2.7V to +3.6V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SCLK Period tCP 208 ns SCLK Pulse Width High tCH 83 ns SCLK Pulse Width Low tCL 83 ns DIN to SCLK Setup tDS 45 ns DIN to SCLK Hold tDH 0 ns CS Fall to SCLK Rise Setup tCSS 45 ns SCLK Rise to CS Rise Hold tCSH 0 ns SCLK Rise to CS Fall Ignore tCSO 45 ns CS Rise to SCLK Rise Ignore tCS1 45 ns SCLK Rise to DOUT Hold tDOH CLOAD = 20pF 13 20 SCLK Rise to SSTRB Hold tSTH CLOAD = 20pF 13 20 SCLK Rise to DOUT Valid tDOV CLOAD = 20pF SCLK Rise to SSTRB Valid tSTV CLOAD = 20pF CS Rise to DOUT Disable tDOD CLOAD = 20pF 13 CS Rise to SSTRB Disable tSTD CLOAD = 20pF 13 CS Fall to DOUT Enable tDOE CS Fall to SSTRB Enable tSTE CS Pulse Width High tCSW ns ns 100 ns 100 ns 85 ns 85 ns CLOAD = 20pF 85 ns CLOAD = 20pF 85 ns 100 ns Note 1: Tested at VDD1 = VDD2 = VDD(MIN), COM = GND, unipolar single-ended input mode. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range has been calibrated. Note 3: Offset nulled. Note 4: Ground the “on” channel; sine wave is applied to all “off” channels. Note 5: Conversion time is defined as the number of clock cycles multiplied by the clock period; clock has 50% duty cycle. Note 6: The common-mode range for the analog inputs (CH3–CH0 and COM) is from GND to VDD1. Note 7: External load should not change during conversion for specified accuracy. Note 8: ADC performance is limited by the converter’s noise floor, typically 300µVp-p. An external reference below 2.5V compromises the performance of the ADC. Note 9: Electrical characteristics are guaranteed from VDD1(MIN) = VDD2(MIN) to VDD1(MAX) = VDD2(MIN). For operations beyond this range, see Typical Operating Characteristics. For guaranteed specifications beyond the limits, contact the factory. Note 10: AIN = midscale, unipolar mode. MAX1282 tested with 20pF on DOUT, 20pF on SSTRB, and fSCLK = 6.4MHz, 0 to 5V. MAX1283 tested with same loads, fSCLK = 4.8MHz, 0 to 3V. Note 11: SCLK = DIN = GND, CS = VDD1. _______________________________________________________________________________________ 7 MAX1282/MAX1283 TIMING CHARACTERISTICS—MAX1283 Typical Operating Characteristics (MAX1282: VDD1 = VDD2 = 5.0V, fSCLK = 6.4MHz; MAX1283: VDD1 = VDD2 = 3.0V, fSCLK = 4.8MHz; CLOAD = 20pF, 4.7µF capacitor at REF, 0.01µF capacitor at REFADJ, TA = +25°C, unless otherwise noted.) INTEGRAL NONLINEARITY vs. DIGITAL OUTPUT CODE SUPPLY CURRENT vs. SUPPLY VOLTAGE (CONVERTING) DIFFERENTIAL NONLINEARITY vs. DIGITAL OUTPUT CODE 0.3 0.2 0.1 DNL (LSB) 0 -0.1 0.1 0 -0.1 -0.2 -0.2 -0.4 -0.4 -0.5 0 500 1000 1500 2000 2500 3000 3500 4000 4500 1.5 0 2.5 500 1000 1500 2000 2500 3000 3500 4000 4500 3.0 3.5 4.0 4.5 5.0 5.5 DIGITAL OUTPUT CODE DIGITAL OUTPUT CODE SUPPLY VOLTAGE (V) SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. SUPPLY VOLTAGE (STATIC) SUPPLY CURRENT vs. TEMPERATURE (STATIC) 2.6 2.4 MAX1283 2.2 1.5 REDP (PD1 = 1, PD0 = 0) 1.0 FASTDP (PD1 = 0, PD0 = 1) MAX1282 (PD1 = 1, PD0 = 1) 2.0 SUPPLY CURRENT (mA) MAX1282 2.8 NORMAL OPERATION (PD1 = PD0 = 1) 2.0 SUPPLY CURRENT (mA) 3.0 2.5 MAX1282/3-05 2.5 MAX1282/3-04 3.2 SUPPLY CURRENT (mA) 2.5 2.0 -0.3 -0.3 3.0 MAX1282/3-06 INL (LSB) 0.2 MAX1282/3-03 0.4 SUPPLY CURRENT (mA) 0.3 3.5 MAX1280/1-02 0.5 MAX1280/1-01 0.4 MAX1283 (PD1 = 1, PD0 = 1) 1.5 MAX1282 (PD1 = 1, PD0 = 0) MAX1283 (PD1 = 1, PD0 = 0) 1.0 0.5 0.5 0 0 MAX1282 (PD1 = 0, PD0 = 1) MAX1283 (PD1 = 0, PD0 = 1) 2.0 0 20 40 60 80 3.0 3.5 4.0 4.5 5.0 5.5 0 20 40 60 SHUTDOWN CURRENT vs. SUPPLY VOLTAGE SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE REFERENCE VOLTAGE vs. SUPPLY VOLTAGE (PD1 = PD0 = 0) SUPPLY CURRENT (µA) 3 2 1 MAX1282 2.0 1.5 MAX1283 1.0 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 5.5 5.0 5.5 2.5005 2.5003 2.5001 2.4999 2.4995 0 3.5 100 2.4997 0.5 0 80 MAX1282/3-09 2.5 MAX1282/3-07 4 3.0 -20 TEMPERATURE (°C) (PD1 = PD0 = 0) 2.5 -40 SUPPLY VOLTAGE (V) 5 8 2.5 100 TEMPERATURE (°C) MAX1282/3-08 -20 REFERENCE VOLTAGE (V) -40 SUPPLY CURRENT (µA) MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference REFERENCE VOLTAGE vs. TEMPERATURE OFFSET ERROR vs. SUPPLY VOLTAGE MAX1283 2.4996 2.4994 0 1.0 OFFSET ERROR (LSB) 2.4998 0.5 0 -0.5 2.4992 -1.0 2.4990 -1.5 0 20 40 60 80 2.5 100 3.0 3.5 4.0 4.5 5.0 -1.0 -1.5 -2.5 5.5 -40 -15 SUPPLY VOLTAGE (V) TEMPERATURE (°C) 0.6 60 85 0.5 0 GAIN ERROR (LSB) 0.4 0.2 0 -0.2 MAX1282/3-14 0.8 35 GAIN ERROR vs. TEMPERATURE GAIN ERROR vs. SUPPLY VOLTAGE 1.0 10 TEMPERATURE (°C) MAX1282/3-13 -20 GAIN ERROR (LSB) -40 -0.5 -2.0 -2.0 2.4988 MAX1282/3-12 1.5 OFFSET ERROR (LSB) MAX1282 OFFSET ERROR vs. TEMPERATURE 0.5 MAX1282/3-11 2.5000 REFERENCE VOLTAGE (V) 2.0 MAX1282/3-10 2.5002 -0.5 -1.0 -0.4 -1.5 -0.6 -0.8 -2.0 -1.0 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 5.5 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 9 MAX1282/MAX1283 Typical Operating Characteristics (continued) (MAX1282: VDD1 = VDD2 = 5.0V, fSCLK = 6.4MHz; MAX1283: VDD1 = VDD2 = 3.0V, fSCLK = 4.8MHz; CLOAD = 20pF, 4.7µF capacitor at REF, 0.01µF capacitor at REFADJ, TA = +25°C, unless otherwise noted.) MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference Pin Description PIN NAME FUNCTION 1 VDD1 Positive Supply Voltage 2–5 CH0–CH3 Sampling Analog Inputs 6 COM Ground Reference for Analog Inputs. COM sets zero-code voltage in single-ended mode. Must be stable to ±0.5LSB. 7 SHDN Active-Low Shutdown Input. Pulling SHDN low shuts down the device, reducing supply current to 2µA (typ). 8 REF Reference-Buffer Output/ADC Reference Input. Reference voltage for analog-to-digital conversion. In internal reference mode, the reference buffer provides a 2.500V nominal output, externally adjustable at REFADJ. In external reference mode, disable the internal buffer by pulling REFADJ to VDD1. 9 REFADJ Input to the Reference-Buffer Amplifier. To disable the reference-buffer amplifier, connect REFADJ to VDD1. 10 GND Ground 11 DOUT Serial-Data Output. Data is clocked out at SCLK’s rising edge. High impedance when CS is high. 12 SSTRB Serial Strobe Output. SSTRB pulses high for one clock period before the MSB decision. High impedance when CS is high. 13 DIN Serial-Data Input. Data is clocked in at SCLK’s rising edge. 14 CS Active-Low Chip Select. Data will not be clocked into DIN unless CS is low. When CS is high, DOUT and SSTRB are high impedance. 15 SCLK Serial-Clock Input. Clocks data in and out of serial interface and sets the conversion speed. (Duty cycle must be 40% to 60%.) 16 VDD2 Positive Supply Voltage VDD2 VDD2 DOUT DOUT CLOAD 50pF 3k CLOAD 50pF GND GND a) High-Z to VOH and VOL to VOH b) High-Z to VOL and VOH to VOL Figure 1. Load Circuits for Enable Time 10 3k 3k DOUT DOUT CLOAD 70pF 3k GND a) VOH to High-Z Figure 2. Load Circuits for Disable Time ______________________________________________________________________________________ CLOAD 20pF GND b) VOL to High-Z 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference The MAX1282/MAX1283 ADCs use a successiveapproximation conversion technique and input T/H circuitry to convert an analog signal to a 12-bit digital output. A flexible serial interface provides easy interface to microprocessors (µPs). Figure 3 shows a functional diagram of the MAX1282/MAX1283. Pseudo-Differential Input The equivalent circuit of Figure 4 shows the MAX1282/ MAX1283’s input architecture, which is composed of a T/H, input multiplexer, input comparator, switchedcapacitor DAC, and reference. In single-ended mode, the positive input (IN+) is connected to the selected input channel and the negative input (IN-) is set to COM. In differential mode, IN+ and IN- are selected from the following pairs: CH0/CH1 and CH2/CH3. Configure the channels according to Tables 1 and 2. The MAX1282/MAX1283 input configuration is pseudodifferential because only the signal at IN+ is sampled. The return side (IN-) is connected to the sampling capacitor while converting and must remain stable within ±0.5LSB (±0.1LSB for best results) with respect to GND during a conversion. If a varying signal is applied to the selected IN-, its amplitude and frequency must be limited to maintain accuracy. The following equations express the relationship between the maximum signal amplitude and its frequency to maintain ±0.5LSB accuracy. Assuming a CS SCLK DIN SHDN CH0 CH1 CH2 CH3 COM REF νIN − = (VIN − ) sin(2πft) The maximum voltage variation is determined by: max 13 7 2 3 4 5 d( νIN − ) dt = VIN − 2πf ≤ 1LSB VREF = 12 t CONV 2 t CONV A 0.65Vp-p, 60Hz signal at IN- will generate a ±0.5LSB error when using a +2.5V reference voltage and a 2.5µs conversion time (15 / fSCLK). When a DC reference voltage is used at IN-, connect a 0.1µF capacitor to GND to minimize noise at the input. During the acquisition interval, the channel selected as the positive input (IN+) charges capacitor CHOLD. The acquisition interval spans three SCLK cycles and ends on the falling SCLK edge after the input control word’s last bit has been entered. At the end of the acquisition interval, the T/H switch opens, retaining charge on CHOLD as a sample of the signal at IN+. The conversion interval begins with the input multiplexer switching CHOLD from IN+ to IN-. This unbalances node ZERO at the comparator’s input. The capacitive DAC adjusts during the remainder of the conversion cycle to restore node ZERO to VDD1 / 2 within the limits of 12-bit resolution. This action is equivalent to transferring a 12pF ✕ (VIN+ - VIN-) charge from CHOLD to the binaryweighted capacitive DAC, which in turn forms a digital representation of the analog input signal. 14 15 GND INPUT SHIFT REGISTER INT CLOCK CH0 CH1 OUTPUT SHIFT REGISTER ANALOG INPUT MUX CAPACITIVE DAC REF CONTROL LOGIC 11 12 DOUT SSTRB CH2 CH3 COM INPUT MUX CHOLD 12pF ZERO CSWITCH* CLOCK IN 12-BIT SAR ADC OUT REF 6 17k A ≈ 2.05 +2.500V Figure 3. Functional Diagram 16 10 9 8 HOLD 1 MAX1282 MAX1283 TRACK AT THE SAMPLING INSTANT, THE MUX INPUT SWITCHES FROM THE SELECTED IN+ CHANNEL TO THE SELECTED IN- CHANNEL. VDD1 VDD2 GND COMPARATOR RIN 800Ω 6pF T/H +1.22V REFERENCE REFADJ sinusoidal signal at IN-, the input voltage is determined by: VDD1/2 SINGLE-ENDED MODE: IN+ = CH0–CH3, IN- = COM. PSEUDO-DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS OF CH0/CH1 AND CH2/CH3. *INCLUDES ALL INPUT PARASITICS Figure 4. Equivalent Input Circuit ______________________________________________________________________________________ 11 MAX1282/MAX1283 Detailed Description MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference Table 1. Channel Selection in Single-Ended Mode (SGL/DIF = 1) SEL2 0 SEL1 0 SEL0 1 1 0 1 0 1 0 1 1 0 CH0 + CH1 CH2 CH3 COM – + – + – + – Table 2. Channel Selection in Pseudo-Differential Mode (SGL/DIF = 0) SEL2 SEL1 SEL0 CH0 CH1 0 0 1 + – 0 1 0 1 0 1 1 1 0 Track/Hold The T/H enters its tracking mode on the falling clock edge after the fifth bit of the 8-bit control word has been shifted in. It enters its hold mode on the falling clock edge after the eighth bit of the control word has been shifted in. If the converter is set up for single-ended inputs, IN- is connected to COM and the converter samples the “+” input. If the converter is set up for differential inputs, the difference of [(IN+) - (IN-)] is converted. At the end of the conversion, the positive input connects back to IN+ and CHOLD charges to the input signal. The time required for the T/H to acquire an input signal is a function of how quickly its input capacitance is charged. If the input signal’s source impedance is high, the acquisition time lengthens, and more time must be allowed between conversions. The acquisition time, tACQ, is the maximum time the device takes to acquire the signal and the minimum time needed for the signal to be acquired. It is calculated by the following equation: tACQ = 9 ✕ (RS + RIN) ✕ 18pF where RIN = 800Ω and RS = the source impedance of the input signal; t ACQ is never less than 400ns (MAX1282) or 625ns (MAX1283). Note that source impedances below 2kΩ do not significantly affect the ADC’s AC performance. Input Bandwidth The ADC’s input tracking circuitry has a 6MHz (MAX1282) or 3MHz (MAX1283) small-signal bandwidth, so it is possible to digitize high-speed transient 12 – CH2 CH3 + – – + + events and measure periodic signals with bandwidths exceeding the ADC’s sampling rate by using undersampling techniques. To avoid high-frequency signals being aliased into the frequency band of interest, antialias filtering is recommended. Analog Input Protection Internal protection diodes, which clamp the analog input to VDD1 and GND, allow the channel input pins to swing from GND - 0.3V to V DD1 + 0.3V without damage. However, for accurate conversions near full scale, the inputs must not exceed VDD1 by more than 50mV or be lower than GND by 50mV. If the analog input exceeds 50mV beyond the supplies, do not allow the input current to exceed 2mA. Starting a Conversion Start a conversion by clocking a control byte into DIN. With CS low, each rising edge on SCLK clocks a bit from DIN into the MAX1282/MAX1283’s internal shift register. After CS falls, the first arriving logic “1” bit defines the control byte’s MSB. Until this first “start” bit arrives, any number of logic “0” bits can be clocked into DIN with no effect. Table 3 shows the control-byte format. The MAX1282/MAX1283 are compatible with SPI/ QSPI/MICROWIRE devices. For SPI, select the correct clock polarity and sampling edge in the SPI control registers: set CPOL = 0 and CPHA = 0. MICROWIRE, SPI, and QSPI all transmit a byte and receive a byte at the same time. Using the Typical Operating Circuit, the simplest software interface requires only three 8-bit transfers to perform a conversion (one 8-bit transfer to configure the ADC, and two more 8-bit transfers to clock out the ______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference Simple Software Interface Make sure the CPU’s serial interface runs in master mode so the CPU generates the serial clock. Choose a clock frequency from 500kHz to 6.4MHz (MAX1282) or 4.8MHz (MAX1283). 1) Set up the control byte and call it TB1. TB1 should be in the format: 1XXXXXXX binary, where the Xs denote the particular channel, selected conversion mode, and power mode. 2) Use a general-purpose I/O line on the CPU to pull CS low. 3) Transmit TB1 and, simultaneously, receive a byte and call it RB1. Ignore RB1. 4) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB2. 5) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB3. 6) Pull CS high. Figure 5 shows the timing for this sequence. Bytes RB2 and RB3 contain the result of the conversion, padded with three leading zeros, and one trailing zero. The total conversion time is a function of the serial-clock frequency and the amount of idle time between 8-bit transfers. To avoid excessive T/H droop, make sure the total conversion time does not exceed 120µs. Data Framing The falling edge of CS does not start a conversion. The first logic high clocked into DIN is interpreted as a start bit and defines the first bit of the control byte. A conversion starts on SCLK’s falling edge, after the eighth bit of the control byte (the PD0 bit) is clocked into DIN. The start bit is defined as follows: The first high bit clocked into DIN with CS low any time the converter is idle, e.g., after VDD1 and VDD2 are applied. or The first high bit clocked into DIN after B6 of a conversion in progress is clocked onto the DOUT pin (Figure 7). Once a start bit has been recognized, the current conversion may only be terminated by pulling SHDN low. The fastest the MAX1282/MAX1283 can run with CS held low between conversions is 16 clocks per conversion. Figure 7 shows the serial-interface timing necessary to perform a conversion every 16 SCLK cycles. If CS is tied low and SCLK is continuous, guarantee a start bit by first clocking in 16 zeros. ___________Applications Information Power-On Reset Serial Clock When power is first applied, and if SHDN is not pulled low, internal power-on reset circuitry activates the MAX1282/MAX1283 in normal operating mode, ready to convert with SSTRB = low. After the power supplies stabilize, the internal reset time is 10µs, and no conversions should be performed during this phase. If CS is low, the first logic 1 on DIN is interpreted as a start bit. Until a conversion takes place, DOUT shifts out zeros. Additionally, wait for the reference to stabilize when using the internal reference. The external clock not only shifts data in and out, but it also drives the analog-to-digital conversion steps. SSTRB pulses high for one clock period after the last bit of the control byte. Successive-approximation bit decisions are made and appear at DOUT on each of the next 12 SCLK rising edges, MSB first (Figure 5). SSTRB and DOUT go into a high-impedance state when CS goes high; after the next CS falling edge, SSTRB outputs a logic low. Figure 6 shows the detailed serial-interface timings. The conversion must complete in 120µs or less, or droop on the sample-and-hold capacitors may degrade conversion results. Save power by placing the converter in one of two lowcurrent operating modes or in full power-down between conversions. Select the power-down mode through bit 1 and bit 0 of the DIN control byte (Tables 3 and 4), or force the converter into hardware shutdown by driving SHDN to GND. The software power-down modes take effect after the conversion is completed; SHDN overrides any software power mode and immediately stops any conversion in progress. In software power-down mode, the serial interface remains active while waiting for a new control byte to start conversion and switch to full-power mode. Digital Output In unipolar input mode, the output is straight binary (Figure 13). For bipolar input mode, the output is two’s complement (Figure 14). Data is clocked out on the rising edge of SCLK in MSB-first format. Power Modes ______________________________________________________________________________________ 13 MAX1282/MAX1283 conversion result). (See Figure 16 for MAX1282/ MAX1283 QSPI connections.) MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference Table 3. Control-Byte Format BIT 7 (MSB) BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 (LSB) START SEL2 SEL1 SEL0 UNI/BIP SGL/DIF PD1 PD0 BIT NAME DESCRIPTION 7(MSB) START The first logic 1 bit after CS goes low defines the beginning of the control byte. 6 5 4 SEL2 SEL1 SEL0 These three bits select which of the eight channels are used for the conversion (Tables 1 and 2). 3 UNI/BIP 1 = unipolar, 0 = bipolar. Selects unipolar or bipolar conversion mode. In unipolar mode, an analog input signal from 0 to VREF can be converted; in bipolar mode, the differential signal can range from -VREF/2 to +VREF/2. 2 SGL/DIF 1 = single ended, 0 = pseudo-differential. Selects single-ended or pseudo-differential conversions. In single-ended mode, input signal voltages are referred to COM. In pseudo-differential mode, the voltage difference between two channels is measured (Tables 1 and 2). 1 0(LSB) PD1 PD0 Select operating mode. PD1 PD0 Mode 0 0 Full power-down 0 1 Fast power-down 1 0 Reduced power 1 1 Normal operation Table 4. Software-Controlled Power Modes TOTAL SUPPLY CURRENT PD1/PD0 MODE CIRCUIT SECTIONS* CONVERTING (mA) AFTER CONVERSION INPUT COMPARATOR REFERENCE 00 Full Power-Down (FULLPD) 2.5 2µA Off Off 01 Fast Power-Down (FASTPD) 2.5 0.9mA Reduced Power On 10 Reduced-Power Mode (REDP) 2.5 1.3mA Reduced Power On 11 Normal Operating 2.5 2.0mA Full Power On *Circuit operation between conversions; during conversion all circuits are fully powered up. Once conversion is completed, the device goes into the programmed power mode until a new control byte is written. The power-up delay is dependent on the power-down state. Software low-power modes will be able to start conversion immediately when running at decreased clock rates (see Power-Down Sequencing). Upon power-on reset, when exiting software full power-down mode, or when exiting hardware shutdown, the device goes immediately into full-power mode and is ready to 14 convert after 2µs when using an external reference. When using the internal reference, wait for the typical power-up delay from a full power-down (software or hardware) as shown in Figure 8. Software Power-Down Software power-down is activated using bits PD1 and PD0 of the control byte. When software power-down is asserted, the ADC completes the conversion in ______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference MAX1282/MAX1283 CS tACQ SCLK 1 4 8 9 12 16 20 24 SEL SEL SEL UNI/ SGL/ 2 1 0 BIP DIF PD2 PD2 DIN START SSTRB RB1 RB2 RB3 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 DOUT A/D STATE IDLE 400ns CONVERSION IDLE (CLK = 6.4MHz) Figure 5. Single-Conversion Timing progress and powers down into the specified low-quiescent-current state (2µA, 0.9mA, or 1.3mA). and power-down modes may attain the lowest power consumption in other applications. The first logic 1 on DIN is interpreted as a start bit and puts the MAX1282/MAX1283 into its full-power mode. Following the start bit, the data input word or control byte also determines the next power-down state. For example, if the DIN word contains PD1 = 0 and PD0 = 1, a 0.9mA power-down resumes after one conversion. Table 4 details the four power modes with the corresponding supply current and operating sections. Using Full Power-Down Mode Full power-down mode (FULLPD) achieves the lowest power consumption, up to 1000 conversions per channel per second. Figure 9a shows the MAX1283’s power consumption for one- or four-channel conversions utilizing full power-down mode (PD1 = PD0 = 0), with the internal reference and conversion controlled at the maximum clock speed. A 0.01µF bypass capacitor at REFADJ forms an RC filter with the internal 17kΩ reference resistor, with a 170µs time constant. To achieve full 12-bit accuracy, nine time constants or 1.5ms are required after power-up if the bypass capacitor is fully discharged between conversions. Waiting this 1.5ms duration in fast power-down (FASTPD) or reducedpower (REDP) mode instead of in full power-up can further reduce power consumption. This is achieved by using the sequence shown in Figure 11a. Figure 9b shows the MAX1283’s power consumption for one- or four-channel conversions utilizing FULLPD mode (PD1 = PD0 = 0), with an external reference and conversion controlled at the maximum clock speed. One dummy conversion to power up the device is needed, but no waiting time is necessary to start the second conversion, thereby achieving lower power consumption as low as half the full sampling rate. Hardware Power-Down Pulling SHDN low places the converter in hardware power-down. Unlike software power-down mode, the conversion is not completed; it stops coincidentally with SHDN being brought low. When returning to normal operation—from SHDN, with an external reference—the MAX1282/MAX1283 can be considered fully powered up within 2µs of actively pulling SHDN high. When using the internal reference, the conversion should be initiated only when the reference has settled; its recovery time is dependent on the external bypass capacitors and the time between conversions. Power-Down Sequencing The MAX1282/MAX1283 auto power-down modes can save considerable power when operating at less than maximum sample rates. Figures 9 and 10 show the average supply current as a function of the sampling rate. The following sections discuss the various powerdown sequences. Other combinations of clock rates ______________________________________________________________________________________ 15 MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference CS tCSW tCSS tCP tCH tCSO tCSH tCS1 tCL #10 SCLK tDH tDS tDOH DIN tDOV tDOD tDOE DOUT tSTH tSTV tSTE tSTD SSTRB Figure 6. Detailed Serial-Interface Timing Using Fast Power-Down and Reduced-Power Modes FASTPD and REDP modes achieve the lowest power consumption at speeds close to the maximum sampling rate. Figure 10 shows the MAX1283’s power consumption in FASTPD mode (PD1 = 0, PD0 = 1), REDP mode (PD1 = 1, PD0 = 0), and, for comparison, normal operating mode (PD1 = 1, PD0 = 1). The figure shows power consumption using the specified powerdown mode, with the internal reference and conversion controlled at the maximum clock speed. The clock speed in FASTPD or REDP should be limited to 4.8MHz for the MAX1282/MAX1283. FULLPD mode may provide increased power savings in applications where the MAX1282/MAX1283 are inactive for long periods of time, but intermittent bursts of high-speed conversions are required. Figure 11b shows FASTPD and REDP timing. Internal and External References The MAX1282/MAX1283 can be used with an internal or external reference voltage. An external reference can be connected directly at REF or at the REFADJ pin. An internal buffer is designed to provide 2.5V at REF for the MAX1282/MAX1283. The internally trimmed 1.22V reference is buffered with a 2.05 gain. Internal Reference The MAX1282/MAX1283’s full-scale range with the internal reference is 2.5V with unipolar inputs and ±1.25V with bipolar inputs. The internal reference voltage is adjustable by ±100mV with the circuit in Figure 12. External Reference The MAX1282/MAX1283’s external reference can be placed at the input (REFADJ) or the output (REF) of the internal reference-buffer amplifier. The REFADJ input impedance is typically 17kΩ. At REF, the DC input resistance is a minimum of 18kΩ. During conversion, an external reference at REF must deliver up to 350µA DC load current and have 10Ω or less output impedance. If the reference has a higher output impedance or is noisy, bypass it close to the REF pin with a 4.7µF capacitor. Table 5. Full Scale and Zero Scale UNIPOLAR MODE Full Scale VREF + VCOM 16 BIPOLAR MODE Zero Scale VCOM Positive Full Scale Zero Scale Negative Full Scale VREF / 2 + VCOM VCOM VREF / 2 + VCOM ______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference MAX1282/MAX1283 CS DIN S CONTROL BYTE 0 1 S CONTROL BYTE 1 8 12 16 1 5 8 S CONTROL BYTE 2 12 16 1 5 S 8 12 ETC 16 1 5 SCLK B11 DOUT B6 B0 CONVERSION RESULT 0 B11 B6 B0 CONVERSION RESULT 1 B11 B6 SSTRB Figure 7. Continuous 16-Clock/Conversion Timing 10k MAX1283, VDD1 = VDD 2 = 3.0V CLOAD = 20pF CODE = 101010000000 1.25 SUPPLY CURRENT (µA) REFERENCE POWER-UP DELAY (ms) 1.50 1.00 0.75 0.50 1k 4 CHANNELS 100 1 CHANNEL 10 0.25 0 0.0001 1 0.001 0.01 0.1 1 1 10 10 Figure 8. Reference Power-Up Delay vs. Time in Shutdown 1k 10k 100k Figure 9b. Average Supply Current vs. Conversion Rate with External Reference in FULLPD 1k 2.5 MAX1283, VDD1 = VDD2 = 3.0V CLOAD = 20pF CODE = 101010000000 NORMAL OPERATION SUPPLY CURRENT (mA) SUPPLY CURRENT (µA) 100 SAMPLING RATE (sps) TIME IN SHUTDOWN (s) 100 4 CHANNELS 10 1 CHANNEL 1 2.0 REDP FASTPD 1.5 1.0 MAX1283, VDD1 = VDD2 = 3.0V CLOAD = 20pF CODE = 101010000000 0.5 0.1 1 10 100 1k 10k SAMPLING RATE (sps) Figure 9a. Average Supply Current vs. Conversion Rate with Internal Reference in FULLPD 0 50 100 150 200 250 300 350 SAMPLING RATE (sps) Figure 10. Average Supply Current vs. Sampling Rate (in FASTPD, REDP, and Normal Operation) ______________________________________________________________________________________ 17 MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference To use the direct REF input, disable the internal buffer by connecting REFADJ to VDD1. Using the REFADJ input makes buffering the external reference unnecessary. Figure 15 shows the recommended system ground connections. Establish a single-point analog ground (star ground point) at GND. Connect all other analog grounds to the star ground. Connect the digital system ground to this ground only at this point. For lowestnoise operation, the ground return to the star ground’s power supply should be low impedance and as short as possible. High-frequency noise in the VDD1 power supply may affect the high-speed comparator in the ADC. Bypass the supply to the star ground with 0.1µF and 10µF capacitors close to VDD1 of the MAX1282/MAX1283. Minimize capacitor lead lengths for best supply-noise rejection. If the power supply is very noisy, a 10Ω resistor can be connected as a lowpass filter (Figure 15). Transfer Function Table 5 shows the full-scale voltage ranges for unipolar and bipolar modes. Figure 13 depicts the nominal, unipolar input/output (I/O) transfer function, and Figure 14 shows the bipolar I/O transfer function. Code transitions occur halfway between successive-integer LSB values. Output coding is binary, with 1LSB = 0.61mV (2.500V / 4096) for unipolar operation, and 1LSB = 0.61mV [(2.500V / 2) / 4096] for bipolar operation. Layout, Grounding, and Bypassing For best performance, use PC boards; wire-wrap boards are not recommended. Board layout should ensure that digital and analog signal lines are separated from each other. Do not run analog and digital (especially clock) lines parallel to one another, or digital lines underneath the ADC package. High-Speed Digital Interfacing with QSPI The MAX1282/MAX1283 can interface with QSPI using the circuit in Figure 16 (CPOL = 0, CPHA = 0). This QSPI circuit can be programmed to do a conversion on each of the four channels. The result is stored in memory without taxing the CPU, since QSPI incorporates its own microsequencer. WAIT 2ms (10 x RC) 0 0 1 DIN 1 0 1 REDP FULLPD 0 0 1 FULLPD DUMMY CONVERSION 1.22V 1 1.22V RE FADJ 0V γ = RC = 17kΩ x 0.01µF 2.5V 2.5V REF 0V 2.5mA IVDD1 + IVDD2 2.5mA 2.5mA 1.3mA OR 0.9mA 0mA 0mA Figure 11a. Full Power-Down Timing 1 0 1 DIN REF 1 0 1 REDP REDP 0 1 1 FASTPD 2.5V (ALWAYS ON) 2.5mA IVDD1 + IVDD2 2.5mA 0.9mA 2.5mA 0.9mA 1.3mA Figure 11b. FASTPD and REDP Timing 18 ______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference MAX1282/MAX1283 +3.3V OUTPUT CODE 24k MAX1282 MAX1283 510k 100k 12 011 . . . 111 FS = VREF + VCOM 2 011 . . . 110 ZS = VCOM REFADJ 000 . . . 010 000 . . . 001 0.047µF -FS = -VREF + VCOM 2 1LSB = 000 . . . 000 VREF 4096 111 . . . 111 111 . . . 110 Figure 12. MAX1282/MAX1283 Reference-Adjust Circuit OUTPUT CODE 111 . . . 101 100 . . . 001 100 . . . 000 FULL-SCALE TRANSITION 11 . . . 111 - FS 11 . . . 110 +FS - 1LSB INPUT VOLTAGE (LSB) 11 . . . 101 *VCOM ≤ VREF / 2 FS = VREF + VCOM ZS = VCOM V 1LSB = REF 4096 00 . . . 011 00 . . . 010 00 . . . 001 00 . . . 000 0 1 (COM) COM* 2 3 FS INPUT VOLTAGE (LSB) FS - 3/2LSB Figure 13. Unipolar Transfer Function, Full Scale (FS) = VREF + VCOM, Zero Scale (ZS) = VCOM TMS320LC3x Interface Figure 17 shows an application circuit to interface the MAX1282/MAX1283 to the TMS320 in external clock mode. The timing diagram for this interface circuit is shown in Figure 18. Use the following steps to initiate a conversion in the MAX1282/MAX1283 and to read the results: 1) The TMS320 should be configured with CLKX (transmit clock) as an active-high output clock and CLKR (TMS320 receive clock) as an active-high input clock. CLKX and CLKR on the TMS320 are connected to the MAX1282/MAX1283’s SCLK input. Figure 14. Bipolar Transfer Function, Full Scale (FS) = VREF / 2 + VCOM, Zero Scale (ZS) = VCOM 2) The MAX1282/MAX1283’s CS pin is driven low by the TMS320’s XF_ I/O port to enable data to be clocked into the MAX1282/MAX1283’s DIN pin. 3) An 8-bit word (1XXXXX11) should be written to the MAX1282/MAX1283 to initiate a conversion and place the device into normal operating mode. See Table 3 to select the proper XXXXX bit values for your specific application. 4) The MAX1282/MAX1283’s SSTRB output is monitored through the TMS320’s FSR input. A falling edge on the SSTRB output indicates that the conversion is in progress and data is ready to be received from the device. 5) The TMS320 reads in 1 data bit on each of the next 16 rising edges of SCLK. These data bits represent the 12-bit conversion result followed by 4 trailing bits, which should be ignored. 6) Pull CS high to disable the MAX1282/MAX1283 until the next conversion is initiated. ______________________________________________________________________________________ 19 MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference Signal-to-Noise Ratio (SNR) For a waveform perfectly reconstructed from digital samples, the SNR is the ratio of the full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-to-digital noise is caused only by quantization error and results directly from the ADC’s resolution (N bits): SUPPLIES +3V +3V GND SNR = (6.02 *R = 10Ω VDD1 GND COM VDD2 +3V DGND DIGITAL CIRCUITRY MAX1282 MAX1283 ✕ N + 1.76)dB In reality, there are other noise sources besides quantization noise, including thermal noise, reference noise, clock jitter, etc. Therefore, SNR is calculated by taking the ratio of the RMS signal to the RMS noise, which includes all spectral components minus the fundamental, the first five harmonics, and the DC offset. Signal-to-Noise Plus Distortion (SINAD) SINAD is the ratio of the fundamental input frequency’s RMS amplitude to RMS equivalent of all other ADC output signals: *OPTIONAL Figure 15. Power-Supply Grounding Connection Definitions Integral Nonlinearity Integral nonlinearity (INL) is the deviation of the values from a straight line on an actual transfer function. This straight line can be a best-straight-line fit or a line drawn between the endpoints of the transfer function, once offset and gain errors have been nullified. The static linearity parameters for the MAX1282/MAX1283 are measured using the best straight-line fit method. Differential Nonlinearity Differential nonlinearity (DNL) is the difference between an actual step width and the ideal value of 1LSB. A DNL error specification of less than 1LSB guarantees no missing codes and a monotonic transfer function. Aperture Width Aperture width (tAW) is the time the T/H circuit requires to disconnect the hold capacitor from the input circuit (for instance, to turn off the sampling bridge, and put the T/H unit in hold mode). Aperture Jitter Aperture jitter (tAJ) is the sample-to-sample variation in the time between the samples. Aperture Delay SINAD (dB) = 20 ✕ log (SignalRMS / NoiseRMS) Effective Number of Bits (ENOB) ENOB indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADC’s error consists only of quantization noise. With an input range equal to the ADC’s full-scale range, calculate ENOB as follows: ENOB = (SINAD - 1.76) / 6.02 Total Harmonic Distortion (THD) THD is the ratio of the RMS sum of the input signal’s first five harmonics to the fundamental itself. This is expressed as: 2 2 2 2 2 V2 + V3 + V4 + V4 + V5 THD = 20 × log V1 where V1 is the fundamental amplitude, and V2 through V5 are the amplitudes of the 2nd- through 5th-order harmonics. Spurious-Free Dynamic Range (SFDR) SFDR is the ratio of the RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next-largest distortion component. Aperture delay (tAD) is the time defined between the rising edge of the sampling clock and the instant when an actual sample is taken. 20 ______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference 10µF MAX1282/MAX1283 +5V OR +3V +5V OR +3V 0.1µF 1 VDD1 VDD2 16 2 CH0 SCLK 15 0.1µF 10µF (POWER SUPPLIES) SCK 3 CH1 ANALOG INPUTS MAX1282 MAX1283 CSB 14 4 CH2 DIN 13 5 CH3 SSTRB 12 6 COM DOUT 11 7 SHDN GND 10 PCS0 MOSI MC683XX MISO VDD1 4.7µF REFADJ 9 8 REF 0.01µF (GND) Figure 16. QSPI Connections XF CLKX CS SCLK TMS320LC3x MAX1282 MAX1283 CLKR DX DIN DR DOUT FSR SSTRB Figure 17. MAX1282/MAX1283-to-TMS320 Serial Interface ______________________________________________________________________________________ 21 MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference CS SCLK START DIN SSTRB SEL2 SEL1 SEL0 UNI/BIP SGI/DIF PD1 PD0 HIGH IMPEDANCE DOUT MSB B10 B1 B0 HIGH IMPEDANCE Figure 18. MAX1282/MAX1283-to-TMS320 Serial Interface Chip Information Typical Operating Circuit TRANSISTOR COUNT: 4286 +5V OR +3V CH0 0 TO +2.5V ANALOG INPUTS VDD1 VDD2 MAX1282 GND MAX1283 CH3 REF 4.7µF CS SCLK REFADJ DOUT SSTRB SHDN 22 CPU COM DIN 0.01µF PROCESS: BiCMOS VDD 0.1µF I/O SCK (SK) MOSI (SO) MISO (SI) VSS ______________________________________________________________________________________ 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference TSSOP.EPS Note: The MAX1282/MAX1283 do not have an exposed die pad. ______________________________________________________________________________________ 23 MAX1282/MAX1283 ________________________________________________________Package Information MAX1282/MAX1283 300ksps/400ksps, Single-Supply, 4-Channel, Serial 12-Bit ADCs with Internal Reference NOTES Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.