ADC16471CIN

ADC16071 ADC16471 16-Bit Delta-Sigma 192 ks s Analog-to-Digital Converters February 1995 ADC16071 ADC16471 16-Bit Delta-Sigma 192 ks s Analog-to-Digital Converters General Description The ADC16071 ADC16471 are 16-bit delta-sigma analogto-digital converters using 64 c oversampling at 12 288 MHz A 5th-order comb filter and a 246 tap FIR decimation filter are used to achieve an output data rate of up to 192 kHz The combination of oversampling and internal digital filtering greatly reduces the external anti-alias filter requirements to a simple RC low pass filter The FIR filters offer linear phase response 0 005 dB passband ripple and t 90 dB stopband rejection The ADC16071 ADC16471’s analog fourth-order modulator uses switched capacitor technology A built-in fully-differential bandgap voltage reference is also included in the ADC16471 The ADC16071 has no internal reference and requires externally applied reference voltages The ADC16071 ADC16471 use an advanced BiCMOS process for a low power consumption of 500 mW (max) while operating from a single 5V supply A power-down mode reduces the power supply current from 100 mA (max) in the active mode to 1 3 mA (max) The ADC16071 ADC16471 are ideal analog-to-digital front ends for signal processing applications They provide a complete high resolution signal acquisition system that requires a minimal external anti-aliasing filter reference or interface logic The ADC16071 ADC16471’s serial interface is compatible with the DSP56001 TMS320 and ADSP2100 digital signal processors Key Specifications Y Y Y Y Resolution Total harmonic distortion 48 kHz output data rate 192 kHz output data rate Maximum output data rate Power dissipation Active 192 kHz output data rate 48 kHz output data rate Power-down 16 bits b 94 dB (typ) b 80 dB (typ) 192 kHz (min) 500 mW (max) 275 mW (max) 6 5 mW (max) Key Features Y Y Y Y Y Y Y Y Voltage reference (ADC16471 only) Fourth-order modulator 64 c oversampling with a 12 288 MHz sample rate Adjustable output data rate from 7 kHz to 192 kHz Linear-phase digital anti-aliasing filter 0 005 dB passband ripple 90 dB stopband rejection Single a 5V supply Power-down mode Serial data interface compatible with popular DSP devices Applications Y Y Y Y Y Y Medical instrumentation Process control systems Test equipment High sample-rate audio Digital Signal Processing (DSP) analog front-end Vibration and noise analysis Connection Diagram Ordering Information Part No ADC16471CIN ADC16471CIWM ADC16071CIN ADC16071CIWM Package 24-Pin Molded DIP 24-Pin SOIC 24-Pin Molded DIP 24-Pin SOIC NS Package No N24C M24B N24C M24B TL H 11454 – 2 TRI-STATE is a registered trademark of National Semiconductor Corporation C1995 National Semiconductor Corporation TL H 11454 RRD-B30M75 Printed in U S A Block Diagram ADC16471 TL H 11454 – 1 ADC16071 TL H 11454 – 22 2 Absolute Maximum Ratings (Notes 1 and 2) If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Supply Voltage (VA a VD a and VM a ) Logic Control Inputs Voltage at Other Inputs and Outputs a 6 5V b 0 3V to VD a a 0 3V ESD Susceptibility (Note 5) Human Body Model Machine Model 4000V 250V See AN-450 ‘‘Surface Mounting Methods and Their Effect on Product Reliability’’ for other methods of soldering surface mount devices b 0 3V to VA a e VM a a 0 3V g 25 mA Input Current at Any Pin (Note 3) g 100 mA Package Input Current (Note 3) Maximum Junction Temperature (Note 4) 150 C b 65 C to a 150 C Storage Temperature Lead Temperature N Package (Soldering 10 sec ) 300 C WM Package (Infrared 15 sec ) 220 C WM Package (Vapor Phase 60 sec ) 215 C Operating Ratings (Notes 1 and 2) Temperature Range (Tmin s TA s Tmax) b 40 C s TA s a 85 C ADC16471CIN ADC16071CIN ADC16471CIWM ADC16071CIWM Supply Voltage VA a VD a VM a 4 75V to 5 25V Converter Electrical Characteristics The following specifications apply for VM a e VA a e VD a e 5 0VDC VMID e VA a 2 e 2 50V VREF a e VMID a 1 25V VREFb e VMID b 1 25V fCLK e 24 576 MHz and dynamic tests are performed with an input signal magnitude set at b6 dB with respect to a full-scale input unless otherwise specified Boldface limits apply for TA e TJ e Tmin to Tmax all other limits TA e TJ e 25 C Symbol Resolution fCLK e 24 576 MHz (fs e 192 kHz) S (N a D) THD IMD Signal-to-Noise a Distortion Ratio Total Harmonic Distortion Intermodulation Distortion Converter Noise Floor (Note 8) fCLK e 6 144 MHz (fs e 48 kHz) S (N a D) THD IMD Signal-to-Noise a Distortion Ratio Total Harmonic Distortion Intermodulation Distortion Converter Noise Floor (Note 8) OTHER CONVERTER CHARACTERISTICS ZIN D AV VOS IA IM ID ISPD PD VMID 3 Input Impedance (Note 9) Gain Error Input Offset Voltage Analog Power Supply Current Modulator Power Supply Current Digital Power Supply Current Power-Down Supply Current Power Dissipation fCLK e 24 576 MHz fCLK e 6 144 MHz fCLK e 24 576 MHz fCLK e 6 144 MHz IA a ID a IM 34 g0 2 g1 0 Parameter Conditions Typical (Note 6) Limits (Note 7) 16 Units (Limit) Bits Measurement bandwidth e 0 45fs fIN e 19 kHz fIN e 19 kHz f1 e 18 5 kHz f2 e 19 5 kHz Measurement Bandwidth e 0 45fs 76 0 010 0 010 b 88 72 0 022 0 017 b 77 dB (min) % (max) % (max) dBFS (min) Measurement bandwidth e 0 45fs fIN e 5 kHz fIN e 5 kHz f1 e 4 kHz f2 e 5 5 kHz Measurement Bandwidth e 0 45fs 85 0 002 0 003 b 99 80 73 0 0055 0 008 0 009 0 01 b 92 b 89 dB (min) dB (min) % (max) % (max) % (max) % (max) dBFS (min) dBFS (min) kX %FS (max) mV 31 24 08 65 23 13 05 mA (max) mA (max) mA (max) mA W V 15 23 16 04 50 13 0 25 0 375 VA a 2 Digital Filter Characteristics The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified Boldface limits apply for TA e TJ e Tmin to Tmax all other limits TA e TJ e 25 C Symbol Parameter Stopband Rejection Passband Ripple 3 dB Cutoff Frequency Data Latency Conditions Typical (Note 6) b 90 0 g 0 005 Limits (Note 7) Units (Limit) dB dB fs Clock Cycles 0 45 3 968 Reference Characteristics (ADC16471 Only) The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified Boldface limits apply for TA e TJ e Tmin to Tmax all other limits TA e TJ e 25 C Symbol VREF a VREFb D(VREF a – VREFb) DT DVREF a DI DVREFb DI Parameter Positive Internal Reference Output Voltage Negative Internal Reference Output Voltage Internal Reference Temperature Coefficient Positive Internal Reference Load Regulation Negative Internal Reference Load Regulation Sourcing (0 mA s I s a 10 mA) Sinking (b1 mA s I s 0 mA) Sinking (b1 mA s I s 0 mA) Sourcing (0 mA s I s 10 mA) Conditions Typical (Note 6) VMID a 1 25 VMID b 1 25 30 34 32 60 mV (max) 60 Limits (Note 7) VMID a 1 175 VMID a 1 325 VMID b 1 325 VMID b 1 175 Units (Limit) V (min) V (max) V (min) V (max) ppm C Input Reference Characteristics (ADC16071 Only) The following specifications apply for VA a e VD a e VM a e 5V Symbol VREF a VREFb VREF a – VREFb Parameter Positive Reference Voltage Negative Reference Voltage Total Reference Voltage Conditions Typical (Note 6) 1 VA a 0 VA a b 1 1 VA a Limits (Note 7) Units V V V V V V 4 DC Electrical Characteristics The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified Boldface limits apply for TA e TJ e TMIN to TMAX all other limits TA e TJ e 25 C Symbol VIH VIL VOH VOL IIN(1) IIN(0) ITSI CIN Parameter Logic High Input Voltage Logic Low Input Voltage Logic High Output Voltage Logic Low Output Voltage Logical ‘‘1’’ Input Current Logical ‘‘0’’ Input Current SDO TRI-STATE Leakage Current Logic Input Capacitance VIN e 0 4V to 2 4V VIN e 0 to VD a Conditions VD a e 5 25V VD a e 4 75V Logic High Output Current e b400 mA VD a e 4 75V Logic Low Output Current e 2 mA VD a e 5 25V 10 b1 0 Typical (Note 6) Limits (Note 7) VD a 23 08 b0 3 Units (Limit) V (max) V (min) V (max) V (min) V (min) V (max) mA (max) mA (max) mA (max) pF 24 05 50 b5 0 10 5 50 AC Electrical Characteristics for Clock In (CLK) Serial Clock Out (SCO) and Frame Sync In (FSI) The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified Boldface limits apply for TA e TJ e TMIN to TMAX all other limits TA e TJ e 25 C Symbol fCLK tCLK tCLKL tCLKH tR tF tFSILOW Parameter CLK Frequency Range (fCLK e 1 tCLK) CLK Period (tCLK e 1 fCLK) CLK Low Pulse Width CLK High Pulse Width CLK Rise Time CLK Fall Time Minimum Frame Sync Input Low Time before Frame Sync Input Asserted High Frame Sync Input Setup Time Frame Sync Input Hold Time Serial Clock Output Delay Time from Rising Edge of CLK Serial Clock Output Period 12 Conditions Typical (Note 6) Limits (Note 7) 25 1 1000 40 16 14 10 3 10 3 2 10 10 20 5 4 Units (Limit) MHz (max) MHz (min) ns (max) ns (min) ns (min) ns (min) ns (max) ns (min) ns (max) ns (min) tCLK (min) ns (min) ns (min) ns (max) ns (min) tCLK tFSISU tFSIH tSCOD tSCO 5 AC Electrical Characteristics for Frame Sync Out (FSO) Serial Clock Out (SCO) and Serial Data Out (SDO) The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified Boldface limits apply for TA e TJ e TMIN to TMAX all other limits TA e TJ e 25 C Symbol tSCOFSOH tSCOFSOL tSDOV tFSIFSOL Parameter Delay from Serial Clock Out to Frame Sync Output High Delay from Serial Clock Out to Frame Sync Output Low Delay from Serial Clock Out to Serial Data Output Valid Delay from Frame Sync Input to Frame Sync Output Low Conditions Typical (Note 6) 2 2 3 Limits (Note 7) 5 5 8 8 Units (Limit) ns (max) ns (max) ns (max) tCLK (max) AC Electrical Characteristics for Data Output Enable (DOE) The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified Boldface limits apply for TA e TJ e TMIN to TMAX all other limits TA e TJ e 25 C Symbol tDOEE tDOED Parameter Data Output Enable Delay Time Data Output Disable Delay Time Conditions Typical (Note 6) 20 16 Limits (Note 7) 25 20 Units (Limit) ns (max) ns (max) Note 1 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits For guaranteed specifications and test conditions see the Electrical Characteristics The guaranteed specifications apply for the test conditions listed Some performance characteristics may degrade when the device is not operated under the listed test conditions Note 2 All voltages are measured with respect to GND unless otherwise specified Note 3 When the input voltage (VIN) at any pin exceeds the power supply rails (VIN k GND or VIN l (VA a VM a or VD a )) the current at that pin should be limited to 25 mA The 100 mA maximum package input current rating allows the voltage at any four pins with an input current of 25 mA each to simultaneously exceed the power supply voltages Note 4 The maximum power dissipation is a function of the maximum junction temperature (TJ(MAX)) total thermal resistance (iJA) and ambient temperature (TA) The maximum allowable power dissipation at any ambient temperature is PD(max) e (TJ(max) b TA) iJA When board mounted the ADC16071 ADC16471’s typical thermal resistance is Order Number ADC16071CIN ADC16471CIN ADC16071CIWM ADC16471CIWM iJA 47 C W 72 C W Note 5 Human body model 100 pF discharge through a 1 5 kX resistor The machine model is a 200 pF capacitor discharged directly into each pin Note 6 Typicals are at TA e 25 C and represent most likely parametric norm Note 7 Limits are guaranteed to National’s AOQL (Average Output Quality Level) Note 8 The VIN a pin is shorted to the VINb pin Note 9 The input impedance between VIN a and VINb due to the effective resistance of the switch capacitor input varies as follows 1012 ZIN e fCLK 2 35 ( ) 2 6 Typical Performance Characteristics S (N a D) vs VIN Amplitude S (N a D) vs Output Data Rate (fs) S (N a D) vs Temperature Spectral Response fs e 192 kHz fIN e 20 kHz Spectral Response fs e 192 kHz fIN e 80 kHz Spectral Response fs e 48 kHz fIN e 5 kHz Analog Supply Current (IA a IM) vs Temperature Digital Supply Current ID vs Temperature Analog Supply Current (IA a IM) vs Output Data Rate (fs) Digital Supply Current (ID) vs Output Data Rate (fs) Frequency Response of Digital Filter TL H 11454 – 24 7 TL H 11454 – 8 FIGURE 1 Timing Diagrams for Clock Input (CLK) Frame Sync Input (FSI) and Serial Clock Output (SCO) 8 9 TL H 11454 – 4 FIGURE 2 Detailed Timing Diagrams for Frame Sync Input (FSI) Frame Sync Out (FSO) Serial Clock Out (SCO) and Serial Data Out (SDO) 10 TL H 11454 – 5 FIGURE 3 Timing Diagrams for Frame Sync Out (FSO) Serial Clock Out (SCO) and Serial Data Out (SDO) 11 TL H 11454 – 6 FIGURE 4 Master Slave Mode Timing Diagrams TL H 11454 – 7 FIGURE 5 Timing Diagrams for Data Output Enable (DOE) and Serial Data Out (SDO) Pin Description VREF a VREFb These are the ADC16471’s internal differential reference’s bypass pins Their nominal output voltage is g 1 25V centered around the voltage at the VMID pin typically VA a 2 VREF a VMID and VREFb should be bypassed with a parallel combination of 10 mF and 0 1 mF capacitors For the ADC16071 these are the reference voltage inputs VREF a and VMID should be bypassed with a parallel combination of 10 mF and 0 1 mF capacitors VMID This pin is the internal differential reference’s VA a 2 output pin VMID should be bypassed with a parallel combination of 10 mF and 0 1 mF capacitors VIN a VINb These are the ADC’s differential input pins Signals applied to these pins can be singleended or differential with respect to the VMID voltage PD This is the input pin used to activate the power-down mode When a logic LOW (0) is applied to this pin the supply current drops from 100 mA (max) to 1 3 mA (max) AGND This is the connection to system analog ground Internally this ground is connected to the analog circuitry including the fourthorder modulator DGND This is the connection to system digital ground Internally this ground is connected to all digital circuitry except the modulator’s clock MGND This is the ground pin for the modulator’s clock It should be connected to analog ground through its own connection that is separate from that used by AGND VA a This pin is the connection to the system analog voltage supply Best performance is achieved when this pin is bypassed with a parallel combination of 10 mF and 0 1 mF capacitors VM a This is the modulator’s supply pin VM a should be connected to the system analog voltage supply with a circuit board trace or connection that is separate from that used to supply VA a Best performance is achieved when this pin is bypassed with a parallel combination of 10 mF and 0 1 mF capacitors VD a This pin is the connection to the system digital voltage supply Best performance is achieved when this pin is bypassed with a parallel combination of 10 mF and 0 1 mF capacitors SFMT This is the Serial Format pin The logic level applied to the SFMT pin determines whether conversion data shifted out of the SDO pin is valid on the rising or falling edge of SCO It also controls the format of the Frame Sync Out (FSO) signal See the Serial Interface section for details TM0 TM1 Used to enabled test mode during production Connect both pins to DGND FSI This is the Frame Sync Input pin FSI is an input used to synchronize the ADC16071 ADC16471’s conversions to an external source The state of FSI is sampled on the falling edge of CLK See the Serial Interface section for details CLK This is the clock signal input pin The signal applied to this pin sets the sample rate of the ADC16071 ADC16471’s modulator to fCLK 2 The frequency range can be 1 MHz s fCLK s 25 MHz SCO This is the Serial Clock Output pin The ADC16071 ADC16471’s serial data transmission is synchronous with the SCO signal SCO has a frequency of fCLK 4 See the Serial Interface section for details SDO This is the Serial Data Output pin The ADC16071 ADC16471’s conversion data is shifted out from this pin synchronous to the SCO signal See the Serial Interface section for details 12 Pin Description (Continued) FSO This is the Frame Sync Output pin FSO is used to synchronize an external device to the ADC16071 ADC16471’s 32 SCO cycle data transmission frame The format of the signal on FSO depends on the logic level applied to the SFMT pin See the Serial Interface section for details This is the Time Slot Input pin TSI can be used to allow two ADC16071 ADC16471’s to share a single serial data line The logic level applied to TSI controls the active state of the ADC16071 ADC16471’s DOE pin See the Serial Interface and the Two Channel Multiplexed Operation sections for details This is the Data Output Enable pin DOE is used to control SDO’s TRI-STATE output buffer The active state of DOE is controlled by the logic level applied to the TSI pin See the Serial Interface and the Two Channel Multiplexed Operation sections for details Applications Information TYPICAL PERFORMANCE RESULTS Figure 6 shows a 16k point FFT plot of the baseband output spectrum during conversion of a 24 kHz input signal CLOCK GENERATION The ADC16071 ADC16471 requires a sampling-clock signal that is free of ringing (over undershoot of no more than 100 mVp-p) and has a rise and fall time in the range of 3 ns – 10 ns We have tested and recommended crystal clock oscillators from Ecliptek (EC1100 series) and SaRonix (NCH060 and NCH080 series) Both of these families use HCMOS logic circuitry for very fast rise and fall times TSI DOE TL H 11454 – 13 FIGURE 6 Typical Performance of the ADC16071 ADC16471 at fS e 192 kHz fIN e 24 kHz 13 Applications Information (Continued) Overshoot and ringing can be reduced by adding a series damping resistor between the crystal oscillator’s output (pin 8) and the ADC16071 ADC16471’s CLK (pin 12) as shown in Figure 7 The actual resistor value is dependent on the board layout and trace length that connects the oscillator or CLK source to the ADC A typical starting value is 50X with a range of 27X to 150X Due to the data latency of the ADC16071 ADC16471’s digital filters the first 31 conversions following a frame sync input signal will represent inaccurate data unless the frame syncs are applied at constant 32 SCO cycle intervals If no FSI signal is applied (FSI is kept High or Low) the ADC16071 ADC16471 will internally create a frame sync every 32 SCO cycles The Data Output Enable pin (DOE) is used to enable and disable the output of data on SDO When DOE is deactivated SDO stops driving the serial data line by entering a high impedance TRI-STATE DOE’s active state matches the logic level applied to the Time Slot Input pin (TSI) If a logic Low is applied to TSI the ADC16071 ADC16471’s SDO pin will shift out data when DOE is Low and be in a high impedance TRI-STATE when DOE is High If a logic High is applied to TSI SDO will shift out data when DOE is High and be in a high impedance TRI-STATE when DOE is Low TWO CHANNEL MULTIPLEXED OPERATION Two ADC16071 ADC16471’s can easily be configured to share a single serial data line and operate in a ‘‘stereo’’ or two channel multiplexed mode They share the serial data bus by alternating transmission of conversion data on their respective SDO pins One of the ADC16071 ADC16471’s the Master shifts its conversion data out of SDO during the first 16 SCO cycles of the data transmission frame The other ADC16071 ADC16471 the Slave shifts its data out during the second 16 SCO cycles of the data transmission frame The Slave is selected by applying a logic High to its TSI pin and a logic High to its SFMT pin The Master is chosen by applying a logic Low to its TSI pin and a logic High to its SFMT pin As shown in Figure 8 the Master’s FSO is used to control the DOE of both the Master and the Slave as well as to synchronize the two ADC16071 ADC16471’s by driving the Slave’s Frame Sync Input pin FSI As the Master finishes transmitting its 16 bits of conversion data its FSO goes High This triggers the Slave’s FSI causing the Slave to begin transmitting its 16 bits of conversion data The Master’s DOE is active Low and the Slave’s DOE is active High Since the same signal the Master’s FSO is connected to both of the converters’ DOE pins one converter will shift out data on its SDO pin while the other is in TRI-STATE allowing the two ADC16071 ADC16471’s to share the same serial data transmission line POWER SUPPLY AND GROUNDING The ADC16071 ADC16471 has on-chip 50 pF bypass capacitors between the supply-pin bonding pads and their corresponding grounds There are 24 of these capacitors 6 for the analog section and 18 for the digital resulting in a total value of 1200 pF They help control ringing on the on-chip power supply busses especially in the digital section Further they help enhance the baseband noise performance of the analog modulator TL H 11454–23 FIGURE 7 Damping Resistor Reduces Clock Signal Overshoot SERIAL INTERFACE The ADC16071 and the ADC16471 have three serial interface output pins Serial Data Output (SDO) Frame Sync Output (FSO) and Serial Clock Output (SCO) SCO has a frequency of fCLK 4 Each of the ADC16071 ADC16471’s 16-bit conversions is transmitted within the first half of the data transmission frame A data transmission frame is 32 SCO cycles in duration Two’s complement data shifts out on the SDO pin beginning with bit 15 (MSB) and ending with bit 0 (LSB) taking 16 SCO cycles SDO then shifts out zeroes for the next 16 SCO cycles to maintain compatibility with two channel multiplexed operation The serial data that is shifted out of the SDO pin is synchronous with SCO Depending on the logic level applied to the Serial Format pin (SFMT) the data on the SDO pin is valid on either the falling or rising edge of SCO If a logic Low is applied to SFMT then the data on SDO is valid on the falling edge of SCO If a logic High is applied to SFMT then the data on SDO is valid on the rising edge of SCO See Figure 2 The FSO signal is used to synchronize other devices to the ADC16071 ADC16471’s data transmission frame Depending on the logic level applied to SFMT the signal on FSO is either a short pulse (approximately one SCO cycle in duration) ending just before the transmission of bit 15 on SDO or a square wave with a period of 32 SCO cycles going low just before the transmission of bit 15 and going high just after the transmission of bit 0 If a logic Low is applied to SFMT FSO will be high for approximately one SCO cycle and fall low just before the transmission of bit 15 and stay low for the remainder of the transmission frame If a logic High is applied to SFMT FSO will be low during the transmission of bits 15 –0 and high during the next 16 SCO cycles See Figure 3 The Frame Sync Input (FSI) is used to synchronize the ADC16071 ADC16471’s conversions to an external source The logic state of FSI is captured by the ADC16071 ADC16471 on the falling edge of CLK If an FSI low to high transition is sensed between adjacent CLK falling edges the ADC16071 ADC16471 will interrupt its current data transmission frame and begin a new one See Figure 4 14 Applications Information (Continued) TL H 11454 – 14 FIGURE 8 Two Channel Multiplexed Operation Connection Diagram Best converter performance is achieved when these internal bypass capacitors are supplemented with additional external power-supply decoupling capacitors This ensures the lowest ac-bypass impedance path for the ADC16071 ADC16471’s dynamic current requirements Each of the ADC16071 ADC16471’s four supply pins should be individually bypassed using a parallel combination of 10 mF (tantalum) and 0 1 mF (monolithic ceramic) to its corresponding ground pin VA a (Pin 21) x AGND (Pin 4) VM a (Pin 20) x MGND (Pin 5) VD a (Pin 19) x DGND (Pin 6) VD a (Pin 18) x DGND (Pin 7) Short lead lengths are mandatory Therefore surface mount capacitors are strongly recommended POWER SUPPLY VOLTAGES FOR BEST PERFORMANCE While adequate performance will be achieved by operating the ADC16071 ADC16471 with a 5V connected to VA a VM a and VD a dynamic performance as measured by S (N a D) can be further enhanced by slightly raising the analog supply voltage and lowering the digital supply voltage ANALOG INPUT The ADC16071 and the ADC16471 generate a two’s complement output determined by the following equation (VIN a b VINb) (32768) (VREF a b VREFb) Round off to the nearest integer value between b32768 and 32767 The signals applied to VIN a and VINb must be between VA a and analog ground For accurate conversions the absolute difference between VIN a and VINb should be less than the difference between VREF a and VREFb Best harmonic performance will result when a differential voltage is applied to VIN a and VINb that has a common mode voltage at or below VMID Output Code e Due to overloading in the ADC16071 ADC16471’s DR modulator performance degrades considerably as the input amplitude approaches full scale With an input that peaks at b 2 dB from full scale S (N a D) is about 2 dB worse than with a b6 dB input With a b1 dB input S (N a D) can be 10 dB worse than with a b6 dB input 15 Applications Information (Continued) ANALOG SIGNAL CONDITIONING The ADC16071 ADC16471’s digital comb and FIR filter combine to create the band-limiting anti-aliasing filter generating a steep cutoff at the upper range of the sampled baseband Additional external filtering is needed to ensure that the best conversion performance is maintained The external filtering uses a simple R-C lowpass filter A suggested circuit is shown in Figure 9 The values of R1 R2 C1 C2 and C3 are found using the following equation 1 f c ( b 3 dB) e 6qRC where R e R1 e R2 and C e C1 e C2 e C3 The effects of the external filter are minimized by choosing a minimum cutoff frequency equal to fCLK 32 As an example for fCLK equal to 6 144 MHz set R1 e R2 e 82 5X and C1 e C2 e C3 e 3300 pF This sets the input network’s cutoff frequency at 194 kHz For fCLK equal to 24 576 MHz set R1 e R2 e 20X and C1 e C2 e C3 e 3300 pF This sets the input network’s cutoff frequency at 803 kHz RELATION BETWEEN CAPACITOR DIELECTRIC AND SIGNAL DISTORTION For any capacitors connected to the ADC16071 ADC16471’s analog inputs the dielectric plays an important role in determining the amount of distortion generated in the input signal The capacitors used must have low dielectric absorption This requirement is fulfilled using capacitors that have film dielectrics Of these polypropylene and polystyrene are the best These are followed by polycarbonate and mylar If ceramic capacitors are chosen use only capacitors with NPO dielectrics INTERNAL DIFFERENTIAL BANDGAP REFERENCE A fully differential bandgap reference generates local feedback voltages VREF a and VREFb for the analog modulator The outputs of this reference are trimmed to be equal to VMID plus or minus 1 25V This gives a differential reference voltage of 2 5V which results in a g 2 5V differential input range The ADC16071 does not have the internal differential bandgap reference allowing the user the flexibility to determine the full scale range by using an external voltage reference EXTERNAL VOLTAGE REFERENCE FOR THE ADC16071 Figure 10 shows the suggested connection diagram for the ADC16071 The LM4041-ADJ is set to 2 0V and is applied to the ADC16071’s VREF a input The reference voltage must be free of noise This is accomplished using the same capacitor combination used with the ADC16471’s reference pins with the exception of VREFb which is connected to analog ground Figures 11 and 12 show the suggested circuits for ac-coupled applications Suggested values R1 e R2 e 20X 5% metal film C1 e C2 e C3 e 3300 pF 5% polypropylene TL H 11454 – 15 Parallel combination of 10 mF tantalum and a 0 1 mF monolithic ceramic capacitors FIGURE 9 Typical Connection Diagram for the ADC16471 16 Applications Information (Continued) Suggested values R1 e R2 e 20X 5% metal film C1 e C2 e C3 e 3300 pF 5% polypropylene Parallel combination of 10 mF tantalum and a 0 1 mF monolithic ceramic capacitors TL H 11454 – 16 FIGURE 10 Typical Connection Diagram for the ADC16071 Suggested values R1 e R2 e 20X 5% metal film C1 e C2 e C3 e 3300 pF 5% polypropylene Parallel combination of 10 mF tantalum and a 0 1 mF monolithic ceramic capacitors TL H 11454 – 17 FIGURE 11 Typical Connection Diagram for the ADC16471 with AC-Coupled Inputs Suggested values R1 e R2 e 20X 5% metal film C1 e C2 e C3 e 3300 pF 5% polypropylene Parallel combination of 10 mF tantalum and a 0 1 mF monolithic ceramic capacitors TL H 11454 – 18 FIGURE 12 Typical Connection Diagram for the ADC16071 with AC-Coupled Inputs 17 Applications Information (Continued) DSP INTERFACES The ADC16071 ADC16471 was designed to connect to popular DSPs without intervening ‘‘glue logic’’ Figures 13 14 and 15 show suggested connection schematics for the DSP56001 TMS320C3x and the ADSP-2101 families TL H 11454 – 19 FIGURE 13 Interface Connections between the ADC16071 ADC16471 and the Motorola DSP56001 TL H 11454 – 20 FIGURE 14 Interface Connections between the ADC16071 ADC16471 and the Texas Instruments TMS320C3x TL H 11454 – 21 FIGURE 15 Interface Connections between the ADC16071 ADC16471 and the Analog Devices ADSP-2101 18 Physical Dimensions inches (millimeters) 24-Lead (0 300 Wide) Molded Small Outline Package JEDEC Order Number ADC16071CIWM or ADC16471CIWM NS Package Number M24B 19 ADC16071 ADC16471 16-Bit Delta-Sigma 192 ks s Analog-to-Digital Converters Physical Dimensions inches (millimeters) (Continued) 24-Lead (0 300 Wide) Molded Dual-In-Line Package Order Number ADC16071CIN or ADC16471CIN NS Package Number N24C LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which (a) are intended for surgical implant into the body or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user National Semiconductor Corporation 2900 Semiconductor Drive P O Box 58090 Santa Clara CA 95052-8090 Tel 1(800) 272-9959 TWX (910) 339-9240 National Semiconductor GmbH Livry-Gargan-Str 10 D-82256 F4urstenfeldbruck Germany Tel (81-41) 35-0 Telex 527649 Fax (81-41) 35-1 National Semiconductor Japan Ltd Sumitomo Chemical Engineering Center Bldg 7F 1-7-1 Nakase Mihama-Ku Chiba-City Ciba Prefecture 261 Tel (043) 299-2300 Fax (043) 299-2500 2 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor Hong Kong Ltd 13th Floor Straight Block Ocean Centre 5 Canton Rd Tsimshatsui Kowloon Hong Kong Tel (852) 2737-1600 Fax (852) 2736-9960 National Semiconductores Do Brazil Ltda Rue Deputado Lacorda Franco 120-3A Sao Paulo-SP Brazil 05418-000 Tel (55-11) 212-5066 Telex 391-1131931 NSBR BR Fax (55-11) 212-1181 National Semiconductor (Australia) Pty Ltd Building 16 Business Park Drive Monash Business Park Nottinghill Melbourne Victoria 3168 Australia Tel (3) 558-9999 Fax (3) 558-9998 National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications