SBAS312A − JANUARY 2005 − REVISED APRIL 2005 FEATURES D 16-Bit Resolution D 14-Bit Linearity D ±2.5V Input Range at 2.5V D Internal Reference Voltage: 2% D Gain Error: 0.5% D Two Independent Delta-Sigma Modulators D Two Input Reference Buffers D On-Chip 20MHz Oscillator D Selectable Internal or External Clock D Operating Temperature Range: D −40°C to +85°C QFN-24 (4x4) Package APPLICATIONS D Motor Control D Current Measurement D Industrial Process Control D Instrumentation D Resolver DESCRIPTION The ADS1205 is a two-channel, high-performance, delta-sigma (∆Σ) modulator with more than 98dB dynamic range, operating from a single +5V supply. The differential inputs are ideal for direct connection to transducers in an industrial environment. With the appropriate digital filter and modulator rate, the device can be used to achieve 16-bit analog-to-digital (A/D) conversion with no missing codes. Effective resolution of 14 bits can be obtained with a digital filter bandwidth of 40kHz at a modulator rate of 10MHz. The ADS1205 is designed for use in high-resolution measurement applications including current measurements, smart transmitters, industrial process control, and resolvers. It is available in a QFN-24 (4x4) package. AV DD CH A+ CH A− BV DD OUT A 2nd−Order ∆Σ Modulator Output Interface Circuit CLKOUT REFIN A CH B+ CH B− OUT B 2nd−Order ∆Σ Modulator Divider REFIN B Clock Select Out REFOUT CLKIN CLKSEL EN Reference Voltage 2.5V RC Oscillator 20MHz AGND BGND 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. All trademarks are the property of their respective owners. Copyright 2005, Texas Instruments Incorporated !"#$ % & % '(& ) & &% '&%& ' * % + # ,) & '& &, & % ') www.ti.com www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 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. Package/Ordering Information For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI web site at www.ti.com. ABSOLUTE MAXIMUM RATINGS over operating free-air temperature range unless otherwise noted(1) ADS1205 UNIT Supply voltage, AGND to AVDD −0.3 to 6 V Supply voltage, BGND to BVDD −0.3 to 6 V AGND − 0.3 to AVDD + 0.3 AGND − 0.3 to AVDD + 0.3 V Reference input voltage with respect to AGND Digital input voltage with respect to BGND BGND − 0.3 to BVDD + 0.3 V ±0.3 V Analog input voltage with respect to AGND Ground voltage difference, AGND to BGND V Voltage differences, BVDD to AGND −0.3 to 6 V Input current to any pin except supply ±10 mA Power dissipation See Dissipation Rating table Operating virtual junction temperature range, TJ −40 to +150 °C Operating free-air temperature range, TA −40 to +85 °C Storage temperature range, TSTG −65 to +150 °C (1) 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. DISSIPATION RATINGS PACKAGE TA ≤ 25°C POWER RATING DERATING FACTOR ABOVE TA = 25°C(1) 21.929mW/°C TA = 70°C POWER RATING TA = 85°C POWER RATING QFN-24 (4x4) 2193mW 1206mW 877.2mW (1) This is the inverse of the traditional junction-to-ambient thermal resistance (Rq JA). Thermal resistances are not production tested and are for informational purposes only. RECOMMENDED OPERATING CONDITIONS PARAMETER Supply voltage, AGND to AVDD Supply voltage, BGND to BVDD MIN NOM MAX UNIT 4.5 5 5.5 V 3.6 V Low-Voltage Levels 2.7 5V Logic Levels 4.5 5 5.5 V 0.5 2.5 2.6 V Reference input voltage Operating common-mode signal −IN Analog inputs +IN − (−IN) 2.5 External clock(1) 16 Operating junction temperature range, TJ (1) With reduced accuracy, clock can go from 1MHz up to 33MHz; see Typical Characteristics. −40 2 V ±0.8 × REFIN 20 V 24 MHz 105 °C www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 ELECTRICAL CHARACTERISTICS Over recommended operating free-air temperature range at −40°C to +85°C, AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. PARAMETER Resolution TEST CONDITIONS MIN ADS1205I TYP(1) MAX 16 UNITS Bits DC Accuracy INL Integral linearity error(2) −1.4 ±3 −0.002 ±0.005 6 Integral linearity match DNL VOS TCVOS GERR 0.009 Differential nonlinearity(3) Input offset error(4) LSB % FSR ±1 LSB −1.2 ±3 mV Input offset error match 0.1 2 mV Input offset error drift Gain error(4) 1.1 8 µV/°C −0.01 ±0.5 % FSR 0.09 0.5 Referenced to VREF Gain error match TCGERR PSRR LSB % FSR Gain error drift % FSR 1.3 ppm/°C 78 dB Power-supply rejection ratio 4.75V < AVDD < 5.25V Full-scale differential range (CH x+) − (CH x−); CH x− = 2.5V ±2.5 V Specified differential range (CH x+) − (CH x−); CH x− = 2.5V ±2 V Analog Input FSR Maximum operating input range(3) 0 Input capacitance Common-mode Input leakage current CLK turned off 3 100 Differential input capacitance Common-mode rejection ratio BW Bandwidth V pF ±1 Differential input resistance CMRR AVDD nA kΩ 2.5 pF At DC 108 dB VIN = ±1.25VPP at 40kHz FS sine wave, −3dB 117 dB 50 MHz Sampling Dynamics Internal clock frequency CLKSEL = 1 8 9.8 12 MHz External clock frequency(5) CLKSEL = 0 1 20 24 MHz THD Total harmonic distortion −96.6 −88 dB SFDR Spurious-free dynamic range VIN = ±2VPP at 5kHz VIN = ±2VPP at 5kHz SNR Signal-to-noise ratio SINAD Signal-to-noise + distortion VIN = ±2VPP at 5kHz VIN = ±2VPP at 5kHz Channel-to-channel isolation(3) VIN = ±2VPP at 50kHz CLKIN AC Accuracy ENOB Effective number of bits 92 98 dB 86 88.9 dB 85 88.2 dB 14 100 dB 14.5 Bits (1) All typical values are at TA = +25°C. (2) Integral nonlinearity is defined as the maximum deviation of the line through the end points of the specified input range of the transfer curve for CH x+ = −2V to +2V at 2.5V, expressed either as the number of LSBs or as a percent of measured input range (4V). (3) Ensured by design. (4) Maximum values, including temperature drift, are ensured over the full specified temperature range. (5) With reduced accuracy, the clock frequency can go from 1MHz to 33MHz. (6) Applicable for 5.0V nominal supply: BVDD (min) = 4.5V and BVDD (max) = 5.5V. (7) Applicable for 3.0V nominal supply: BVDD (min) = 2.7V and BVDD (max) = 3.6V. 3 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 ELECTRICAL CHARACTERISTICS (continued) Over recommended operating free-air temperature range at −40°C to +85°C, AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. PARAMETER Voltage Reference Output VREFOUT Reference voltage output dVREFOUT/dT Output voltage temperature drift Output voltage noise TEST CONDITIONS −40°C to +85°C MIN 2.450 ADS1205I TYP(1) MAX 2.5 2.550 UNITS V ±20 ppm/°C f = 0.1Hz to 10Hz, CL = 10µF 10 µVrms f =10Hz to 10kHz, CL = 10µF 12 µVrms dB PSRR Power-supply rejection ratio 60 IOUT ISC Output current 10 µA Short-circuit current 0.5 mA 100 µs Turn-on settling time to 0.1% at CL = 0 Voltage Reference Input VIN Reference voltage input 0.5 Reference input resistance 2.5 2.6 100 Reference input capacitance 5 pF 1 µA BVDD+0.3 0.3×BVDD V ±50 nA Reference input current Digital Inputs(6) Logic family VIH VIL High-level input voltage IIN CI Input current V MΩ CMOS with Schmitt Trigger 0.7×BVDD −0.3 Low-level input voltage VI = BVDD or GND Input capacitance 5 V pF Digital Outputs(6) Logic family VOH VOL High-level output voltage CO CL Output capacitance Low-level output voltage CMOS BVDD = 4.5V, IOH = −100µA BVDD = 4.5V, IOL = +100µA 4.44 V 0.5 5 Load capacitance Data format V pF 30 pF Bit Stream (1) All typical values are at TA = +25°C. (2) Integral nonlinearity is defined as the maximum deviation of the line through the end points of the specified input range of the transfer curve for CH x+ = −2V to +2V at 2.5V, expressed either as the number of LSBs or as a percent of measured input range (4V). (3) Ensured by design. (4) Maximum values, including temperature drift, are ensured over the full specified temperature range. (5) With reduced accuracy, the clock frequency can go from 1MHz to 33MHz. (6) Applicable for 5.0V nominal supply: BVDD (min) = 4.5V and BVDD (max) = 5.5V. (7) Applicable for 3.0V nominal supply: BVDD (min) = 2.7V and BVDD (max) = 3.6V. 4 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 ELECTRICAL CHARACTERISTICS (continued) Over recommended operating free-air temperature range at −40°C to +85°C, AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. PARAMETER Digital Inputs(7) MIN TEST CONDITIONS Logic family ADS1205I TYP(1) MAX UNITS LVCMOS VIH VIL High-level input voltage Low-level input voltage BVDD = 3.6V BVDD = 2.7V IIN CI Input current VI = BVDD or GND 2 −0.3 Input capacitance BVDD+0.3 0.8 V ±50 nA 5 V pF Digital Outputs(7) Logic family LVCMOS VOH VOL High-level output voltage CO CL Output capacitance BVDD = 2.7V, IOH = −100µA BVDD = 2.7V, IOL = +100µA Low-level output voltage BVDD−0.2 V 0.2 5 Load capacitance Data format V pF 30 pF Bit Stream Power Supply AVDD BVDD AIDD BIDD Analog supply voltage Buffer I/O supply voltage Analog operating supply current Buffer I/O operating supply current Power dissipation 4.5 5.5 V Low-voltage levels 2.7 3.6 V 5V logic levels 4.5 5.5 V CLKSEL = 1 11.8 16 mA CLKSEL = 0 11.4 15.5 mA 2 mA BVDD = 3V, CLKOUT = 10MHz BVDD = 5V, CLKOUT = 10MHz 2 mA CLKSEL = 0 57 77.5 mW CLKSEL = 1 59 80 mW (1) All typical values are at TA = +25°C. (2) Integral nonlinearity is defined as the maximum deviation of the line through the end points of the specified input range of the transfer curve for CH x+ = −2V to +2V at 2.5V, expressed either as the number of LSBs or as a percent of measured input range (4V). (3) Ensured by design. (4) Maximum values, including temperature drift, are ensured over the full specified temperature range. (5) With reduced accuracy, the clock frequency can go from 1MHz to 33MHz. (6) Applicable for 5.0V nominal supply: BVDD (min) = 4.5V and BVDD (max) = 5.5V. (7) Applicable for 3.0V nominal supply: BVDD (min) = 2.7V and BVDD (max) = 3.6V. EQUIVALENT INPUT CIRCUIT BVDD AVDD R ON 650Ω C(SAMPLE) 1pF AIN DIN Diode Turn−On Voltage: 0.35V AGND Equivalent Analog Input Circuit BGND Equivalent Digital Input Circuit 5 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 PIN ASSIGNMENTS 19 NC 20 CH A+ 21 CH A− 22 CH B− 23 CH B+ 24 NC RGE PACKAGE QFN−24 (TOP VIEW) REFIN B 1 18 REFIN A AGND 2 17 AGND AVDD 3 16 AVDD AVDD 4 15 AVDD AGND 5 14 REFOUT CLKSEL 6 13 AGND 7 8 9 10 11 12 CLKIN BVDD BGND CLKOUT OUT B OUT A ADS1205 Terminal Functions TERMINAL NAME REFIN B NO. I/O 1 I AGND 2, 5, 13, 17 AVDD 3, 4, 15, 16 DESCRIPTION Reference voltage input of channel B: pin for external reference voltage Analog ground Analog power supply; nominal 5V CLKSEL 6 I Clock select between internal clock (CLKSEL = 1) or external clock (CLKSEL = 0) CLKIN 7 I External clock input BVDD 8 Digital interface power supply; from 2.7V to 5.5V BGND 9 CLKOUT 10 O System clock output OUT B 11 O Bit stream from channel B modulator OUT A 12 O Bit stream from channel A modulator REFOUT 14 O Reference voltage output: output pin of the internal reference source; nominal 2.5V REFIN A 18 I Reference voltage input of channel A: pin for external reference voltage NC Interface ground 19, 24 No connection; this pin is left unconnected CH A+ 20 I Analog input of channel A: noninverting input CH A− 21 I Analog input of channel A: inverting input CH B− 22 I Analog input of channel B: inverting input CH B+ 23 I Analog input of channel B: noninverting input 6 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 PARAMETER MEASUREMENT INFORMATION tC1 CLKIN t W1 tC2 tD1 tD2 CLKOUT tD3 tW2 tD4 OUT x Figure 1. ADS1205 Timing Diagram TIMING REQUIREMENTS(1) over recommended operating free-air temperature range at −40°C to +85°C, AVDD = 5V, and BVDD = 2.7 to 5V, unless otherwise noted. MIN 41.6(2) MAX UNIT 1000 ns CLKIN high time: (CLKSEL = 0) 10 83 tC1 − 10 125 ns CLKOUT period using internal oscillator (CLKSEL = 1) 2 × tC1 (tC2/2) − 5 0 (tC2/2) + 5 10 ns 0 10 ns (tC2/4) − 8 tW1 − 3 (tC2/4) + 8 tW1 + 7 ns PARAMETER tC1 tW1 CLKIN period: (CLKSEL = 0) tC2 CLKOUT period using external clock (CLKSEL = 0) tW2 tD1 CLKOUT high time tD2 tD3 CLKOUT falling edge delay after CLKIN rising edge: (CLKOUT = 0) CLKOUT rising edge delay after CLKIN rising edge: (CLKOUT = 0) Data valid delay after rising edge of CLKOUT (CLKSEL = 1) ns ns ns tD4 Data valid delay after rising edge of CLKOUT (CLKSEL = 0) ns (1) All input signals are specified with tR = tF = 5ns (10% to 90% of BVDD) and timed from a voltage level of (VIL + VIH)/2. See Figure 1. (2) With reduced accuracy, the minimum clock period can go down to 30ns. 7 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 TYPICAL CHARACTERISTICS AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. 0.00259 1.7 0.00259 1.2 0.00183 1.2 0.00183 0.70 0.00107 0.70 0.00107 0.20 0.00031 +25_C −0.00046 +85_C −0.8 −1.3 −1.8 −2.5 −2.0 −1.5 −1.0 −0.5 0 0.5 1.0 Differential Input Voltage (V) 2.0 0.00031 −0.3 −0.00122 −0.8 −0.00198 −1.3 −40_C 1.5 0.20 +25_C −0.00046 −0.00122 −0.00198 −1.8 −2.5 −2.0 −1.5 −1.0 −0.5 0 0.5 1.0 Differential Input Voltage (V) −0.00275 2.5 Figure 2 −40_C 1.5 2.0 −0.00275 2.5 Figure 3 INTEGRAL LINEARITY MATCH OF CHANNELS vs INPUT SIGNAL INTEGRAL LINEARITY vs TEMPERATURE 0 0.00046 −0.2 −0.00031 0.2 0.00031 −0.4 −0.00061 0.1 0.00015 −0.6 −0.00092 −0.8 −0.00122 0.3 CLKIN = 20MHz 0 CLKIN = 32MHz 0 INL (%) INL (LSB) 0.00061 0.4 INL (LSB) +85_C −0.1 −0.00015 −0.2 −0.00031 −1.2 −0.3 −0.00046 −1.4 −0.4 −2.5 −2.0 −1.5 −1.0 −0.5 0 0.5 1.0 Differential Input Voltage (V) 1.5 2.0 −0.00061 2.5 −1.0 0 −0.00153 CLKIN = 32MHz −0.00183 −0.00214 CLKIN = 20MHz −1.6 −40 −20 0 Figure 4 20 40 Temperature (_ C) 60 80 −0.00244 100 Figure 5 OFFSET vs TEMPERATURE OFFSET MATCH vs TEMPERATURE −1.0 0.15 0.14 0.13 Offset Match (mV) Offset (mV) −1.05 −1.10 −1.15 CLKIN = 32MHz −1.20 CLKIN = 20MHz 0.09 0.08 0.06 CLKIN = 20MHz −20 0 20 40 Temperature (_C) Figure 6 8 0.11 0.10 0.07 −1.25 −1.30 −40 CLKIN = 32MHz 0.12 60 80 100 0.05 −40 −20 0 20 40 Temperature (_ C) Figure 7 60 80 100 INL (%) −0.3 INL (LSB) 1.7 INL (%) INTEGRAL NONLINEARITY vs INPUT SIGNAL (CLKIN = 32MHz) INL (%) INL (LSB) INTEGRAL NONLINEARITY vs INPUT SIGNAL (CLKIN = 20MHz) www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 TYPICAL CHARACTERISTICS (continued) AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. OFFSET vs POWER SUPPLY REFERENCE VOLTAGE vs TEMPERATURE −0.8 2.510 2.508 2.506 2.504 CLKIN = 32MHz VREF (V) Offset (mV) −1.0 −1.2 CLKIN = 20MHz 2.502 2.500 2.498 2.496 −1.4 2.494 2.492 −1.6 4.50 2.490 4.75 5.00 5.25 5.50 −40 −20 0 Power Supply (V) Figure 8 0.20 0.120 0.15 0.115 0.10 0.110 0.05 CLKIN = 20MHz −0.05 CLKIN = 32MHz −0.10 0.100 0.080 40 60 80 100 CLKIN = 32MHz 0.075 −40 100 −20 0 Temperature (_ C) 20 40 60 Temperature (_C) Figure 10 Figure 11 SIGNAL−TO−NOISE RATIO vs TEMPERATURE 89.0 80 CLKIN = 20MHz 0.090 −0.20 20 100 0.095 0.085 0 80 0.105 −0.15 −20 60 GAIN MATCH vs TEMPERATURE 0.125 Gain Match (%) Gain (%) GAIN vs TEMPERATURE −0.25 −40 40 Figure 9 0.25 0 20 Temperature (_ C) SIGNAL−TO−NOISE + DISTORTION vs TEMPERATURE 89.2 CLKIN = 20MHz 88.9 89.0 88.8 88.8 88.6 SINAD (dB) SNR (dB) 88.7 CLKIN = 32MHz 88.5 88.4 88.3 88.4 CLKIN = 20MHz 88.2 88.0 88.2 88.1 88.6 CLKIN = 32MHz 4VPP 5kHz 4VPP 5kHz 87.8 88.0 87.6 −40 −20 0 20 40 Temperature (_C) Figure 12 60 80 100 −40 −20 0 20 40 Temperature (_C) 60 80 100 Figure 13 9 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 TYPICAL CHARACTERISTICS (continued) AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. SPURIOUS FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs TEMPERATURE (CLKIN = 20MHz) SPURIOUS FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs TEMPERATURE (CLKIN = 32MHz) 101 −101 101 99 −99 99 SFDR −97 97 THD 95 −95 −93 −91 91 89 −89 89 −87 87 −20 0 20 40 Temperature (_C) 60 80 −97 −95 −91 −85 100 −99 THD 93 91 85 −40 −101 95 −93 4VPP 5kHz −103 SFDR 97 93 87 −105 THD (dB) 103 SFDR (dB) 105 −103 THD (dB) −105 103 SFDR (dB) 105 −89 4VPP 5kHz 85 −40 −20 Figure 14 −87 0 20 40 Temperature (_C) 60 80 −85 100 Figure 15 SIGNAL−TO−NOISE AND DISTORTION AND SIGNAL−TO−NOISE RATIO vs INPUT FREQUENCY (CLKIN = 20MHz) SIGNAL−TO−NOISE AND DISTORTION AND SIGNAL−TO−NOISE RATIO vs INPUT FREQUENCY (CLKIN = 32MHz) 100 100 98 SINAD and SNR (dB) 94 92 SNR 90 88 SINAD 86 84 82 90 SNR SINAD 85 OSR = 256 Sinc3 Filter 80 100 OSR = 256 Sinc3 Filter 1k Input Frequency (kHz) 80 100 100k 100k Figure 17 SPURIOUS FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY (CLKIN = 20MHz) SPURIOUS FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY (CLKIN = 32MHz) −120 120 −120 110 −110 110 −110 SFDR −100 100 SFDR (dB) 120 SFDR 100 −90 OSR = 256 Sinc3 Filter 80 100 1k 10k Input Frequency (Hz) Figure 18 −80 100k −100 THD THD 90 10 1k 10k Input Frequency (kHz) Figure 16 THD (dB) SFDR (dB) 95 −90 90 OSR = 256 Sinc3 Filter 80 100 1k 10k Input Frequency (Hz) Figure 19 −80 100k THD (dB) SINAD and SNR (dB) 96 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 TYPICAL CHARACTERISTICS (continued) AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. FREQUENCY SPECTRUM (4096 point FFT fIN = 5kHz, 4VPP ) 0 0 −20 −20 −40 −40 Magnitude (dB) Magnitude (dB) FREQUENCY SPECTRUM (4096 point FFT fIN = 1kHz, 4VPP ) −60 −80 −100 −60 −80 −100 −120 −120 −140 −140 −160 −160 0 2 4 6 8 10 12 14 16 0 18 19 2 4 6 Frequency (kHz) Figure 20 Sinc2 Filter 98 16 86 15 14 Current (mA) 74 SNR (dB) 12 14 16 18 19 CLKSEL = 0, CLKIN = 32MHz 13 10 62 8 50 6 38 4 26 9 14 8 12 11 CLKSEL = 0, CLKIN = 20MHz 10 CLKSEL = 1 2 10 100 1k −40 Decimation Ratio (OSR) 0 20 40 60 80 100 Figure 23 COMMON−MODE REJECTION RATIO vs FREQUENCY POWER−SUPPLY REJECTION RATIO vs FREQUENCY 100 120 90 PSRR (dB) 130 110 100 90 100 −20 Temperature (_C) Figure 22 CMRR (dB) ENOB (Bits) 12 POWER−SUPPLY CURRENT vs TEMPERATURE Sinc3 Filter 14 10 Figure 21 EFFECTIVE NUMBER OF BITS vs DECIMATION RATIO 16 8 Frequency (kHz) 80 70 1k 10k 100k Input Frequency (kHz) Figure 24 1M 60 100 1k Frequency of Power Supply (kHz) 10k Figure 25 11 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 TYPICAL CHARACTERISTICS (continued) AVDD = 5V, BVDD = 3V, CH x+ = 0.5V to 4.5V, CH x− = 2.5V, REFIN = REFOUT = internal +2.5V, CLKIN = 20MHz, and 16-bit Sinc3 filter with decimation by 256, unless otherwise noted. 10.8 10.1 10.6 10.0 10.4 9.9 10.2 10.0 9.8 9.6 9.8 9.7 9.6 9.5 9.4 9.4 9.2 9.3 9.0 −40 −20 9.2 0 20 40 Temperature (_ C) Figure 26 12 CLOCK FREQUENCY vs POWER SUPPLY 10.2 CLKOUT (MHz) CLKOUT (MHz) CLOCK FREQUENCY vs TEMPERATURE 11.0 60 80 100 4.5 4.75 5 Power Supply (V) Figure 27 5.25 5.5 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 GENERAL DESCRIPTION The ADS1205 is a two-channel, 2nd-order, CMOS device with two delta-sigma modulators, designed for medium- to high-resolution A/D signal conversions from DC to 39kHz (filter response −3dB) if an oversampling ratio (OSR) of 64 is chosen. The output of the converter (OUTX) provides a stream of digital ones and zeros. The time average of this serial output is proportional to the analog input voltage. The modulator shifts the quantization noise to high frequencies. A low-pass digital filter should be used at the output of the delta-sigma modulator. The filter serves two functions. First, it filters out high-frequency noise. Second, the filter converts the 1-bit data stream at a high sampling rate into a higher-bit data word at a lower rate (decimation). An application-specific integrated circuit (ASIC) or field-programmable gate array (FPGA) could be used to implement the digital filter. Figure 28 and Figure 29 show typical application circuits with the ADS1205 connected to an FPGA or ASIC. The overall performance (that is, speed and accuracy) depends on the selection of an appropriate OSR and filter type. A higher OSR produces greater output accuracy while operating at a lower refresh rate. Alternatively, a lower OSR produces lower output accuracy, but operates at a higher refresh rate. This system allows flexibility with the digital filter design and is capable of A/D conversion results that have a dynamic range exceeding 98dB with an OSR = 256. 2 kΩ AVDD +5V BVDD 5kΩ ±5V 27Ω 0.1µF CH A+ OPA 2350 0.1nF 5kΩ CH A− 2nd−Order ∆Σ Modulator 2kΩ OUT A OUT B Output Interface Circuit FPGA or ASIC REFIN A CLKOUT 2kΩ CH B+ CH B− +5V 2nd−Order ∆Σ Modulator BVDD 0.1µF BGND 5kΩ ±5V 27Ω 0.1µF REFIN B OPA 2350 Divider 0.1nF 5kΩ +3V 2kΩ +3V Clock Select CLKIN CLKSEL +5V AVDD Out REFOUT Reference Voltage 2.5V +5V EN RC Oscillator 20MHz AVDD AVDD AVDD AGND AGND AGND AGND +5V +5V 0.1µF 0.1µF 0.1µF 0.1µF 0.1µF +5V OP A 336 0.1µF Figure 28. Single-Ended Connection Diagram for the ADS1205 Delta-Sigma Modulator 13 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 AVDD +5V BVD D 27Ω R1 CH A+ OP A 435 4 IN+ CH A− 0.1nF 2nd−Order ∆Σ Modulator R2 OUT A OUT B Output Interface Circuit FPGA or ASIC REFIN A CLKOUT +5V CH B+ 27Ω R1 OP A 435 4 CH B− 2nd−Order ∆Σ Modulator +3V BVD D 0.1µF BGND IN− REFIN B R2 Divider +5V +3V 27Ω R1 Clock Select OP A 435 4 IN+ CLKIN CLKSEL 0.1nF +5V R2 AVD D Out +5V 27Ω R1 OP A 435 4 IN− REFOUT R2 Reference Voltage 2.5V +5V EN RC Oscillator 20MHz AVD D AVD D AVD D AGND AGND AGND AGND +5V +5V 0.1µF 0.1µF 0.1µF 0.1µF +5V OP A33 6 0.1µF Figure 29. Differential Connection Diagram for the ADS1205 Delta-Sigma Modulator 14 0.1µF www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 THEORY OF OPERATION The differential analog input of the ADS1205 is implemented with a switched-capacitor circuit. This circuit implements a 2nd-order modulator stage, which digitizes the analog input signal into a 1-bit output stream. The clock source can be internal as well as external. Different frequencies for this clock allow for a variety of solutions and signal bandwidths. Every analog input signal is continuously sampled by the modulator and compared to a reference voltage that is applied to the REFINx pin. A digital stream, which accurately represents the analog input voltage over time, appears at the output of the corresponding converter. ANALOG INPUT STAGE Analog Input The topology of the analog inputs of ADS1205 is based on a fully differential switched-capacitor architecture. This input stage provides the mechanism to achieve low system noise, high common-mode rejection (108dB), and excellent power-supply rejection. The input impedance of the analog input is dependent on the modulator clock frequency (fCLK), which is also the sampling frequency of the modulator. Figure 30 shows the basic input structure of one channel of the ADS1205. The relationship between the input impedance of the ADS1205 and the modulator clock frequency is: Z IN + 100kW f MODń10MHz (1) The input impedance becomes a consideration in designs where the source impedance of the input signal is high. This high impedance may cause degradation in gain, linearity, and THD. The importance of this effect depends on the desired system performance. There are two restrictions on the analog input signals, CH x+ and CH x−. If the input voltage exceeds the range (GND – 0.3V) to (VDD + 0.3V), the input current must be limited to 10mA because the input protection diodes on the front end of the converter will begin to turn on. In addition, the linearity and the noise performance of the device are ensured only when the differential analog voltage resides within ±2V (with VREF as a midpoint); however, the FSR input voltage is ±2.5V. Modulator The ADS1205 can be operated in two modes. When CKLSEL = 1, the two modulators operate using the internal clock, which is fixed at 20MHz. When CKLSEL = 0, the modulators operate using an external clock. In both modes, the clock is divided by two internally and functions as the modulator clock. The frequency of the external clock can vary from 1MHz to 33MHz to adjust for the clock requirements of the application. The modulator topology is fundamentally a 2nd-order, switched-capacitor, delta-sigma modulator, such as the one conceptualized in Figure 31. The analog input voltage and the output of the 1-bit digital-to-analog converter (DAC) are differentiated, providing analog voltages at X2 and X3. The voltages at X2 and X3 are presented to their individual integrators. The output of these integrators progresses in a negative or positive direction. When the value of the signal at X4 equals the comparator reference voltage, the output of the comparator switches from negative to positive, or positive to negative, depending on its original state. When the output value of the comparator switches from high to low or vice versa, the 1-bit DAC responds on the next clock pulse by changing its analog output voltage at X6, causing the integrators to progress in the opposite direction. The feedback of the modulator to the front end of the integrators forces the value of the integrator output to track the average of the input. 650Ω AIN+ 1.2pF 0.4pF VCM Switching Frequency = CLK 0.4pF AIN− High Impedance > 1GΩ 650Ω 1.2pF High Impedance > 1GΩ Figure 30. Input Impedance of the ADS1205 15 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 fCLK X2 X(t) Integrator 1 X3 Integrator 2 X4 DATA fS VREF Comparator X6 D/A Converter Figure 31. Block Diagram of the 2nd-Order Modulator DIGITAL OUTPUT A differential input signal of 0V will ideally produce a stream of ones and zeros that are high 50% of the time and low 50% of the time. A differential input of +2V produces a stream of ones and zeros that are high 80% of the time. A differential input of –2V produces a stream of ones and zeros that are high 20% of the time. The input voltage versus the output modulator signal is shown in Figure 32. DIGITAL INTERFACE INTRODUCTION The analog signal connected to the input of the delta-sigma modulator is converted using the clock signal applied to the modulator. The result of the conversion, or modulation, is generated and sent to the OUTx pin from the delta-sigma modulator. In most applications where a direct connection is realized between the delta-sigma modulator and an ASIC or FPGA (each with an implemented filter), the two standard signals per modulator (CLKOUT and OUTx) are provided from the modulator. The output clock signal is equal for both modulators. If CLKSEL = 1, CLKIN must always be set either high or low. MODES OF OPERATION The system clock of the ADS1205 is 20MHz by default. The system clock can be provided either from the internal 20MHz RC oscillator or from an external clock source. For this purpose, the CLKIN pin is provided; it is controlled by the mode setting, CLKSEL. The system clock is divided by two for the modulator clock. Therefore, the default clock frequency of the modulator is 10MHz. With a possible external clock range of 1MHz to 33MHz, the modulator operates between 500kHz and 16.5MHz. Modulator Output +FS (Analog Input) −FS (Analog Input) Analog Input Figure 32. Analog Input vs Modulator Output of the ADS1205 16 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 FILTER USAGE 0 A very simple filter, built with minimal effort and hardware, is the Sinc3 filter: ǒ Ǔ −OSR H(z) + 1 * z −1 1*z OSR = 32 f DATA = 10MHz/32 = 312.5kHz −3dB: 81.9kHz −10 −20 Gain (dB) The modulator generates only a bitstream, which does not output a digital word like an A/D converter. In order to output a digital word equivalent to the analog input voltage, the bitstream must be processed by a digital filter. −30 −40 −50 −60 3 −70 (2) This filter provides the best output performance at the lowest hardware size (for example, a count of digital gates). For oversampling ratios in the range of 16 to 256, this is a good choice. All the characterizations in the data sheet are also done using a Sinc3 filter with an oversampling ratio of OSR = 256 and an output word length of 16 bits. −80 0 This performance can be improved, for example, by a cascaded filter structure. The first decimation stage can be a Sinc3 filter with a low OSR and the second stage a high-order filter. For more information, see application note SBAA094, Combining the ADS1202 with an FPGA Digital Filter for Current Measurement in Motor Control Applications, available for download at www.ti.com. 400 600 800 1000 Frequency (kHz) 1200 1400 1600 Figure 33. Frequency Response of Sinc3 Filter 30k In a Sinc3 filter response (shown in Figure 33 and OSR = 32 FSR = 32768 ENOB = 9.9 Bits Settling Time = 3 × 1/f DATA = 9.6µs 25k Output Code Figure 34), the location of the first notch occurs at the frequency of output data rate fDATA = fCLK/OSR. The –3dB point is located at half the Nyquist frequency or fDATA/4. For some applications, it may be necessary to use another filter type for better frequency response. 200 20k 15k 10k 5k 0 0 5 10 15 20 25 30 Number of Output Clocks 35 40 Figure 34. Pulse Response of Sinc3 Filter (fMOD = 10MHz) 17 www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 The effective number of bits (ENOB) can be used to compare the performance of ADCs and delta-sigma modulators. Figure 35 shows the ENOB of the ADS1205 with different filter types. In this data sheet, the ENOB is calculated from the SNR: SNR = 1.76dB + 6.02dB × ENOB (3) filter types other than Sinc3 might be a better choice. A simple example is a Sinc2 filter. The Sincfast is a modified Sinc2 filter: ǒ Ǔ 2 −OSR H(z) + 1 * z −1 ǒ1 ) z −2 1*z Ǔ OSR (4) Figure 36 compares the settling time of different filter types operating with a 10MHz modulator clock. 16 Sinc3 14 10 10 8 8 7 6 Sinc Sincfast Sinc3 9 Sinc2 ENOB (Bits) ENOB (Bits) 12 4 2 Sincfast Sinc2 6 5 Sinc 4 3 0 2 1 10 100 1000 OSR 1 0 Figure 35. Measured ENOB vs OSR In motor control applications, a very fast response time for overcurrent detection is required. There is a constraint between 1µs and 5µs with 3 bits to 7 bits resolution. The time for full settling is dependent on the filter order. Therefore, the full settling of the Sinc3 filter needs three data clocks and the Sinc2 filter needs two data clocks. The data clock is equal to the modulator clock divided by the OSR. For overcurrent protection, 18 0 2 4 6 8 10 Settling Time (µs) Figure 36. Measured ENOB vs Settling Time For more information, see application note SBAA094, Combining the ADS1202 with an FPGA Digital Filter for Current Measurement in Motor Control Applications, available for download at www.ti.com. www.ti.com SBAS312A − JANUARY 2005 − REVISED APRIL 2005 LAYOUT CONSIDERATIONS POWER SUPPLIES An applied external digital filter rejects high-frequency noise. PSRR and CMRR improve at higher frequencies because the digital filter suppresses high-frequency noise. However, the suppression of the filter is not infinite, so high-frequency noise still influences the conversion result. For multiple converters, connect the two ground planes as close as possible to one central location for all of the converters. In some cases, experimentation may be required to find the best point to connect the two planes together. DECOUPLING Inputs to the ADS1205, such as CH x+, CH x−, and CLKIN, should not be present before the power supply is on. Violating this condition could cause latch-up. If these signals are present before the supply is on, series resistors should be used to limit the input current to a maximum of 10mA. Experimentation may be the best way to determine the appropriate connection between the ADS1205 and different power supplies. Good decoupling practices must be used for the ADS1205 and for all components in the design. All decoupling capacitors, specifically the 0.1µF ceramic capacitors, must be placed as close as possible to the pin being decoupled. A 1µF and 10µF capacitor, in parallel with the 0.1µF ceramic capacitor, can be used to decouple AVDD to AGND as well as BVDD to BGND. At least one 0.1µF ceramic capacitor must be used to decouple every AVDD to AGND and BVDD to BGND, as well as for the digital supply on each digital component. GROUNDING The digital supply sets the I/O voltage for the interface and can be set within a range of 2.7V to 5.5V. Analog and digital sections of the design must be carefully and cleanly partitioned. Each section should have its own ground plane with no overlap between them. Do not join the ground planes; instead, connect the two with a moderate signal trace underneath the converter. However, for different applications with DSPs and switching power supplies, this process might be different. In cases where both the analog and digital I/O supplies share the same supply source, an RC filter of 10Ω and 0.1µF can be used to help reduce the noise in the analog supply. 19 PACKAGE OPTION ADDENDUM www.ti.com 21-Jun-2005 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty ADS1205IRGER ACTIVE QFN RGE 24 3000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR ADS1205IRGERG4 ACTIVE QFN RGE 24 3000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR ADS1205IRGET ACTIVE QFN RGE 24 250 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR ADS1205IRGETG4 ACTIVE QFN RGE 24 250 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR Lead/Ball Finish MSL Peak Temp (3) (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS) or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. 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