® SP8528 Micropower Sampling 12-Bit A/D Converter ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Low Cost 12-Bit Serial Sampling ADC Guaranteed +1.0 LSB Max INL Guaranteed No Missing Codes 8-Pin NSOIC Plastic Package Low Power @ 230µA including Automatic Shutdown: 1nA (typ) Full differential input stage Single Supply 3.0V to 5.5V operation Half Duplex Digital Serial Interface Sample Rate: 30.12µS Pin Compatible Upgrade to LTC 1286 DESCRIPTION The SP8528 is a very low power 12-Bit A/D converter. The SP8528 typically draws 230µA of supply current when sampling at 33.2 kHz. Supply current drops linearly as the sample rate is reduced. The ADC automatically powers down when not performing conversions, drawing only leakage current. The SP8528 is available in 8-Pin NSOIC packages, specified over Commercial and Industrial temperature ranges. The SP8528 is best suited for Battery-Operated Systems, Portable Data Acquisition Instrumentation, Battery Monitoring, and Remote Sensing applications. The serial port allows efficient data transfer to a wide range of microprocessors and microcontrollers over 3 wires. VCC GND Internal VCC REFL 12 REFL VREF DAC Csample P +IN INPUT SWITCHES COMPARATOR SAR PARALLEL TO SERIAL SHIFT REGISTER Dout -IN Csample N CS/SHDN TIMING & CONTROL LOGIC SCLK SP8528 Block Diagram SP8528DS/01 SP8528 Micropower Sampling 12-Bit A/D Converter 1 © Copyright 2000 Sipex Corporation ABSOLUTE MAXIMUM RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. (TA=+25˚C unless otherwise noted) ..................................................... VCC to GND ................................................................................. 7.0V Vin to GND .............................................................. -0.3 to VCC +0.3V Digital input to GND ................................................ -0.3 to VCC +0.3V Digital output to GND .............................................. -0.3 to VCC +0.3V Operating Temperature Range Commercial (J, K Version) ........................................... 0˚C to 70˚C Industrial (A, B Version) .......................................... -40˚C to +85˚C Lead Temperature (Solder 10Sec) ............................................ +300˚C Storage Temperature .................................................. -65˚C to +150˚C Power Dissipation to 70˚C ........................................................ 500mW SPECIFICATIONS Unless otherwise noted the following specifications apply for VCC=5V or 3.3V with limits applicable for Tmin to Tmax. Typical applies for Ta=25˚C. PARAMETERS DC ACCURACY Resolution Integral Linearity J,A K,B VCC=5.0V VCC=3.3V MIN. TYP. MAX. MIN. TYP. MAX. 12 12 UNITS Bits +0.6 +2.0 +0.6 +1.0 +0.6 +2.0 +0.6 +1.0 LSB LSB Differential Linearity Error J,A K,B +0.75 +2.0 +0.75 +1.0 +0.75 +2.0 +0.75 +1.0 LSB LSB Gain Error J,A K,B +2.0 +10 +2.0 +8 +2.0 +10 +2.0 +8 LSB LSB Offset Error J,A K,B +1.5 +1.5 +3.0 +3.0 LSB LSB ANALOG INPUT Input Signal FS Range Input Impedance On Channel Off Channel Input Bias Current Analog Input Range 0 +5 +3 Vref 0 20 100 3 100 .001 1 -.05 VCC+.05 -.05 20 100 3 100 .001 1 VCC+.05 pF MΩ pF MΩ µA Volts clock cycles clock cycles kHz µS µS µS 1.5 1.5 Conversion Time 12 12 SP8528DS/01 33.2 2.0 .9 .9 +8 +5 No Missing Codes Vref CONVERSION SPEED Sample Time Complete Cycle Clock Period Clock High Time Clock Low Time CONDITIONS 22.2 3.0 1.4 1.4 SP8528 Micropower Sampling 12-Bit A/D Converter 2 In Parallel with 100MΩ In Parallel with 100MΩ See Timing Diagrams See Timing Diagrams See Timing Diagrams See Timing Diagrams See Timing Diagrams See Timing Diagrams © Copyright 2000 Sipex Corporation SPECIFICATIONS (cont.) Unless otherwise noted the following specifications apply for VCC=5V or 3.3V with limits applicable for Tmin to Tmax. Typical applies for Ta=25˚C. PARAMETERS DIGITAL INPUTS Input Low Voltage, VIL Input High Voltage, VIH Input Current IIN Input Capacitance DIGITAL OUTPUTS Data Format Data Coding VOH VOL VCC=5.0V VCC=3.3V MIN. TYP. MAX. MIN. TYP. MAX. UNITS 0.8 2.0 0.8 2.0 +2.0 +2.0 3.0 3.0 4.0 2.0 0.4 0.4 Volts Volts µA pF Volts Volts AC ACCURACY Spurious free Dynamic Range (SFDR) 86 86 dB Total Harmonic Distortion (THD) -83 -80 dB Signal to Noise & Distortion (SINAD) 73 72 dB 73.5 72.5 dB Signal to Noise (SNR) SAMPLING DYNAMICS Acquisition Time to 0.01% -3dB Small Signal BW Aperture Delay Aperture Jitter Common-Mode Rejection Ratio POWER SUPPLIES VCC ICC 2 70 3 4 20 150 80 3 70 4.5 3 30 150 80 CONDITIONS VDD=5V +5% VDD=5V +5% See Timing Diagram VDD=5V ±5%, IOH=-0.4mA VDD=5V ±5%, IOL=+1.6mA For all FFT’s (Full Differential Mode) If VCC = 5V fsample = 31.25kHz fin = 15kHz If VCC = 3.3V fsample = 20.8kHz fin = 5kHz µs MHz nS pS dB fCM = 15kHz @ 5 volts 2.8kHz @ 3.3 volts Volts +3.0 +5.0 +5.5 +3.0 +3.3 +5.5 Operation Mode 230 400 80 300 µA (CS=0) 33.2kHz, 5V conversion rate. 22.2kHz 3.3 volts Shutdown Mode .001 0.5 .001 0.5 µA (CS=1) Power Dissipation Operating Mode Shutdown Mode 1.15 .005 2 10 0.26 0.99 .003 6.6 TEMPERATURE RANGE Commercial Industrial Storage SP8528DS/01 0˚ to +70˚C -40˚ to +85˚C -65˚ to +150˚C 0˚ to +70˚C -40˚ to +85˚C -65˚ to +150˚C mW µW ˚C ˚C ˚C SP8528 Micropower Sampling 12-Bit A/D Converter 3 © Copyright 2000 Sipex Corporation SPECIFICATIONS (cont.) Recommended Operating Conditions MIN. +3.0 VCC=5.0V TYP. MAX. +5.0 +5.5 PARAMETERS Supply Voltage fCLK Clock Frequency tCVC Total Cycle Time 30.1 45.15 µS tsuCS Setup Time CSv Before CLK^ 100 150 nS tWHCLK CLK High Time .9 1.4 µS TWHCLK CLK Low Time .9 1.4 µS TWHCS CS High Time between Data Transfers Cycles 100 150 nS 500 SP8528 GND 4 kHz Pin 1- VREF - Reference Voltage VREF 1 ▼ -IN 3 333 UNITS Volts PIN ASSIGNMENTS PIN DESCRIPTION +IN 2 MIN. +3.0 VCC=3.3V TYP. MAX. +3.3 +5.5 SYMBOL VCC 8 VCC 7 SCLK 6 DOUT 5 CS/SHDN Pin 2- +IN - Positive Input Pin 3- -IN - Negative Input Pin 4- GND - Ground Pin 5- CS/SHDN - Chip Select Bar/Shutdown Pin 6 - DOUT - Data Out Pin 7- SCLK - Serial Clock Pin 8- VCC - Supply SP8528DS/01 SP8528 Micropower Sampling 12-Bit A/D Converter 4 © Copyright 2000 Sipex Corporation DESCRIPTION The device features automatic shutdown and will shutdown to a +0.5 µA power level as CS is brought high (de-selected). Power is proportional to conversion duty cycle and varies from 230 µA at 30.1 µS (Duty cycle = 100%) to 5.75 µA at 1.2 ms (Duty cycle = 2.5%). The SP8528 is a 12 bit full differential sampling ADC with a serial data interface. The ADC samples and converts 12 bits of data in 30.1 µS with a 5V supply voltage applied. The SP8528 will also operate at a 3.3V supply at 45.15 µS throughput. The device automatically shuts down to a +0.5 µA (MAX) level as soon as the chip is deselected (CS=1). Serial data output is available in an MSB first or LSB first format. Examples: Conversion rate ICC @ 5V Duty Cycle 30.1 µS 230 µA 100% 60.2 µS 115 µA 50% 120 µS 57.5 µA 25% 1.20 mS 5.75 µA 2.5% The device can be configured such that it delivers serial data MSB first requiring 15 clock periods for a full conversion. Alternately, the device can be programmed to deliver 12 bits of data MSB first, followed by the same 12 bits of data LSB first. This sequence will require 26 clock periods to complete. Please refer to the timing diagram. FEATURES The input sampling scheme is full differential, where the maximum full scale range is VREF. The signal is applied between +IN and -IN. The signals applied at each input may both be dynamic. This is in contrast with pseudo differential devices which must have input low held at a constant level during conversion. The converter will provide significant common mode rejection because of the full differential sampling. Each input independently must remain between ground and Vcc to avoid clamping the inputs. For proper conversion the differential input (+IN - -IN) must be less than or equal to Vref. Circuit Operation The SP8528 is a SAR converter with full differential sampled front end, capacitive DAC, precision comparator, Successive Approximations Register, control logic and data output register. After the input is sampled and held the conversion process begins. The DAC MSB is set and its output is compared with the signal input, if the DAC output is less than the input, the comparator outputs a one which is latched into the SAR and simultaneously made available at the ADC serial output pin. Each bit is tested in a similar manner until the SAR contains a code which represents the signal input to within +1/2 LSB. During this process the SAR content has been shifted out of the ADC serially. If the MSB first format was chosen, the data will appear at the DOUT pin MSB through LSB in 15 clock periods. If LSB first data is desired, 26 SCLK’s are needed to complete a transfer. The LSB OUTPUT appears at clock 15, with CODE successive bits clocked out until the MSB appears at 000000000000 clock 26. All subsequent 000000000001 SCLK’s with CS = 0 shift out 100000000000 0. Note that the Chip Select 111111111110 Bar pin must be toggled high 111111111111 The device uses a capacitive DAC architecture which provides the sampling behavior. This results in full Nyquist performance at the fastest throughput rate (33.2kHz) the device is capable of. The power supply voltage is variable from 3.0V to 5.5V which provides supply flexibility. At the 5.0V supply level, conversion plus sampling time is 30.1 µS and supply current is 230 µA (1.15 mW). With a 3.3V supply the conversion plus sampling time is 45.15 µS and current is reduced to 80 µA (0.26 mW). ADC TRANSFER FUNCTION INPUT VOLTAGE (+IN - -IN) INPUT VOLTAGE AT VREF = 5V 0 LSB 1 LSB 2048 LSB 4094 LSB 4095 LSB 0V 0.00122V 2.5000V 4.9976V 4.9988V SP8528DS/01 SP8528 Micropower Sampling 12-Bit A/D Converter 5 © Copyright 2000 Sipex Corporation between conversions. The DOUT pin will be in a high impedance state whenever Chip Select Bar is high. After Chip Select Bar has been toggled and brought low again, the converter begins a new conversion. A circuit board layout which includes separate analog and digital ground planes will prevent the coupling of noise into sensitive converter circuits and will help to preserve the dynamic performance of the device. In single ended mode, the analog input signal should be referenced to the ground pin of the converter. This prevents any voltage drops that occur in the power supply's common return from appearing in series with the input signal. Single Ended or Full Differential Operation The SP8528 has a balanced full differential front end. The SP8528 can be used in this manner, or it can be used in single-ended circuits as well. For single-ended systems, simply tie the -IN to the Reference Low of the input signal, which is allowed to range from 0V to VCC. For a full differential sampling configuration, both inputs are sampled and held simultaneously. Because of the balanced differential sampling, dynamic common mode noise riding along the input signal is cancelled above and beyond DC noise. This is a significant improvement over psuedodifferential sampling schemes, where the low side of the input must remain constant during the conversion, and therefore only DC noise (i.e. signal offset) is cancelled. If AC common mode noise is left to be converted along with the differental component, the output signal will be degraded. In full differential mode, the high and low side board traces should run close to each other, with the same layout. This will insure that any noise coupling will be common mode, and cancelled by the converters (patent pending) full differential architecture. If separate analog and digital ground planes are not possible, care should be used to prevent coupling between analog and digital signals. If analog and digital lines must cross, they should do so at right angles. Parallel analog and digital lines should be separated by a circuit board trace which is connected to common. The reference pin on the SP8528 should be kept as clean as possible. A noise signal of 1.22mV (for VREF = 5.0V) will produce 1 lsb of error in the output code. For convenience, the VREF pin can be tied to the VCC pin, but now the same care should be taken with the VCC pin as with the VREF pin. Whether or not VCC is tied to VREF, the VCC pin should always be bypassed to the GROUND pin with a parallel combination of a 6.8µF tantalum and a 0.1µF ceramic capacitor. To maintain maximum system accuracy, the supply connected to the VCC pin should be well isolated from digital supplies and wide load variations. A separate conductor from the supply regulator to the A/D converter will limit the effects of digital switching elsewhere in the system. Power supply noise can degrade the converters performance. Especially corrupting are noise and spikes from a switching power supply. Full differential sampling allows flexibility in converting the input signal. If the signal lowside is already tied to a ground elsewhere in the system, it can be hardwired to the low side input (i.e., -IN) which acts as a signal ground sense, breaking a potential ground loop. It is also possible to drive the inputs balanced differential, as long as both inputs are within the power rails. In this configuration, both the high and low signals have the same impedance looking back to ground, and therefore pick up the same noise along the physical path from signal source (i.e., sensor, transducer, battery) to the converter. This noise becomes common mode, and is cancelled out by the differential sampling of the SP8528. Layout Considerations To preserve the high resolution and linearity of the SP8528 attention must be given to circuit board layout, ground impedance and bypassing. SP8528DS/01 To avoid introducing distortion when driving the A/D converter input, the input signal source should be able to charge the SP8528's equivalent 20 pF of input capacitance from zero volts to the signal level in 1.5 clock periods. SP8528 Micropower Sampling 12-Bit A/D Converter 6 © Copyright 2000 Sipex Corporation Tcyc POWER DOWN POWER UP PD PU Twhcs CSN 1 10 15 X X SCLK HI-Z Dout D11 D9 D7 D5 D3 D1 HI-Z 0 D10 D8 D6 D4 D2 D0 Tconv Tsample FIGURE 1. MSB FIRST TIMING Tcyc PD POWER UP POWER DOWN PU Twhcs CSN 1 SCLK Dout 15 10 20 25 26 X X HI-Z D11 D9 D7 D5 D3 D1 D1 D3 D5 D7 D9 D11 0 0 D10 D8 D6 D4 D2 D0 D2 D4 D6 D8 HI-Z D10 Tconv Tsample FIGURE 2. LSB FIRST TIMING Tsucs Tdis CSN Tscsu Ten Twhclk Twlclk Thdo Tclk SCLK Dout HI-Z Tf Tr 10% - 90% FIGURE 3. DETAILED TIMING SP8528 Timing Diagram SP8528DS/01 SP8528 Micropower Sampling 12-Bit A/D Converter 7 © Copyright 2000 Sipex Corporation Icc vs. Sampling Rate (Clock Rate = 333kHz) Vcc = 3.3V 90.0 Icc vs. Sampling Rate (Clock Rate = 500kHz) Vcc = 5V 250.0 80.0 200.0 60.0 50.0 Icc (µA) Icc (µA) 70.0 40.0 30.0 150.0 100.0 20.0 50.0 10.0 0.0 10 100 1000 10000 conversion time (µs) 0.0 100000 10 100 Vcc = 5V Vref = 5V 1000 10000 conversion time (µs) 100000 Vcc = 3.3V Vref = 3.3V +1 +1 INLE INLE -1 +1 -1 +1 DNLE DNLE -1 -1 0 4095 0 4095 Vcc = 5V Vref = 3V +1 Input CMRR Vcc = 5V 100 INLE CMRR (dB) 80 -1 +1 DNLE 60 40 20 0 10.0E+0 100.0E+0 1.0E+3 10.0E+3 100.0E+3 1.0E+6 common mode frequency(Hz) -1 0 SP8528DS/01 4095 SP8528 Micropower Sampling 12-Bit A/D Converter 8 © Copyright 2000 Sipex Corporation For all plots, VCC = 5V, Conversion Rate = 31.25kHz. Gain vs. Temperature Icc vs. Temperature 250 6.00 240 4.00 2.00 LSB µA 230 220 0.00 -2.00 210 -4.00 200 -50 -25 0 25 50 temperature (C) 75 100 -6.00 -50 125 -25 Offset vs. Temperature LSB 2 0 -2 0 -4 -25 0 25 50 75 temperature (C) 100 frequency SNR = 73.01 dB THD = -79.54 dB SINAD = 72.14 dB SFDR = 84.66 dB Vinamp = -0.47 dB 125 80 80 70 60 10000 input frequency (Hz) 60 50 1000 100000 10000 input frequency (Hz) 100000 Total Harmonic Distortion -50 80 -60 THD (dB) SNR (dB) Signal to Noise Ratio 70 60 10000 input frequency (Hz) 15.6kHz 70 90 SP8528DS/01 125 SINAD 90 SINAD (dB) SFDR (dB) Spurious Free Dynamic Range 90 50 1000 100 Spectral Density (dB) 4 50 1000 25 50 75 temperature (C) FFT 20 dB/div 6 -6 -50 0 -70 -80 -90 1000 100000 SP8528 Micropower Sampling 12-Bit A/D Converter 9 10000 input frequency (Hz) 100000 © Copyright 2000 Sipex Corporation PACKAGE: PLASTIC DUAL–IN–LINE (NARROW) E1 E D1 = 0.005" min. (0.127 min.) A1 = 0.015" min. (0.381min.) D A = 0.210" max. (5.334 max). C A2 L B1 B e = 0.100 BSC (2.540 BSC) Ø eA = 0.300 BSC (7.620 BSC) ALTERNATE END PINS (BOTH ENDS) DIMENSIONS (Inches) Minimum/Maximum (mm) 8–PIN 14–PIN 16–PIN 18–PIN 20–PIN 22–PIN A2 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) B 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) B1 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) C 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) D 0.355/0.400 0.735/0.775 0.780/0.800 0.880/0.920 0.980/1.060 1.145/1.155 (9.017/10.160) (18.669/19.685) (19.812/20.320) (22.352/23.368) (24.892/26.924) (29.083/29.337) E 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) E1 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) L 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) Ø 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) SP8528DS/01 SP8528 Micropower Sampling 12-Bit A/D Converter 10 © Copyright 2000 Sipex Corporation PACKAGE: PLASTIC SMALL OUTLINE (SOIC) (NARROW) E H h x 45° D A Ø e B A1 L DIMENSIONS (Inches) Minimum/Maximum (mm) SP8528DS/01 8–PIN 14–PIN 16–PIN A 0.053/0.069 (1.346/1.748) 0.053/0.069 (1.346/1.748) 0.053/0.069 (1.346/1.748) A1 0.004/0.010 (0.102/0.249 0.004/0.010 (0.102/0.249) 0.004/0.010 (0.102/0.249) B 0.014/0.019 (0.35/0.49) 0.013/0.020 (0.330/0.508) 0.013/0.020 (0.330/0.508) D 0.189/0.197 (4.80/5.00) 0.337/0.344 0.386/0.394 (8.552/8.748) (9.802/10.000) E 0.150/0.157 (3.802/3.988) 0.150/0.157 (3.802/3.988) 0.150/0.157 (3.802/3.988) e 0.050 BSC (1.270 BSC) 0.050 BSC (1.270 BSC) 0.050 BSC (1.270 BSC) H 0.228/0.244 (5.801/6.198) 0.228/0.244 (5.801/6.198) 0.228/0.244 (5.801/6.198) h 0.010/0.020 (0.254/0.498) 0.010/0.020 (0.254/0.498) 0.010/0.020 (0.254/0.498) L 0.016/0.050 (0.406/1.270) 0.016/0.050 (0.406/1.270) 0.016/0.050 (0.406/1.270) Ø 0°/8° (0°/8°) 0°/8° (0°/8°) 0°/8° (0°/8°) SP8528 Micropower Sampling 12-Bit A/D Converter 11 © Copyright 2000 Sipex Corporation ORDERING INFORMATION Model ........................................................ Linearity (LSB) ..................... Temperature Range ............................................................... Package SP8528BN .......................................................... ±1.0 .................................... –40˚C to +85˚C .............................................. 8-pin, 0.3" Plastic DIP SP8528KN .......................................................... ±1.0 ..................................... –0˚C to +70˚C ............................................... 8-pin, 0.3" Plastic DIP SP8528BS .......................................................... ±1.0 .................................... –40˚C to +85˚C ......................................... 8-pin, 0.15" Plastic SOIC SP8528KS .......................................................... ±1.0 ..................................... –0˚C to +70˚C .......................................... 8-pin, 0.15" Plastic SOIC SP8528AN .......................................................... ±2.0 .................................... –40˚C to +85˚C .............................................. 8-pin, 0.3" Plastic DIP SP8528JN ........................................................... ±2.0 ..................................... –0˚C to +70˚C ............................................... 8-pin, 0.3" Plastic DIP SP8528AS .......................................................... ±2.0 .................................... –40˚C to +85˚C ......................................... 8-pin, 0.15" Plastic SOIC SP8528JS ........................................................... ±2.0 ..................................... –0˚C to +70˚C .......................................... 8-pin, 0.15" Plastic SOIC Please consult the factory for pricing and availability on a Tape-On-Reel option. Corporation SIGNAL PROCESSING EXCELLENCE Sipex Corporation Headquarters and Sales Office 22 Linnell Circle Billerica, MA 01821 TEL: (978) 667-8700 FAX: (978) 670-9001 e-mail: [email protected] Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described hereing; neither does it convey any license under its patent rights nor the rights of others. SP8528DS/01 SP8528 Micropower Sampling 12-Bit A/D Converter 12 © Copyright 2000 Sipex Corporation