ADS8411 SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 16-BIT, 2 MSPS, UNIPOLAR INPUT, MICRO POWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE FEATURES APPLICATIONS • • • • • • • • • • • • • • • 2-MHz Sample Rate 16-Bit NMC Ensured Over Temperature Zero Latency Unipolar Single-Ended Input Range: 0 V to Vref Onboard Reference Onboard Reference Buffer High-Speed Parallel Interface Power Dissipation: 175 mW at 2 MHz Typ Wide Digital Supply 8-/16-Bit Bus Transfer 48-Pin TQFP Package ESD Sensitive – HBM Capability of 500 V, 1000 V at All Input Pins • • • DWDM Instrumentation High-Speed, High-Resolution, Zero Latency Data Acquisition Systems Transducer Interface Medical Instruments Communication DESCRIPTION The ADS8411 is a 16-bit, 2 MHz A/D converter with an internal 4.096-V reference. The device includes a 16-bit capacitor-based SAR A/D converter with inherent sample and hold. The ADS8411 offers a full 16-bit interface and an 8-bit option where data is read using two 8-bit read cycles. The ADS8411 has a unipolar single-ended input. It is available in a 48-lead TQFP package and is characterized over the industrial -40°C to 85°C temperature range. SAR +IN −IN + _ Output Latches and 3-State Drivers CDAC BYTE 16-/8-Bit Parallel DATA Output Bus Comparator RESET REFIN REFOUT 4.096-V Internal Reference Clock Conversion and Control Logic CONVST BUSY CS RD 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. 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 © 2002–2004, Texas Instruments Incorporated ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 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 (1) MODEL ADS8411I ADS8411IB (1) MAXIMUM INTEGRAL LINEARITY (LSB) –6 ~ 6 –2.5 ~ 2.5 MAXIMUM DIFFERENTIAL LINEARITY (LSB) NO MISSING CODES RESOLUTION (BIT) PACKAGE TYPE 15 48 Pin TQFP –2~3 –1~2 16 48 Pin TQFP PACKAGE DESIGNATOR PFB PFB TEMPERATURE RANGE ORDERING INFORMATION TRANSPORT MEDIA QUANTITY ADS8411IPFBT Tape and reel 250 ADS8411IPFBR Tape and reel 1000 ADS8411IBPFBT Tape and reel 250 ADS8411IBPFBR Tape and reel 1000 –40°C to 85°C –40°C to 85°C For the most current specifications and package information, refer to our website at www.ti.com. ABSOLUTE MAXIMUM RATINGS over operating free-air temperature range unless otherwise noted (1) UNIT Voltage Voltage range +IN to AGND –0.4 V to +VA + 0.1 V –IN to AGND –0.4 V to 0.5 V +VA to AGND –0.3 V to 7 V +VBD to BDGND +VA to +VBD –0.3 V to 7 V –0.3 V to 2.55 V Digital input voltage to BDGND –0.3 V to +VBD + 0.3 V Digital output voltage to BDGND –0.3 V to +VBD + 0.3 V TA Operating free-air temperature range –40°C to 85°C Tstg Storage temperature range –65°C to 150°C Junction temperature (TJ max) TQFP package Power dissipation θJA thermal impedance Lead temperature, soldering (1) 2 150°C (TJMax - TA)/θJA 86°C/W Vapor phase (60 sec) 215°C Infrared (15 sec) 220°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 under recommended operating conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 SPECIFICATIONS TA = –40°C to 85°C, +VA = 5 V, +VBD = 3 V or 5 V, Vref = 4.096 V, fSAMPLE = 2 MHz (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT ANALOG INPUT Full-scale input voltage (1) +IN – (–IN) Absolute input voltage 0 Vref +IN –0.2 Vref + 0.2 –IN –0.2 0.2 V V Input capacitance 25 pF Input leakage current 0.5 nA 16 Bits SYSTEM PERFORMANCE Resolution No missing codes Integral linearity DNL Differential linearity EO Offset error (4) 16 ADS8411IB –6 ±4 6 –2.5 ±1.5 2.5 LSB –2 ±1 3 ADS8411IB –1 ±0.8 2 –1.5 ±0.5 1.5 mV ADS8411IB –0.75 ±0.25 0.75 mV ADS8411I –0.15 0.15 –0.098 0.098 ADS8411IB Noise PSRR Bits ADS8411I ADS8411I Gain error (4) (5) EG 15 ADS8411IB ADS8411I (2) (3) INL ADS8411I DC Power supply rejection ratio At FFFFh output code, +VA = 4.75 V to 5.25 V, Vref = 4.096 V (4) LSB %FS 60 µV RMS 2 LSB SAMPLING DYNAMICS Conversion time 340 Acquisition time 100 400 ns ns Throughput rate 2 MHz Aperture delay 2 ns Aperture jitter 25 ps Step response 100 ns Overvoltage recovery 100 ns VIN = 4 Vpp at 100 kHz –90 dB DYNAMIC CHARACTERISTICS (6) THD Total harmonic distortion VIN = 4 Vpp at 500 kHz –88.5 dB SNR Signal-to-noise ratio VIN = 4 Vpp at 100 kHz 86 dB SINAD Signal-to-noise + distortion VIN = 4 Vpp at 100 kHz 85 dB SFDR Spurious free dynamic range VIN = 4 Vpp at 100 kHz 90 dB VIN = 4 Vpp at 500 kHz 88 dB 5 MHz -3dB Small signal bandwidth EXTERNAL VOLTAGE REFERENCE INPUT Reference voltage at REFIN, Vref Reference resistance (1) (2) (3) (4) (5) (6) (7) (7) 3.9 4.096 500 4.2 V kΩ Ideal input span, does not include gain or offset error. LSB means least significant bit This is endpoint INL, not best fit. Measured relative to an ideal full-scale input [+IN – (–IN)] of 4.096 V This specification does not include the internal reference voltage error and drift. Calculated on the first nine harmonics of the input frequency Can vary ±20% 3 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 SPECIFICATIONS (continued) TA = –40°C to 85°C, +VA = 5 V, +VBD = 3 V or 5 V, Vref = 4.096 V, fSAMPLE = 2 MHz (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 120 ms INTERNAL REFERENCE OUTPUT Vref Internal reference start-up time From 95% (+VA), with 1 µF storage capacitor Reference voltage IOUT = 0 Source current Static load Line regulation +VA = 4.75 ~ 5.25 V 0.6 mV Drift IOUT = 0 36 PPM/°C 4.065 4.096 4.13 V 10 µA DIGITAL INPUT/OUTPUT Logic family — CMOS VIH High level input voltage IIH = 5 µA +VBD – 1 VIL Low level input voltage IIL = 5 µA –0.3 +VBD + 0.3 0.8 VOH High level output voltage IOH = 2 TTL loads +VBD – 0.6 +VBD VOL Low level output voltage IOL = 2 TTL loads 0 0.4 V Data format — straight binary POWER SUPPLY REQUIREMENTS Power supply voltage PD +VBD 2.7 +VA 4.75 3 5.25 V 5 5.25 +VA Supply current (8) fs = 2 MHz 35 38 mA V Power dissipation (8) fs = 2 MHz 175 190 mW 85 °C TEMPERATURE RANGE TA (8) 4 Operating free-air –40 This includes only +VA current. +VBD current is typically 1 mA with 5-pF load capacitance on output pins. ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TIMING CHARACTERISTICS All specifications typical at –40°C to 85°C, +VA = +VBD = 5 V (1) (2) (3) PARAMETER MIN tCONV Conversion time 340 tACQ Acquisition time 100 tpd1 CONVST low to BUSY high tpd2 Propagation delay time, end of conversion to BUSY low tw1 Pulse duration, CONVST low tsu1 Setup time, CS low to CONVST low tw2 Pulse duration, CONVST high TYP MAX UNIT 400 ns ns 30 ns 5 ns 20 ns 0 ns 20 ns CONVST falling edge jitter 10 tw3 Pulse duration, BUSY signal low tw4 Pulse duration, BUSY signal high th1 Hold time, first data bus data transition (RD low, or CS low for read cycle, or BYTE input changes) after CONVST low td1 tsu2 tw5 Pulse duration, RD low ten Enable time, RD low (or CS low for read cycle) to data valid td2 Delay time, data hold from RD high 0 td3 Delay time, BYTE rising edge or falling edge to data valid 2 tw6 Pulse duration, RD high 20 ns tw7 Pulse duration, CS high 20 ns th2 Hold time, last RD (or CS for read cycle ) rising edge to CONVST falling edge 50 ns tsu3 Setup time, BYTE transition to RD falling edge 0 ns th3 Hold time, BYTE transition to RD falling edge 0 tdis Disable time, RD high (CS high for read cycle) to 3-stated data bus 20 ns td5 Delay time, end of conversion to MSB data valid 10 ns tsu4 Byte transition setup time, from BYTE transition to next BYTE transition 50 ns td6 Delay time, CS rising edge to BUSY falling edge 50 ns td7 Delay time, BUSY falling edge to CS rising edge 50 ns tsu(AB) Setup time, from the falling edge of CONVST (used to start the valid conversion) to the next falling edge of CONVST (when CS = 0 and CONVST used to abort) or to the next falling edge of CS (when CS is used to abort) 60 tsu5 Setup time, falling edge of CONVST to read valid data (MSB) from current conversion th4 Hold time, data (MSB) from previous conversion hold valid from falling edge of CONVST (1) (2) (3) Min(tACQ) ps ns 370 ns 40 ns Delay time, CS low to RD low (or BUSY low to RD low) 0 ns Setup time, RD high to CS high 0 ns 50 ns 20 ns ns 20 ns ns 340 MAX(tCONV) + MAX(td5) ns ns MIN(tCONV) ns All input signals are specified with tr = tf = 5 ns (10% to 90% of +VBD) and timed from a voltage level of (VIL + VIH)/2. See timing diagrams. All timings are measured with 20 pF equivalent loads on all data bits and BUSY pins. 5 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TIMING CHARACTERISTICS All specifications typical at –40°C to 85°C, +VA = 5 V, +VBD = 3 V (1) (2) (3) PARAMETER MIN TYP MAX UNIT 400 ns tCONV Conversion time 340 tACQ Acquisition time 100 tpd1 CONVST low to conversion started (BUSY high) 40 ns tpd2 Propagation delay time, end of conversion to BUSY low 10 ns tw1 Pulse duration, CONVST low tsu1 Setup time, CS low to CONVST low tw2 Pulse duration, CONVST high ns 20 ns 0 ns 20 ns CONVST falling edge jitter 10 tw3 Pulse duration, BUSY signal low tw4 Pulse duration, BUSY signal high th1 Hold time, first data bus transition (RD low, or CS low for read cycle, or BYTE input changes) after CONVST low td1 tsu2 tw5 Pulse duration, RD low ten Enable time, RD low (or CS low for read cycle) to data valid td2 Delay time, data hold from RD high 0 td3 Delay time, BYTE rising edge or falling edge to data valid 2 tw6 Pulse duration, RD high 20 ns tw7 Pulse duration, CS high 20 ns th2 Hold time, last RD (or CS for read cycle ) rising edge to CONVST falling edge 50 ns tsu3 Setup time, BYTE transition to RD falling edge 0 ns th3 Hold time, BYTE transition to RD falling edge 0 tdis Disable time, RD high (CS high for read cycle) to 3-stated data bus 30 ns td5 Delay time, end of conversion to MSB data valid 20 ns tsu4 Byte transition setup time, from BYTE transition to next BYTE transition 50 ns td6 Delay time, CS rising edge to BUSY falling edge 50 ns td7 Delay time, BUSY falling edge to CS rising edge 50 ns tsu(AB) Setup time, from the falling edge of CONVST (used to start the valid conversion) to the next falling edge of CONVST (when CS = 0 and CONVST used to abort) or to the next falling edge of CS (when CS is used to abort) 70 tsu5 Setup time, falling edge of CONVST to read valid data (MSB) from current conversion th4 Hold time, data (MSB) from previous conversion hold valid from falling edge of CONVST (1) (2) (3) 6 Min(tACQ) ps ns 370 ns 40 ns Delay time, CS low to RD low (or BUSY low to RD low) 0 ns Setup time, RD high to CS high 0 ns 50 ns 30 ns ns 30 ns ns 350 MAX(tCONV) + MAX(td5) ns ns MIN(tCONV) All input signals are specified with tr = tf = 5 ns (10% to 90% of +VBD) and timed from a voltage level of (VIL + VIH)/2. See timing diagrams. All timings are measured with 20 pF equivalent loads on all data bits and BUSY pins. ns ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 PIN ASSIGNMENTS BUSY BDGND +VBD DB0 DB1 DB2 DB3 DB4 DB5 DB6 DB7 BDGND PFB PACKAGE (TOP VIEW) 36 35 34 33 32 31 30 29 28 27 26 25 37 24 38 23 39 22 40 21 41 20 42 19 43 18 44 17 45 16 46 15 47 14 48 3 4 5 6 7 8 13 9 10 11 12 REFIN REFOUT NC +VA AGND +IN -IN AGND +VA +VA 1 2 +VBD DB8 DB9 DB10 DB11 DB12 DB13 DB14 DB15 AGND AGND +VA AGND AGND +VBD RESET BYTE CONVST RD CS +VA AGND AGND +VA REFM REFM NC - No connection 7 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 Terminal Functions NAME NO. I/O AGND 5, 8, 11, 12, 14, 15, 44, 45 – Analog ground BDGND DESCRIPTION 25, 35 – Digital ground for bus interface digital supply BUSY 36 O Status output. High when a conversion is in progress. BYTE 39 I Byte select input. Used for 8-bit bus reading. 0: No fold back 1: Low byte D[7:0] of the 16 most significant bits is folded back to high byte of the 16 most significant pins DB[15:8]. CONVST 40 I Convert start. The falling edge of this input ends the acquisition period and starts the hold period. CS 42 I Chip select. The falling edge of this input starts the acquisition period. 8-Bit Bus Data Bus 16-Bit Bus BYTE = 0 BYTE = 1 BYTE = 0 DB15 16 O D15 (MSB) D7 D15 (MSB) DB14 17 O D14 D6 D14 DB13 18 O D13 D5 D13 DB12 19 O D12 D4 D12 DB11 20 O D11 D3 D11 DB10 21 O D10 D2 D10 DB9 22 O D9 D1 D9 DB8 23 O D8 D0 (LSB) D8 DB7 26 O D7 All ones D7 DB6 27 O D6 All ones D6 DB5 28 O D5 All ones D5 DB4 29 O D4 All ones D4 DB3 30 O D3 All ones D3 DB2 31 O D2 All ones D2 DB1 32 O D1 All ones D1 DB0 33 O D0 (LSB) All ones D0 (LSB) –IN 7 I Inverting input channel +IN 6 I Non inverting input channel NC 3 – No connection REFIN 1 I Reference input REFM 47, 48 I Reference ground REFOUT 2 O Reference output. Add 1 µF capacitor between the REFOUT pin and REFM pin when internal reference is used. RESET 38 I Current conversion is aborted and output latches are cleared (set to zeros) when this pin is asserted low. RESET works independantly of CS. RD 41 I Synchronization pulse for the parallel output. When CS is low, this serves as the output enable and puts the previous conversion result on the bus. +VA 4, 9, 10, 13, 43, 46 – Analog power supplies, 5-V dc 24, 34, 37 – Digital power supply for bus +VBD 8 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TIMING DIAGRAMS tw2 tw1 CONVST (used in normal conversion) tcycle CONVST (used in ABORT) tsu(AB) tpd1 tsu(AB) tpd2 tw4 tpd1 tw3 BUSY tsu1 tw7 td7 CS td6 CONVERT† tCONV tCONV SAMPLING† (When CS Toggle) tACQ BYTE tsu4 th1 tsu2 td1 th2 RD Data to be read† Invalid Previous Conversion th4 tdis ten tsu5 DB[15:8] Invalid Current Conversion Hi−Z Hi−Z D [15:8] DB[7:0] Hi−Z D [7:0] Hi−Z D [7:0] †Signal internal to device Figure 1. Timing for Conversion and Acquisition Cycles With CS and RD Toggling 9 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TIMING DIAGRAMS (continued) tw1 CONVST (used in normal conversion) tw2 tcycle CONVST (used in ABORT) tsu(AB) tpd1 tsu(AB) tpd2 tw4 tw3 BUSY tw7 tsu1 td7 CS td6 CONVERT† tCONV tCONV SAMPLING† (When CS Toggle) tACQ BYTE th1 RD = 0 Data to be read† tdis ten DB[15:8] DB[7:0] †Signal Invalid Current Conversion tsu5 Hi−Z Previous D [15:8] Hi−Z Hi−Z Previous D [7:0] Hi−Z internal to device tdis Invalid Previous Conversion th4 tsu4 th2 ten D [15:8] D [7:0] D [7:0] Hi−Z Repeated D [15:8] Hi−Z Repeated D [7:0] ten Figure 2. Timing for Conversion and Acquisition Cycles With CS Toggling, RD Tied to BDGND 10 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TIMING DIAGRAMS (continued) tw1 tw2 CONVST (used in normal conversion) tcycle CONVST (used in ABORT) tsu(AB) tpd1 tsu(AB) tpd2 tw4 tpd1 tw3 BUSY CS = 0 CONVERT† tCONV tCONV t(ACQ) SAMPLING† (When CS = 0) BYTE tsu4 th1 th2 RD tdis ten Data to be read† th4 DB[15:8] DB[7:0] †Signal Invalid Invalid Previous Conversion Current Conversion tsu5 Hi−Z Hi−Z D [15:8] D [7:0] D [7:0] Hi−Z Hi−Z internal to device Figure 3. Timing for Conversion and Acquisition Cycles With CS Tied to BDGND, RD Toggling 11 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TIMING DIAGRAMS (continued) tw1 CONVST (used in normal conversion) tw2 tcycle CONVST (used in ABORT) tsu(AB) tpd1 tsu(AB) tpd2 tw4 tpd1 tpd2 tw3 BUSY CS = 0 CONVERT† tCONV tCONV tACQ SAMPLING† (When CS Toggle) th1 th1 BYTE RD = 0 td3 td3 td5 th4 tsu5 Previous MSB Invalid DB[15:8] Previous Previous LSB LSB Invalid DB[7:0] †Signal td5 th4 td3 tsu5 Invalid MSB LSB MSB MSB LSB MSB Invalid internal to device Figure 4. Timing for Conversion and Acquisition Cycles With CS and RD Tied to BDGND—Auto Read CS RD tsu4 BYTE ten tdis tdis ten DB[15:0] td3 Hi−Z Valid Hi−Z Valid Valid Figure 5. Detailed Timing for Read Cycles 12 Hi−Z ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TYPICAL CHARACTERISTICS At –40°C to 85°C, +VA = 5 V, +VBD = 5 V, REFIN = 4.096 V (internal reference used) and fsample = 2 MHz (unless otherwise noted) HISTOGRAM (DC CODE SPREAD) vs FULL SCALE 131071 CONVERSIONS SIGNAL-TO-NOISE RATIO vs FREE-AIR TEMPERATURE 70000 86.8 +VA = 5 V, +VBD = 3.3 V Code = 65235 86.6 SNR − Signal-to-Noise Ratio − dB 60000 50000 40000 30000 20000 10000 86.4 86.2 86 85.8 85.6 85.4 85.2 −40 65239 65235 65230 0 0 20 40 60 TA − Free-Air Temperature − °C Figure 7. SIGNAL-TO-NOISE AND DISTORTION vs FREE-AIR TEMPERATURE EFFECTIVE NUMBER OF BITS vs FREE-AIR TEMPERATURE 80 13.6 83.4 83.2 83 ENOB − Effective Number of Bits − Bits fi = 100 kHz, +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 83.6 82.8 82.6 82.4 82.2 82 81.8 81.6 −40 −20 Figure 6. 83.8 SINAD − Signal-to-Nois and Distortion − dB fi = 100 kHz, +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference −20 0 20 40 60 TA − Free-Air Temperature − °C Figure 8. 80 fi = 100 kHz, +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 13.55 13.5 13.45 13.4 13.35 13.3 13.25 −40 −20 0 20 40 60 TA − Free-Air Temperature − °C 80 Figure 9. 13 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TYPICAL CHARACTERISTICS (continued) SPURIOUS FREE DYNAMIC RANGE vs FREE-AIR TEMPERATURE TOTAL HARMONIC DISTORTION vs FREE-AIR TEMPERATURE −91 fi = 100 kHz, +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 95 94.5 THD − Total Harmonic Distortion − dB SFDR − Spurious Free Dynamic Range − dB 95.5 94 93.5 93 92.5 92 −40 −20 0 20 40 60 TA − Free-Air Temperature − °C −92.5 −93 −93.5 −94 −20 0 20 40 60 80 TA − Free-Air Temperature − °C Figure 10. Figure 11. SIGNAL-TO-NOISE RATIO vs INPUT FREQUENCY EFFECTIVE NUMBER OF BITS vs INPUT FREQUENCY 13.9 86.7 ENOB − Effective Number of Bits − Bits +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 86.8 SNR − Signal-to-Noise Ratio − dB −92 −94.5 −40 80 86.9 86.6 86.5 86.4 86.3 86.2 86.1 86 0 20 40 60 80 fi − Input Frequency − kHz Figure 12. 14 −91.5 fi = 100 kHz, +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 100 +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 13.85 13.8 13.75 13.7 13.65 13.6 13.55 13.5 13.45 13.4 0 20 40 60 80 fi − Input Frequency − kHz Figure 13. 100 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TYPICAL CHARACTERISTICS (continued) SIGNAL-TO-NOISE AND DISTORTION vs INPUT FREQUENCY SPURIOUS FREE DYNAMIC RANGE vs INPUT FREQUENCY 103 +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 85 SFDR − Spurious Free Dynamic Range − dB SINAD − Signal-to-Nois and Distortion − dB 85.50 84.50 84 83.50 83 82.50 0 20 40 60 80 101 100 99 98 97 96 95 94 100 +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 102 0 20 fi − Input Frequency − kHz Figure 14. Figure 15. TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY SUPPLY CURRENT vs SAMPLE RATE −94 100 33.5 +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 33 ICC − Supply Current − mA THD − Total Harmonic Distortion − dB −92 −93 40 60 80 fi − Input Frequency − kHz −95 −96 −97 −98 −99 32.5 32 +VA = 5 V, +VBD = 3.3 V, TA = 25°C, Internal Reference 31.5 31 30.5 30 29.5 −100 29 −101 0 20 40 60 80 fi − Input Frequency − kHz Figure 16. 100 28.5 500 700 900 1100 1300 1500 1700 1900 Samply Rate − KSPS Figure 17. 15 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TYPICAL CHARACTERISTICS (continued) GAIN ERROR vs SUPPLY VOLTAGE OFFSET ERROR vs SUPPLY VOLTAGE 0.45 0.25 +VBD = 3.3 V, TA = 25°C, External Reference 0.35 EO − Offset Error − mV E G − Gain Error − mV 0.20 +VB D= 3.3 V, TA = 25°C, External Reference 0.40 0.15 0.10 0.30 0.25 0.20 0.15 0.10 0.05 0.05 0 4.75 4.85 4.95 5.05 5.15 VDD − Supply Voltage − V 0 4.75 5.25 Figure 18. Figure 19. INTERNAL VOLTAGE REFERENCE vs FREE-AIR TEMPERATURE GAIN ERROR vs FREE-AIR TEMPERATURE +VA = 5 V, +VBD = 3.3 V 5.25 +VA = 5 V, +VBD = 3.3 V, External Reference 0.30 0.25 4.090 E G − Gain Error − mV Internal Voltage Reference − V 4.091 4.089 4.088 4.087 4.086 0.20 0.15 0.10 0.05 0 4.085 −0.05 4.084 −0.10 −20 0 20 40 60 TA − Free-Air Temperature − °C Figure 20. 16 5.15 0.35 4.092 4.083 −40 4.85 4.95 5.05 VDD − Supply Voltage − V 80 −0.15 −40 −20 0 20 40 60 TA − Free-Air Temperature − °C Figure 21. 80 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TYPICAL CHARACTERISTICS (continued) OFFSET ERROR vs FREE-AIR TEMPERATURE 0.5 33.6 +VA = 5 V, +VBD = 3.3 V, External Reference 0.3 0.2 0.1 0 −0.1 33 32.8 32.6 32.4 −0.3 32.2 −20 0 20 40 60 TA − Free-Air Temperature − °C 32 −40 80 Figure 23. DIFFERENTIAL NONLINEARITY vs FREE-AIR TEMPERATURE INTEGRAL NONLINEARITY vs FREE-AIR TEMPERATURE INL − Integral Nonlinearity − LSBs Max 1 0 80 2.5 1.5 0.5 −20 0 20 40 60 TA − Free-Air Temperature − °C Figure 22. 2 DNL − Differential Nonlinearity − LSBs 33.2 −0.2 −0.4 −40 +VA = 5 V, +VBD = 3.3 V 33.4 ICC − Supply Current − mA 0.4 EO − Offset Error − mV SUPPLY CURRENT vs FREE-AIR TEMPERATURE +VA = 5 V, +VBD = 3.3 V, Internal Reference −0.5 Min −1 2 1.5 MAX 1 0.5 0 −0.5 MIN −1 −1.5 −2 −1.5 −40 −20 0 20 40 60 TA − Free-Air Temperature − °C Figure 24. 80 −2.5 −40 −25 −10 5 20 35 50 65 80 TA − Free-Air Temperature − °C Figure 25. 17 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 TYPICAL CHARACTERISTICS (continued) DNL 4 3 DNL − LSBs 2 1 0 −1 −2 −3 −4 0 32768 Code Figure 26. 16384 49152 65536 49152 65536 INL 4 3 INL − LSBs 2 1 0 −1 −2 −3 −4 0 32768 Code Figure 27. 16384 FFT Magnitude − dB 0 −20 −40 −60 −80 −100 −120 −140 −160 −180 0 100 200 300 400 500 600 Frequency − kHz Figure 28. 18 700 800 900 1000 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 APPLICATION INFORMATION MICROCONTROLLER INTERFACING ADS8411 to 8-Bit Microcontroller Interface Figure 29 shows a parallel interface between the ADS8411 and a typical microcontroller using the 8-bit data bus. The BUSY signal is used as a falling-edge interrupt to the microcontroller. Analog 5 V 0.1 µF AGND 10 µF Ext Ref Input 0.1 µF 1 µF Micro Controller -IN REFM AGND +IN +VA REFIN Analog Input Digital 3 V ADS8411 GPIO CS GPIO P[7:0] BYTE DB[15:8] RD CONVST BUSY RD GPIO INT 0.1 µF BDGND BDGND +VBD Figure 29. ADS8411 Application Circuitry (using external reference) Analog 5 V 0.1 µF AGND 10 µF 0.1 µF AGND AGND REFM REFIN REFOUT +VA 1 µF ADS8411 Figure 30. Use Internal Reference PRINCIPLES OF OPERATION The ADS8411 is a high-speed successive approximation register (SAR) analog-to-digital converter (ADC). The architecture is based on charge redistribution, which inherently includes a sample/hold function. See Figure 29 for the application circuit for the ADS8411. The conversion clock is generated internally. The conversion time of 400 ns is capable of sustaining a 2-MHz throughput. 19 ADS8411 SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 www.ti.com PRINCIPLES OF OPERATION (continued) The analog input is provided to two input pins: +IN and –IN. When a conversion is initiated, the differential input on these pins is sampled on the internal capacitor array. While a conversion is in progress, both inputs are disconnected from any internal function. REFERENCE The ADS8411 can operate with an external reference with a range from 3.9 V to 4.2 V. A 4.096-V internal reference is included. When the internal reference is used, pin 2 (REFOUT) should be connected to pin 1 (REFIN) with 0.1-µF decoupling capacitor and 1-µF storage capacitor between pin 2 (REFOUT) and pins 47 and 48 (REFM) (see Figure 30). The internal reference of the converter is double buffered. If an external reference is used, the second buffer provides isolation between the external reference and the CDAC. This buffer is also used to recharge all of the capacitors of the CDAC during conversion. Pin 2 (REFOUT) can be left unconnected (floating) if an external reference is used. ANALOG INPUT When the converter enters the hold mode, the voltage difference between the +IN and -IN inputs is captured on the internal capacitor array. The voltage on the –IN input is limited between –0.2 V and 0.2 V, allowing the input to reject small signals which are common to both the +IN and –IN inputs. The +IN input has a range of –0.2 V to Vref + 0.2 V. The input span (+IN – (–IN)) is limited to 0 V to Vref. The input current on the analog inputs depends upon a number of factors: sample rate, input voltage, and source impedance. Essentially, the current into the ADS8411 charges the internal capacitor array during the sample period. After this capacitance has been fully charged, there is no further input current. The source of the analog input voltage must be able to charge the input capacitance (25 pF) to an 16-bit settling level within the acquisition time (100 ns) of the device. When the converter goes into the hold mode, the input impedance is greater than 1 GΩ. Care must be taken regarding the absolute analog input voltage. To maintain the linearity of the converter, the +IN and –IN inputs and the span (+IN – (–IN)) should be within the limits specified. Outside of these ranges, the converter's linearity may not meet specifications. To minimize noise, low bandwidth input signals with low-pass filters should be used. Care should be taken to ensure that the output impedance of the sources driving +IN and –IN inputs are matched. If this is not observed, the two inputs could have different setting time. This may result in offset error, gain error and linearity error which varies with temperature and input voltage. DIGITAL INTERFACE Timing And Control See the timing diagrams in the specifications section for detailed information on timing signals and their requirements. The ADS8411 uses an internal oscillator generated clock which controls the conversion rate and in turn the throughput of the converter. No external clock input is required. Conversions are initiated by bringing the CONVST pin low for a minimum of 20 ns (after the 20 ns minimum requirement has been met, the CONVST pin can be brought high), while CS is low. The ADS8411 switches from the sample to the hold mode on the falling edge of the CONVST command. A clean and low jitter falling edge of this signal is important to the performance of the converter. The BUSY output is brought high after CONVST goes low. BUSY stays high throughout the conversion process and returns low when the conversion has ended. Sampling starts with the falling edge of the BUSY signal when CS is tied low or starts with the falling edge of CS when BUSY is low. Both RD and CS can be high during and before a conversion with one exception (CS must be low when CONVST goes low to initiate a conversion). Both the RD and CS pins are brought low in order to enable the parallel output bus with the conversion. 20 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 PRINCIPLES OF OPERATION (continued) Reading Data The ADS8411 outputs full parallel data in straight binary format as shown in Table 1. The parallel output is active when CS and RD are both low. There is a minimal quiet zone requirement around the falling edge of CONVST. This is 50 ns prior to the falling edge of CONVST and 40 ns after the falling edge. No data read should be attempted within this zone. Any other combination of CS and RD sets the parallel output to 3-state. BYTE is used for multiword read operations. BYTE is used whenever lower bits of the converter result are output on the higher byte of the bus. Refer to Table 1 for ideal output codes. Table 1. Ideal Input Voltages and Output Codes DESCRIPTION ANALOG VALUE DIGITAL OUTPUT Full scale range Vref STRAIGHT BINARY Least significant bit (LSB) Vref/65536 Full scale Vref– 1 LSB 1111 1111 1111 1111 FFFF Midscale Vref/2 1000 0000 0000 0000 8000 Midscale – 1 LSB Vref/2 – 1 LSB 0111 1111 1111 1111 7FFF Zero 0V 0000 0000 0000 0000 0000 BINARY CODE HEX CODE The output data is a full 16-bit word (D15–D0) on DB15–DB0 pins (MSB-LSB) if BYTE is low. The result may also be read on an 8-bit bus for convenience. This is done by using only pins DB15-DB8. In this case two reads are necessary: the first as before, leaving BYTE low and reading the 8 most significant bits on pins DB15-DB8, then bringing BYTE high. When BYTE is high, the low bits (D7–D0) appear on pins DB15–D8. These multiword read operations can be done with multiple active RD (toggling) or with RD tied low for simplicity. Table 2. Conversion Data Readout BYTE DATA READ OUT DB15–DB8 Pins DB7-DB0 Pins High D7–D0 All one's Low D15–D8 D7-D0 RESET RESET is an asynchronous active low input signal (that works independently of CS). Minimum RESET low time is 25 ns. Current conversion will be aborted no later than 50 ns after the converter is in the reset mode. In addition, all output latches are cleared (set to zero's) after RESET. The converter goes back to normal operation mode no later than 20 ns after RESET input is brought high. The converter starts the first sampling period 20 ns after the rising edge of RESET. Any sampling period except for the one immediately after a RESET is started with the falling edge of the previous BUSY signal or the falling edge of CS, whichever is later. Another way to reset the device is through the use of the combination of CS and CONVST. This is useful when the dedicated RESET pin is tied to the system reset but there is a need to abort only the conversion in a specific converter. Since the BUSY signal is held high during the conversion, either one of these conditions triggers an internal self-clear reset to the converter just the same as a reset via the dedicated RESET pin. The reset does not have to be cleared as for the dedicated RESET pin. A reset can be started with either of the two following steps. • Issue a CONVST when CS is low and a conversion is in progress. The falling edge of CONVST must satisfy the timing as specified by the timing parameter tsu(AB) mentioned in the timing characteristics table to ensure a reset. The falling edge of CONVST starts a reset. Timing is the same as a reset using the dedicated RESET pin except the instance of the falling edge is replaced by the falling edge of CONVST. • Issue a CS while a conversion is in progress. The falling edge of CS must satisfy the timing as specified by the timing parameter tsu(AB) mentioned in the timing characteristics table to ensure a reset.The falling edge of CS causes a reset. Timing is the same as a reset using the dedicated RESET pin except the instance of the falling edge is replaced by the falling edge of CS. 21 ADS8411 www.ti.com SLAS369B – APRIL 2002 – REVISED DECEMBER 2004 POWER-ON INITIALIZATION RESET is not required after power on. An internal power-on-reset circuit generates the reset. To ensure that all of the registers are cleared, the three conversion cycles must be given to the converter after power on. LAYOUT For optimum performance, care should be taken with the physical layout of the ADS8411 circuitry. As the ADS8411 offers single-supply operation, it is often used in close proximity with digital logic, microcontrollers, microprocessors, and digital signal processors. The more digital logic present in the design and the higher the switching speed, the more difficult it is to achieve good performance from the converter. The basic SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground connections and digital inputs that occur just prior to latching the output of the analog comparator. Thus, driving any single conversion for an n-bit SAR converter, there are at least n windows in which large external transient voltages can affect the conversion result. Such glitches might originate from switching power supplies, nearby digital logic, or high power devices. The degree of error in the digital output depends on the reference voltage, layout, and the exact timing of the external event. On average, the ADS8411 draws very little current from an external reference, as the reference voltage is internally buffered. If the reference voltage is external and originates from an op amp, make sure that it can drive the bypass capacitor or capacitors without oscillation. A 0.1-µF bypass capacitor and a 1-µF storage capacitor are recommended from pin 1 (REFIN) directly to pin 48 (REFM). REFM and AGND should be shorted on the same ground plane under the device. The AGND and BDGND pins should be connected to a clean ground point. In all cases, this should be the analog ground. Avoid connections which are close to the grounding point of a microcontroller or digital signal processor. If required, run a ground trace directly from the converter to the power supply entry point. The ideal layout consists of an analog ground plane dedicated to the converter and associated analog circuitry. As with the AGND connections, +VA should be connected to a 5-V power supply plane or trace that is separate from the connection for digital logic until they are connected at the power entry point. Power to the ADS8411 should be clean and well bypassed. A 0.1-µF ceramic bypass capacitor should be placed as close to the device as possible. See Table 3 for the placement of the capacitor. In addition, a 1-µF to 10-µF capacitor is recommended. In some situations, additional bypassing may be required, such as a 100-µF electrolytic capacitor or even a Pi filter made up of inductors and capacitors—all designed to essentially low-pass filter the 5-V supply, removing the high frequency noise. Table 3. Power Supply Decoupling Capacitor Placement POWER SUPPLY PLANE SUPPLY PINS CONVERTER ANALOG SIDE CONVERTER DIGITAL SIDE Pin pairs that require shortest path to decoupling capacitors (4,5), (8,9), (10,11), (13,15), (43,44), (45,46) (24,25), (34, 35) Pins that require no decoupling 12, 14 37 22 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. 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