REV. 0Information furnished by Analog Devices is believed to be accurate andreliable. However, no responsibility is assumed by Analog Devices for itsuse, nor for any infringements of patents or other rights of third partieswhich may result from its use. No license is granted by implication orotherwise under any patent or patent rights of Analog Devices.aAD7862One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.Tel: 617/329-4700 World Wide Web Site: http://www.analog.comFax: 617/326-8703 © Analog Devices, Inc., 1996Simultaneous SamplingDual 250 kSPS 12-Bit ADCFUNCTIONAL BLOCK DIAGRAMCLOCKDGNDDB0BUSYRDCSCONVSTAD7862CONVERSIONCONTROL LOGICVA1AGNDVREF+2.5VREFERENCE2kΩAGNDTRACK/HOLDVDDDB11OUTPUTLATCHMUXA012-BITADC12-BITADCTRACK/HOLDMUXSIGNALSCALINGSIGNALSCALINGSIGNALSCALINGSIGNALSCALINGVB1VA2VB2FEATURESTwo Fast 12-Bit ADCsFour Input ChannelsSimultaneous Sampling & Conversion4 ms Throughput TimeSingle Supply OperationSelection of Input Ranges:610 V for AD7862-1062.5 V for AD7862-30 V to 2.5 V for AD7862-2High Speed Parallel InterfaceLow Power, 60 mW typPower Saving Mode, 50 mW typOvervoltage Protection on Analog Inputs14-Bit Pin Compatible Upgrade (AD7863)APPLICATIONSAC Motor ControlUninterrupted Power SuppliesData Acquisition SystemsCommunicationsGENERAL DESCRIPTIONThe AD7862 is a high speed, low power, dual 12-bit A/Dconverter that operates from a single +5 V supply. The partcontains two 4 µs successive approximation ADCs, two track/hold amplifiers, an internal +2.5 V reference and a high speedparallel interface. There are four analog inputs that are groupedinto two channels (A & B) selected by the A0 input. Eachchannel has two inputs (VA1 & VA2 or VB1 & VB2) that can besampled and converted simultaneously thus preserving therelative phase information of the signals on both analog inputs.The part accepts an analog input range of ±10 V (AD7862-10),±2.5 V (AD7862-3) and 0–2.5 V (AD7862-2). Overvoltageprotection on the analog inputs for the part allows the inputvoltage to go to ±17 V, ±7 V or +7 V, respectively, withoutcausing damage.A single conversion start signal (CONVST) places both track/holds into hold simultaneously and initiates conversion on bothinputs. The BUSY signal indicates the end of conversion, andat this time the conversion results for both channels are avail-able to be read. The first read after a conversion accesses theresult from VA1 or VB1, while the second read accesses the resultfrom VA2 or VB2, depending on whether the multiplexer selectA0 is low or high, respectively. Data is read from the part via a12-bit parallel data bus with standard CS and RD signals.In addition to the traditional dc accuracy specifications such aslinearity, full-scale and offset errors, the part is also specified fordynamic performance parameters including harmonic distortionand signal-to-noise ratio.The AD7862 is fabricated in Analog Devices’ Linear Compat-ible CMOS (LC2MOS) process, a mixed technology processthat combines precision bipolar circuits with low power CMOSlogic. It is available in 28-lead SSOP, SOIC and DIP.PRODUCT HIGHLIGHTS1. The AD7862 features two complete ADC functions allowingsimultaneous sampling and conversion of two channels. EachADC has a 2-channel input mux. The conversion result forboth channels is available 3.6 µs after initiating conversion.2. The AD7862 operates from a single +5 V supply andconsumes 60 mW typ. The automatic power-down mode,where the part goes into power down once conversion iscomplete and “wakes up” before the next conversion cycle,makes the AD7862 ideal for battery-powered or portableapplications.3. The part offers a high speed parallel interface for easy con-nection to microprocessors, microcontrollers and digitalsignal processors.4. The part is offered in three versions with different analoginput ranges. The AD7862-10 offers the standard industrialinput range of ±10 V; the AD7862-3 offers the commonsignal processing input range of ±2.5 V; while the AD7862-2can be used in unipolar 0 V – +2.5 V applications.5. The part features very tight aperture delay matching betweenthe two input sample-and-hold amplifiers.–2–REV. 0AD7862–SPECIFICATIONSAB SParameter Version1Version Version Units Test Conditions/CommentsSAMPLE AND HOLD–3 dB Small Signal Bandwidth 3 3 3 MHz typAperture Delay 20 20 20 ns typAperture Jitter 100 100 100 ps typAperture Delay Matching 200 200 200 ps typDYNAMIC PERFORMANCE2fIN = 100.0 kHz, fS = 250 kSPSSignal to (Noise+Distortion) Ratio3@ +25°C 70 71 70 dB minTMIN to TMAX70 70 70 dB minTotal Harmonic Distortion3–78 –78 –78 dB maxPeak Harmonic or Spurious Noise3–85 –85 –85 dB typIntermodulation Distortion3fa = 49 kHz, fb = 50 kHz2nd Order Terms –85 –85 –85 dB typ3rd Order Terms –85 –85 –85 dB typChannel to Channel Isolation3–80 –80 –80 dB max fIN = 100 kHz Sine WaveDC ACCURACY Any ChannelResolution 12 12 12 BitsMinimum Resolution for whichNo Missing Codes are Guaranteed 12 12 12 BitsRelative Accuracy3±1 ±1 ±1 LSB max Typically 0.4 LSBDifferential Nonlinearity3±1 ±1 ±1 LSB maxPositive Gain Error3±4 ±3 ±4 LSB maxPositive Gain Error Match34 3 4 LSB maxAD7862-10Negative Gain Error3±4 ±3 ±4 LSB maxBipolar Zero Error ±4 ±3 ±4 LSB maxBipolar Zero Error Match 4 3 4 LSB maxAD7862-3Negative Gain Error3±4 ±3 ±4 LSB maxBipolar Zero Error ±4 ±3 ±4 LSB maxBipolar Zero Error Match 4 3 4 LSB maxAD7862-2Unipolar Offset Error +4 +3 +4 LSB maxUnipolar Offset Error Match 4 3.5 4 LSB maxANALOG INPUTSAD7862-10Input Voltage Range ±10 ±10 ±10 Volts InputInput Resistance 24 24 24 kΩ minAD7862-3Input Voltage Range ±2.5 ±2.5 ±2.5 Volts InputInput Resistance 6 6 6 kΩ minAD7862-2Input Voltage Range +2.5 +2.5 +2.5 Volts InputInput Current 500 500 500 nA maxREFERENCE INPUT/OUTPUTREF IN Input Voltage Range 2.375/2.625 2.375/2.625 2.375/2.625 V min/V max 2.5 V ± 5%REF IN Input Capacitance410 10 10 pF maxREF OUT Output Voltage 2.5 2.5 2.5 V nomREF OUT Error @ +25°C ±10 ±10 ±10 mV maxREF OUT Error TMIN to TMAX±25 ±25 ±25 mV maxREF OUT Temperature Coefficient 25 25 25 ppm/°C typREF OUT Output Impedance 2 2 2 kΩ nomLOGIC INPUTSInput High Voltage, VINH2.4 2.4 2.4 V min VDD = 5 V ± 5%Input Low Voltage, VINL0.8 0.8 0.8 V max VDD = 5 V ± 5%Input Current, IIN±10 ±10 ±10 µA maxInput Capacitance, CIN410 10 10 pF max(VDD = +5 V 6 5%, AGND = DGND = 0 V, REF = Internal. All Specifications TMIN to TMAXunless otherwise noted.)–3–REV. 0AD7862AB SParameter