ANALOG DEVICES AD7816/AD7817/AD7818 handbook
Contents
1. 0 AD7816ACHIPS 0 ANALOG DEVICES Single and 4 Channel 9 ps 10 Bit ADCs with On Chip Temperature Sensor AD7816 AD7817 AD7818 FEATURES 10 Bit ADC with 9 ws Conversion Time One AD7818 and Four AD7817 Single Ended Analog Input Channels The AD7816 Is a Temperature Measurement Only Device On Chip Temperature Sensor Resolution of 0 25 C 2 C Error from 40 C to 85 C 55 C to 125 C Operating Range Wide Operating Supply Range 2 7 V to 5 5 V Inherent Track and Hold Functionality On Chip Reference 2 5 V 1 Overtemperature Indicator Automatic Power Down at the End of a Conversion Low Power Operation 4 pW at a Throughput Rate of 10 SPS 40 pW at a Throughput Rate of 1 kSPS 400 at a Throughput Rate of 10 kSPS Flexible Serial Interface APPLICATIONS Ambient Temperature Monitoring AD7816 Thermostat and Fan Control High Speed Microprocessor Temperature Measurement and Control Data Acquisition Systems with Ambient Temperature Monitoring AD7817 and AD7818 Industrial Process Control Automotive Battery Charging Applications GENERAL DESCRIPTION The AD7818 and AD7817 are 10 bit single and 4 channel A D converters with on chip temperature sensor that can oper ate from a single 2 7 V to 5 5 V power supply Each part con tains a 9 us successive approximation converter based around a capacitor DAC an on chip temperature sensor with an accu racy of 2 C an on chip clock oscillator inherent track and2. age TSSOP while the AD7816 AD7818 come in an 8 lead small outline IC SOIC and an 8 lead microsmall outline IC MSOP PRODUCT HIGHLIGHTS 1 The devices have an on chip temperature sensor that allows an accurate measurement of the ambient temperature to be made The measurable temperature range is 55 C to 125 An overtemperature indicator is implemented by carrying out a digital comparison of the ADC code for Channel 0 tempera ture sensor with the contents of the on chip overtemperature register The overtemperature indicator pin goes logic low when a predetermined temperature is exceeded The automatic power down feature enables the AD7816 AD7817 and AD7818 to achieve superior power perfor mance at slower throughput rates e g 40 uW at 1 kSPS throughput rate One Technology Way P O Box 9106 Norwood MA 02062 9106 U S A Tel 781 329 4700 www analog com Fax 781 326 8703 2004 Analog Devices Inc All rights reserved AD7816 AD7817 AD7818 AD7817 SPECIFICATIONS Voo 2 7 V to 5 5 V GND 0 V REF y 2 5 V unless otherwise noted Parameter A Version B Version S Version Unit Test Conditions Comments DYNAMIC PERFORMANCE Sample Rate 100 kSPS Any Channel f 20 kHz Signal to Noise Distortion Ratio 58 58 58 dB min Total Harmonic Distortion 65 65 65 dB max 15 dB typ Peak Harmonic or Spurious Noise 65 65 65 dB max 15 dB
3. ABSOLUTE MAXIMUM RATINGS T4 25 C unless otherwise noted tO AGND ret 0 3 V to 7 V Vip to DGND RR EV Car x s xe 0 3 V to 7 V Analog Input Voltage to AGND Vini tO Vind e e E eae 0 3 V to Vpp 0 3 V Reference Input Voltage to AGND 0 3 V to Vpp 0 3 V Digital Input Voltage to DGND 0 3 V to Vpp 0 3 V Digital Output Voltage to DGND 0 3 V to Vpp 0 3 V Storage Temperature Range 65 to 150 C Junction Temperature 4 scence eee e wee 150 C TSSOP Power Dissipation 450 mW 0j Thermal Impedance 120 C W Lead Temperature Soldering 260 C Vapor Phase 60 sec 215 C Infrared 15 sec 220 C 16 Lead SOIC Package Power Dissipation 450 mW 0j Thermal Impedance 100 C W Lead Temperature Soldering Vapor Phase 60 seC osse ee 215 C Infrared LI Sec 3 24 5 ches th RE e thd 220 C 8 Lead SOIC Package Power Dissipation 450 mW Oja Thermal Impedance 157 C W Lead Temperature Soldering Vapor Phase 60 sec 215 C Infrared 15 i e eisai area Ev 220 C uSOIC Package Power Dissipation 450 mW Oja Thermal Impedance 206 C W Lead Temperature Soldering Vapor Phase 60 sec 215 C Infrared 15 SEC
4. 2 ce ea bh S ER 220 C NOTES Stresses above those listed under Absolute Maximum Ratings may cause perma nent damage to the device This is a stress rating only functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied Exposure to absolute maximum rating condi tions for extended periods may affect device reliability 21 the Reference Input Voltage is likely to exceed Vpp by more than 0 3 V e g during power up and the reference is capable of supplying 30 mA or more it is recommended to use a clamping diode between the REF pin and Vpp pin The diagram below shows how the diode should be connected REF iy AD7816 AD7817 REV AD7816 AD7817 AD7818 ORDERING GUIDE Temperature Temperature Package Package Model Range Error 25 C Description Options Branding AD7816AR 40 C to 85 C X22 8 Lead Narrow Body SOIC R 8 AD7816AR REEL 40 C to 85 C X2 C 8 Lead Narrow Body SOIC R 8 AD7816AR REEL7 40 C to 85 C 2 C 8 Lead Narrow Body SOIC R 8 AD7816ARM 40 C to 85 C 2 8 Lead MSOP RM 8 C4A AD7816ARM REEL 40 C to 85 C 2 8 Lead MSOP RM 8 C4A AD7816ARM REEL7 40 C to 85 C 2 8 Lead MSOP RM 8 C4A AD7816ACHIPS Die AD7817AR 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD7817AR REEL 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD781
5. 201og V GND 3 Not to Scale 6 Diyour a sly where V is the rms amplitude of the fundamental and V2 V3 ii x V4 Vs and Vg are the rms amplitudes of the second through the sixth harmonics SOIC MSOP AD7818 Peak Harmonic or Spurious Noise Peak harmonic or spurious noise is defined as the ratio of the CONVST 1 e 8 RD WR rms value of the next largest component in the ADC output 2 07818 SCLK spectrum up to amp 2 and excluding dc to the rms value of the GND 3 Not to Scale 6 Diuour fundamental Normally the value of this specification is deter Vin 5 voo mined by the largest harmonic in the spectrum but for parts where the harmonics are buried in the noise floor it will be a noise peak TERMINOLOGY Intermodulation Distortion Signal to Noise Distortion Ratio This is the measured ratio of signal to noise distortion at the output of the A D converter The signal is the rms amplitude of the fundamental Noise is the rms sum of all nonfundamental signals up to half the sampling frequency 6 2 excluding The ratio is dependent upon the number of quantization levels in the digitization process the more levels the smaller the quantiza tion noise The theoretical signal to noise distortion ratio for an ideal N bit converter with a sine wave input is given by Signal to Noise Distortion 6 02 N 1 76 dB Thus for a 10 bit converter this is 62 dB REV With inputs consisting of sine wa
6. hold functionality and an on chip reference 2 5 V The AD7816 is a temperature monitoring only device in a SOIC MSOP package The on chip temperature sensor of the AD7817 and AD7818 can be accessed via Channel 0 When Channel 0 is selected and a conversion is initiated the resulting ADC code at the end of the conversion gives a measurement of the ambient temperature with a resolution of 0 25 C See Temperature Measurement section of this data sheet REV C Information furnished by Analog Devices is believed to be accurate and reliable However no responsibility is assumed by Analog Devices for its use norfor any infringements of patents or other rights ofthird parties that may result from its use No license is granted by implication or otherwise under any patent or patent rights of Analog Devices Trademarks and registered trademarks are the property of their respective owners FUNCTIONAL BLOCK DIAGRAM REF iy Vpp TEMP SENSOR SAMPLING CAPACITOR AGND DGND BUSY CONVST The AD7816 AD7817 and AD7818 have a flexible serial interface that allows easy interfacing to most microcontrollers The interface is compatible with the Intel 8051 Motorola SPI and QSPI protocols and National Semiconductors MICROWIRE protocol For more information refer to the Serial Interface section of this data sheet The AD7817 is available in a narrow body 0 15 16 lead small outline IC SOIC in a 16 lead thin shrink small outline pack
7. 1001 1100 0 C 10 0000 0000 25 C 10 0111 1000 55 11 1001 0000 125 C TEMPERATURE MEASUREMENT ERROR DUE TO REFERENCE ERROR The AD7816 AD7817 and AD7818 are trimmed using a pre cision 2 5 V reference to give the transfer function described previously To show the effect of the reference tolerance on a temperature reading the temperature sensor transfer function can be rewritten as a function of the reference voltage and the temperature CODE Dec 113 3285 x K x T q Vggr 0 6646 x 1024 where Boltzmann s Constant 1 38 x 107 q Charge on an electron 1 6 x 10 T Temperature K So for example to calculate the ADC code at 25 C CODE 113 3285 x 298 x 1 38 x 10 7 1 6 x 10 x2 5 0 6646 x 1024 511 5 200 Hex As can be seen from the expression a reference error will pro duce a gain error This means that the temperature measure ment error due to reference error will be greater at higher temperatures For example with a reference error of 196 the measurement error at 55 C would be 2 2 LSBs 0 5 C and 16 LSBs 4 C at 125 C SELF HEATING CONSIDERATIONS The AD7817 and AD7818 have an analog to digital conversion function capable of a throughput rate of 100 kSPS At this throughput rate the AD7817 and AD7818 will consume between 4 mW and 6 5 mW of power Because a thermal impedance is associated with the IC package the temperature of the die will rise as a result o
8. 4LAYERPCB TEMPERATURE C TIME secs Figure 13 Self Heating Effect Two Layer and Four Layer PCB 43 gt AD7816 AD7817 AD7818 0 8 0 7 gt 0 6 0 5 0 4 0 3 0 2 f 0 1 TEMPERATURE C 0 0 0 01 0 2 4 6 8 10 12 14 16 TIME secs Figure 14 Self Heating Effect in Air Fluid and in Thermal Contact with a Heat Sink 0 25 0 20 0 15 0 10 0 05 TEMPERATURE C 0 00 lt 0 0 0 5 1 0 1 5 2 0 TIME secs Figure 15 Self Heating Effect in Air Fluid and in Thermal Contact with a Heat Sink cs tis OPERATING MODES The AD7816 AD7817 and AD7818 have two possible modes of operation depending on the state of the CONVST pulse at the end of a conversion Mode 1 In this mode of operation the CONVST pulse is brought high before the end of a conversion i e before the BUSY goes low see Figure 16 When operating in this mode a new conversion should not be initiated until 100 ns after the end of a serial read operation This quiet time is to allow the track hold to accu rately acquire the input signal after a serial read Mode 2 When the AD7816 AD7817 and AD7818 are operated in Mode 2 see Figure 17 they automatically power down at the end of a conversion The CONVST is brought low to initiate a conver sion and is left logic low until after the end of the conversion At t
9. 7AR REEL7 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD7817ARZ 40 C to 85 C 2 16 Narrow Body SOIC R 16 AD7817ARU 40 C to 85 C 2 C 16 Lead TSSOP RU 16 AD7817ARU REEL 40 C to 85 C 2 16 Lead TSSOP RU 16 AD7817ARU REEL7 40 C to 85 C 2 16 Lead TSSOP RU 16 AD7817BR 40 C to 85 C 1 C 16 Lead Narrow Body SOIC R 16 AD7817BR REEL 40 C to 85 C 1 C 16 Lead Narrow Body SOIC R 16 AD7817BR REEL7 40 C to 85 C 1 C 16 Lead Narrow Body SOIC R 16 AD7817BRZ 40 C to 85 C 1 C 16 Lead Narrow Body SOIC R 16 AD7817BRZ REEL 40 C to 85 C 1 C 16 Lead Narrow Body SOIC R 16 AD7817BRZ REEL7 40 C to 85 C 1 C 16 Lead Narrow Body SOIC R 16 AD7817BRU 40 C to 85 C 1 C 16 Lead TSSOP RU 16 AD7817BRU REEL 40 C to 85 1 C 16 Lead TSSOP RU 16 AD7817BRU REEL7 40 C to 85 C 1 C 16 Lead TSSOP RU 16 AD7817SR 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD7817SR REEL 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD7817SR REEL7 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD7818AR 40 C to 85 C 2 C 16 Lead Narrow Body SOIC R 16 AD7818AR REEL 40 C to 85 C 2 8 Lead Narrow Body SOIC R 8 AD7818AR REEL7 40 C to 85 C 2 C 8 Lead Narrow Body SOIC R 8 AD7818ARM 40 C to 85 C 2 C 8 Lead MSOP RM 8 C3A AD7818ARM REEL 40 C to 85 C 2 8 Lead MS
10. ARE WRITTEN TO THE OVERTEMPERATURE REGISTER 087 006 pes 064 nes mes 061 peo OVERTEMPERATURE Figure 4 Address and Overtemperature Register Selection REV AD7816 AD7817 AD7818 OVERTEMPERATURE REGISTER M 0 0 0 0 1 1 1 1 1 1 OVERTEMPERATURE REGISTER DEC Tai 103 C RESOLUTION 1 LSB SB LSB osr ses 000 00 oma om oeo MINIMUM TEMPERATURE 95 MAXIMUM TEMPERATURE 152 C 0 0 1 1 Figure 5 The Overtemperature Register OTR CIRCUIT INFORMATION The AD7817 and AD7818 are single and four channel 9 us conversion time 10 bit A D converters with on chip tempera ture sensor reference and serial interface logic functions on a single chip The AD7816 has no analog input channel and is intended for temperature measurement only The A D converter section consists of a conventional successive approximation converter based around a capacitor DAC The AD7816 AD7817 and AD7818 are capable of running on a 2 7 V to 5 5 V power supply and the AD7817 and AD7818 accept an analog input range of 0 V to Vpgp The on chip temperature sensor allows an accurate measurement of the ambient device temperature to be made The working measurement range of the temperature sensor is 55 C to 125 C The part requires 2 5 V reference which can be provided from the part s own internal reference or from an external reference source The on chip reference is select
11. Capacitance 10 10 10 pF max LOGIC INPUTS Input High Voltage Ving 2 4 2 4 2 4 V min Vpp 5V 10 Input Low Voltage Vint 0 8 0 8 0 8 V max Vpp 5 V 10 Input High Voltage Ving 2 2 2 V min Vpp 3 V 10 Input Low Voltage Vint 0 4 0 4 0 4 V max Vpp 3 V 10 Input Current In 3 3 3 uA max Typically 10 nA Vw 0 V to Vpp Input Capacitance Cr 10 10 10 pF max LOGIC OUTPUTS Output High Voltage Voy Tsource 200 HA 4 4 4 V min Vpp 5 V 10 2 4 2 4 2 4 V min Vpp 3 V 10 Output Low Voltage VoL Ismk 200 uA 0 4 0 4 0 4 V max Vpp 5 V 10 0 2 0 2 0 2 V max Vpp 3 V 10 High Impedance Leakage Current 1 sel 1 uA max High Impedance Capacitance 15 15 15 pF max NOTES B and S Versions apply to AD7817 only For operating temperature ranges see Ordering Guide 1AD7816 and AD7817 temperature sensors specified with external 2 5 V reference AD7818 specified with on chip reference All other specifications with external and on chip reference 2 5 V For Vpp 2 7 V T4 85 C max and temperature sensor measurement error 3 C See Terminology 3The accuracy of the temperature sensor is affected by reference tolerance The relationship between the two is explained in the section titled Temperature Measure ment Error Due to Reference Error Sample tested during initial release and after any redesign or process change that may affect this parameter 5On chip reference shuts down when external reference i
12. D WR or on the rising edge of the CS signal whichever occurs first Logic Input Data is clocked into the AD7817 at this pin Clock Input for the Serial Port The serial clock is used to clock data into and out of the AD7817 Data is clocked out on the falling edge and clocked in on the rising edge Logic Input Signal The read write signal is used to indicate to the AD7817 whether the data transfer operation is a read or a write The RD WR should be set logic high for a read operation and logic low for PIN CONFIGURATION SOIC TSSOP CONVST 1 e 16 RD WR cs a AD7817 3 Dour TOP VIEW AGND 5 Not to Scale 12 8 REV AD7816 AD7817 AD7818 AD7816 AND AD7818 PIN FUNCTION DESCRIPTIONS Pin Mnemonic Description 1 CONVST 2 OTI 3 GND 4 AD7818 Vin Analog and Digital Ground Logic Input Signal The convert start signal initiates a 10 bit analog to digital conversion on the falling edge of the this signal The falling edge of this signal places the track hold in hold mode The track hold goes into track mode again at the end of the conversion The state of the CONVST signal is checked at the end of a conversion If it is logic low the AD7816 and AD7818 will power down see Operating Mode section of the data sheet Logic Output The Overtemperature Indicator OTD is set logic low if the result of a conversion on Channel 0 Temperature Sensor is greater that an 8 bit word in the Overtemperatur
13. EFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN 16 Lead Standard Small Outline Package SOIC Narrow Body R 16 Dimensions shown in millimeters and inches 10 00 0 3937 E 9 80 0 3858 4 00 0 1575 6 20 0 2441 3 80 0 1496 5 80 0 2283 Te D DE OB 1 27 0 0500 1 75 0 0689 0 50 0 0197 BSC 1 35 0 0531 7625 0 0088 45 t 0 25 0 0098 0 1 27 0 0500 0 17 0 0067 0 40 0 0157 0 25 0 0098 0 10 0 0039 0 j 114 0 51 0 0201 SEATING COPLANARITY plied Sect 9 0 31 0 0122 PLANE 0 10 COMPLIANT TO JEDEC STANDARDS MS 012AC CONTROLLING DIMENSIONS ARE IN MILLIMETERS INCH DIMENSIONS IN PARENTHESES ARE ROUNDED OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN REV C 17 8 Lead Mini Small Outline Package MSOP RM 8 Dimensions shown in millimeters 0 15 1 10 MAX 6 00 Y 0 80 4 oae o23 4 8 gt b 0 60 0 22 0 08 0 40 COPLANARITY SEATING 0 10 PLANE COMPLIANT TO JEDEC STANDARDS MO 187AA 16 Lead Thin Shrink Small Outline Package TSSOP RU 16 Dimensions shown in millimeters 0 15 0 20 Ge 124 s Hoe nm BSC 0 19 SEATING 035 copLanaRiTy PLANE 0 10 COMPLIANT TO JEDEC STANDARDS MO 153AB AD7816 AD7817 AD7818 Revision History Location Page 9104 Data Sheet changed from REV B to REV C Update
14. NSFER FUNCTION The output coding of the AD7816 AD7817 and AD7818 is straight binary The designed code transitions occur at succes sive integer LSB values i e 1 LSB 2 LSBs etc The LSB size is 2 5 V 1024 2 44 mV The ideal transfer characteristic is shown in Figure 10 below 111 111 111 110 e 4 e 111 000 e vA 1LSB 2 5 1024 e 2 44mV 011 111 e 000 010 000 001 000 000 S gt 1LSB 42 5V 1LSB ANALOG INPUT Figure 10 ADC Transfer Function ADC CODE TEMPERATURE MEASUREMENT The on chip temperature sensor can be accessed via multiplexer Channel 0 i e by writing 0 0 0 to the channel address register The temperature is also the power on default selection The transfer characteristic of the temperature sensor is shown in Figure 11 below The result of the 10 bit conversion on Chan nel 0 can be converted to degrees centigrade by using the fol lowing equation Tams 103 C ADC Code 4 TEMPERATURE 55 C T gt 192Dec ADC CODE 912Dec Figure 11 Temperature Sensor Transfer Characteristic REV For example if the result of a conversion on Channel 0 was 1000000000 512 Dec the ambient temperature is equal to 103 512 4 25 Table II below shows some ADC codes for various temperatures Table II Temperature Sensor Output ADC Code Temperature 00 1100 0000 55 C 01 0011 1000 25 C 01
15. OP RM 8 C3A AD7818ARM REEL7 40 C to 85 C 2 8 Lead MSOP RM 8 C3A EVAL AD7816 Evaluation Board AD7817 AD7818EB Z Pb free part CAUTION ESD electrostatic discharge sensitive device Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection Although the AD7816 AD7817 AD7818 features proprietary ESD protection circuitry permanent damage may occur on devices subjected to high energy electrostatic discharges Therefore proper ESD precautions are recommended to avoid performance degradation or loss of functionality REV WARNING ESD A SENSITIVE DEVICE AD7816 AD7817 AD7818 AD7817 PIN FUNCTION DESCRIPTIONS Pin Mnemonic Description 1 CONVST Logic Input Signal The convert start signal A 10 bit analog to digital conversion is initiated on the falling edge of this signal The falling edge of this signal places the track hold in hold mode The track hold goes into track mode again at the end of the conversion The state of the CONVST signal is checked at the end of a conversion If it is logic low the AD7817 will power down see Operating Mode section of the data sheet 2 BUSY Logic Output The busy signal is logic high during a temperature or voltage A D conversion The signal can be used to interrupt a microcontroller when a conversion has finished 3 OTI Logic Output The Overtemperature Indicator
16. OTI is set logic low if the result of a conversion on Channel 0 Temperature Sensor is greater that an 8 bit word in the Overtemperature Register OTR The signal is reset at the end of a serial read operation i e a rising RD WR edge when CS is low 4 CS Logic Input Signal The chip select signal is used to enable the serial port of the AD7817 This is neces sary if the AD7817 is sharing the serial bus with more than one device 5 AGND Analog Ground Ground reference for track hold comparator and capacitor DAC 6 REF Analog Input An external 2 5 V reference can be connected to the AD7817 at this pin To enable the on 7 10 to Vina Byte section 11 Vpp 12 DGND 13 Dour 14 Dn 15 SCLK 16 RD WR a write operation chip reference the REFy pin should be tied to AGND If an external reference is connected to the AD7817 the internal reference will shut down Analog Input Channels The AD7817 has four analog input channels The input channels are single ended with respect to AGND analog ground The input channels can convert voltage signals in the range 0 V to A channel is selected by writing to the Address Register of the AD7817 see Control Positive Supply Voltage 2 7 V to 5 5 V Digital Ground Ground reference for digital circuitry Logic Output With a High Impedance State Data is clocked out of the AD7817 serial port at this pin This output goes into a high impedance state on the falling edge of R
17. SB of its final value The time it takes to charge the sampling capacitor Tcyarcg is given by the following formula T CHARGE 7 6 X R2 1 RQ x 3 pF For small values of source impedance the settling time associ ated with the sampling circuit 100 ns is in effect the acquisi tion time of the ADC For example with a source impedance R2 of 10 Q the charge time for the sampling capacitor is approxi mately 23 ns The charge time becomes significant for source impedances of 1 kO and greater AC Acquisition Time In ac applications it is recommended to always buffer analog input signals The source impedance of the drive circuitry must be kept as low as possible to minimize the acquisition time of the ADC Large values of source impedance will cause the THD to degrade at high throughput rates ON CHIP REFERENCE The AD7816 AD7817 and AD7818 have an on chip 1 2 V band gap reference that is gained up to give an output of 2 5 V The on chip reference is selected by connecting the REFyy pin to analog ground This causes 571 see Figure 9 to open and the reference amplifier to power up during a conversion There fore the on chip reference is not available externally An external 2 5 V reference can be connected to REFy pin This has the effect of shutting down the on chip reference circuitry and reduc ing Ipp by about 0 25 mA 2 REF iy EXTERNAL REFERENCE DETECT BUFFER Figure 9 On Chip Reference ADC TRA
18. The maximum current these diodes can conduct without causing irreversible damage to the part is 20 mA The capacitor C2 in Figure 7 is typically about 4 pF and can mostly be attributed to pin capacitance The resistor R1 is a lumped component made up of the on resistance of a multiplexer and a switch This resistor is typically about 1 KQ The capacitor C1 is the ADC sampling capacitor and has a capacitance of 3 pF 11 AD7816 AD7817 AD7818 Vpp D1 R1 c1 1kQ 3pF An O0 NW 1 veac c2 D2 CONVERT PHASE SWITCH OPEN TRACK PHASE SWITCH CLOSED Figure 7 Equivalent Analog Input Circuit DC Acquisition Time The ADC starts a new acquisition phase at the end of a conver sion and ends on the falling edge of the CONVST signal At the end of a conversion a settling time is associated with the sam pling circuit This settling time lasts approximately 100 ns The analog signal Vy is also being acquired during this settling time Therefore the minimum acquisition time needed is approximately 100 ns Figure 8 shows the equivalent charging circuit for the sampling capacitor when the ADC is in its acquisition phase R2 repre sents the source impedance of a buffer amplifier or resistive network R1 is an internal multiplexer resistance and C1 is the sampling capacitor R1 Vin 1kQ Y Figure 8 Equivalent Sampling Circuit During the acquisition phase the sampling capacitor must be charged to within a 1 2 L
19. d ORDERING GUIDE arg NE genie ash E E E pe ERU UR As 6 Changes to Operating Modes section lisse eed EO Seared ce VU e ed ad ee 13 Changes to Figure prep ek dre eee oe oe p 13 Changes Se ee d Deas aive dede Sateen Sd Grae 14 Changes to AD7817 Serial Interface Read Operation section 2 0 0 hh m hn 15 Changes tO Figure 20550502 suns db en ente de 15 hb SEORSIM 16 18 REV 19 3 70 6 0 9 LELOD 20
20. e Register OTR The signal is reset at the end of a serial read operation i e a rising edge Analog Input Channel The input channel is single ended with respect to GND The input channel can convert voltage signals in the range 0 V to 2 5 V The input channel is selected by writing to the Address Register of the AD7818 see Control Byte section 4 AD7816 REFqi Reference Input An external 2 5 V reference can be connected to the AD7816 at this pin To enable the on chip reference the REFy pin should be tied to AGND If an external reference is connected to the AD7816 the internal reference will shut down 5 Vpp Positive supply voltage 2 7 V to 5 5 V 6 Dmiour Logic Input and Output Serial data is clocked in and out of the AD7816 AD7818 at this pin 7 SCLK Clock Input for the Serial Port The serial clock is used to clock data into and out of the AD7816 AD7818 Data is clocked out on the falling edge and clocked in on the rising edge 8 RD WR Logic Input The read write signal is used to indicate to the AD7816 and AD7818 whether the next data transfer operation is a read or a write The RD WR should be set logic high for a read operation and logic low for a write PIN CONFIGURATIONS Total Harmonic Distortion Total harmonic distortion THD is the ratio of the rms sum of SOIC MSOP AD7816 harmonics to the fundamental For the AD7801 it is defined as CONVST 1 e fe ROAR W2 V2 V2 V2 V2 2 OBI SCLK THD dB
21. ed by connecting the REF pin to analog ground CONVERTER DETAILS Conversion is initiated by pulsing the CONVST input The conversion clock for the part is internally generated so no exter nal clock is required except when reading from and writing to the serial port The on chip track hold goes from track to hold mode and the conversion sequence is started on the falling edge of the CONVST signal At this point the BUSY signal goes high and low again 9 us or 27 us later depending on whether an analog input or the temperature sensor is selected to indicate the end of the conversion process This signal can be used by a microcontroller to determine when the result of the conversion should be read The track hold acquisition time of the AD7817 and AD7818 is 400 ns A temperature measurement is made by selecting the Channel 0 of the on chip MUX and carrying out a conversion on this channel A conversion on Channel 0 takes 27 us to complete Temperature measurement is explained in the Temperature Measurement section of this data sheet The on chip reference is not available to the user but REFpy can be overdriven by an external reference source 2 5 V only The effect of reference tolerances on temperature measurements is discussed in the section titled Temperature Measurement Error Due to Reference Error All unused analog inputs should be tied to a voltage within the nominal analog input range to avoid noise pickup For mini mum power c
22. els Relative Accuracy Relative accuracy or endpoint nonlinearity is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC Offset Error This is the deviation of the first code transition 0000 000 to 0000 001 from the ideal i e AGND 1 LSB Offset Error Match This is the difference in Offset Error between any two channels Gain Error This is the deviation of the last code transition 1111 110 to 1111 111 from the ideal i e VREF 1 LSB after the offset error has been adjusted out Gain Error Match This is the difference in Gain Error between any two channels Track Hold Acquisition Time Track hold acquisition time is the time required for the output of the track hold amplifier to reach its final value within 1 2 LSB after the end of conversion the point at which the track hold returns to track mode It also applies to situations where a change in the selected input channel takes place or where there is a step input change on the input voltage applied to the selected input of the AD7817 or AD7818 It means that the user must wait for the duration of the track hold acqui sition time after the end of conversion or after a channel change step input change to before starting another conversion to ens
23. f this power dissipation The graphs below show the self heating effect in a 16 lead SOIC package Figures 12 and 13 show the self heating effect on a two layer and four layer PCB The plots were generated by assembling a heater resistor REV AD7816 AD7817 AD7818 and temperature sensor diode in the package being evaluated In Figure 12 the heater 6 mW is turned off after 30 sec The PCB has little influence on the self heating over the first few seconds after the heater is turned on This can be more clearly seen in Figure 13 where the heater is switched off after 2 sec onds Figure 14 shows the relative effects of self heating in air fluid and in thermal contact with a large heat sink These diagrams represent the worst case effects of self heating The heater delivered 6 mW to the interior of the package in all cases This power level is equivalent to the ADC continuously converting at 100 kSPS The effects of the self heating can be reduced at lower ADC throughput rates by operating on Mode 2 see Operating Modes section When operating in this mode the on chip power dissipation reduces dramatically and as a consequence the self heating effects 0 50 0 45 2 LAYER PCB 0 40 0 35 0 30 TEMPERATURE C o 0 15 0 10 0 05 0 00 0 05 10 20 30 40 50 60 TIME secs Figure 12 Self Heating Effect Two Layer and Four Layer PCB 2 LAYER PCB
24. gic low and high again At the end of the read opera tion the Dnyovr pin becomes a logic input on the falling edge of RD WR Write Operation A control byte write operation to the AD7816 and AD7818 is also shown in Figure 21 The RD WR input goes low to indicate to the part that a serial write is about to occur The AD7816 and AD7818 control bytes are loaded on the rising edge of the first eight clock cycles of the serial clock with data on all subse quent clock cycles being ignored To carry out a successive write to the AD7816 or AD7818 the RD WR pin must be brought logic high and low again REV C AD7816 AD7817 AD7818 RD WR SCLK Diw Dout 74 CONTROL BYTE Figure 21 AD7816 AD7818 Serial Interface Timing Diagram OUTLINE DIMENSIONS 8 Lead Standard Small Outline Package SOIC Narrow Body R 8 Dimensions shown in millimeters and inches 5 00 0 1968 MS 0 1880 8 5 4 00 0 1574 6 20 0 2440 3 80 0 1497 4 5 80 0 2284 d EE 1 27 0 0500 0 50 0 0196 15 BSC 1 75 0 0688 0 25 0 0099 0 25 0 0098 1 35 0 0532 0 10 0 0040 Y y D 0 51 0 0201 4 8 gt COPLANARITY We 16051 00201 0 25 0 0098 0 1 27 0 0500 0 10 PLANE 0 17 0 0067 0 40 0 0157 COMPLIANT TO JEDEC STANDARDS MS 012AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS INCH DIMENSIONS IN PARENTHESES ARE ROUNDED OFF MILLIMETER EQUIVALENTS FOR R
25. he entire eight bits of the control byte are transferred to the Overtemperature Register see Figure 4 At the end of a tem perature conversion a digital comparison is carried out between the 8 MSBs of the temperature conversion result 10 bits and the contents of the Overtemperature Register 8 bits If the result of the temperature conversion is greater that the contents of the Overtemperature Register OTR then the Overtemperature Indicator goes logic low The resolution of the OTR is 1 C The lowest temperature that can be written to the OTR is 95 C and the highest is 152 C see Figure 5 However the usable temperature range of the temperature sensor is 55 C to 125 C Figure 5 shows the OTR and how to set Tay arm the temperature at which the OTI goes low OTR Dec Tyrarm C 103 C For example to set to 50 OTR 50 103 153 Dec or 10011001 Bin If the result of a temperature conversion exceeds 50 C then OTI will go logic low The OTI logic output is reset high at the end of a serial read operation or if a new temperature measurement is lower than Tar apm The default power on Tay is 50 082 1 060 ADDRESS REGISTER IF DB7 TO DB3 ARE LOGIC 0 THEN DB2 TO DBO ARE WRITTEN TO THE ADDRESS REGISTER MSB LSB paz pes pes 062 061 peo conTROL BYTE IF ANY BIT DB7 TO DB3 IS SET TO A LOGIC 1 THEN THE FULL 8 BITS OF THE CONTROL WORD
26. his point i e when BUSY goes low the devices will power down The devices are powered up again on the rising edge of the CONVST signal Superior power performance can be achieved in this mode of operation by powering up the AD7816 AD7817 and AD7818 only to carry out a conversion see Power vs Throughput section In Figure 17 the CS line is applicable to the AD7817 only I bur DB7 DB9 DBO Figure 16 Mode 7 Operation 14 REV AD7816 AD7817 AD7818 trower uP CONVST CS a Dur DB7 DB9 DBO Figure 17 Mode 2 Operation POWER VS THROUGHPUT Superior power performance can be achieved by using the Auto matic Power Down Mode 2 at the end of a conversion see Operating Modes section of this data sheet tpower up tcoNvERT 4 25s 8 5 gt CONVST BUSY 1005 10kSPS E E Figure 18 Automatic Power Down Figure 18 shows how the Automatic Power Down is imple mented to achieve the optimum power performance from the AD7816 AD7817 and AD7818 The devices are operated in Mode 2 and the duration of CONVST pulse is set to be equal to the power up time 2 us As the throughput rate of the device is reduced the device remains in its power down state longer and the average power consumption over time drops accordingly For example if the AD7817 is operated in a continuous sam pling mode with a through
27. ime after SCLK Falling Edge Hae 30 ns max Dour Bus Relinquish Time after Falling Edge of RD WR tap 30 ns max Dour Bus Relinquish Time after Rising Edge of CS 015 150 BUSY Falling Edge to OTI Falling Edge tie 40 ns min RD WR Rising Edge to OTI Rising Edge ti7 400 ns min SCLK Rising Edge to CONVST Falling Edge Acquisition Time of T H NOTES Sample tested during initial release and after any redesign or process change that may affect this parameter All input signals are measured with tr tf 1 ns 10 to 90 of 5 V and timed from a voltage level of 1 6 V See Figures 16 17 20 and 21 These figures are measured with the load circuit of Figure 3 They are defined as the time required for D to cross 0 8 V or 2 4 V for Vpp 5 V 1096 and 0 4 V or 2 V for Vpp 3 V 10 as quoted on the specifications page of this data sheet These times are derived from the measured time taken by the data outputs to change 0 5 V when loaded with the circuit of Figure 3 The measured number is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor This means that the times quoted in the timing characteristics are the true bus relinquish times of the part and as such are independent of external bus loading capacitances Specifications subject to change without notice TO OUTPUT PIN 1 6V Figure 3 Load Circuit for Access Time and Bus Relinquish Time REV C 5 AD7816 AD7817 AD7818
28. ment Error External Reference Vggg 2 5 V Ambient Temperature 25 C 2 C max Tmn to Tmax 3 C max Measurement Error On Chip Reference Ambient Temperature 25 C 2 C max Tmn to Tmax 3 C max Temperature Resolution 1 4 C LSB REFERENCE INPUT AD7816 Only REFy Input Voltage Range 2 625 V max 2 5 V 596 2 375 V min 2 5 V 5 Input Impedance 50 kQ min Input Capacitance 10 pF max ON CHIP REFERENCE Nominal 2 5 V Temperature Coefficient 30 ppm C typ CONVERSION RATE Track Hold Acquisition Time 400 ns max Source Impedance lt 10 Q Conversion Time Temperature Sensor 27 us max Channel 1 9 us max AD7818 Only POWER REQUIREMENTS Vpp 5 5 V max For Specified Performance 2 7 V min Ipp Logic Inputs 0 V or Vpp Normal Operation 2 mA max 1 3 mA typ Using External Reference 1 75 mA max 2 5 V External Reference Connected Power Down Vpp 5 V 10 75 uA max 6 uA typ Power Down Vpp 3 V 4 5 uA max 2 uA typ Auto Power Down Mode Vpp 3V 10 SPS Throughput Rate 6 4 uW typ See Power vs Throughput Section for 1 kSPS Throughput Rate 48 8 uW typ Description of Power Dissipation in 10 KSPS Throughput Rate 434 uW typ Auto Power Down Mode Power Down 13 5 uW max Typically 6 yW REV AD7816 AD7817 AD7818 SPECIFICATIONS Parameter A Version B Version S Version Unit Test Conditions Comments ANALOG INPUTS AD7817 and AD7818 Input Voltage Range VREF VREF VREF V max 0 0 0 V min Input Leakage 1 1 1 uA min Input
29. nputs 0 V or Vpp Normal Operation 2 2 2 mA max 1 6 mA typ Using External Reference 1 75 1 75 1 75 mA max 2 5 V External Reference Connected Power Down Vpp 5 V 10 10 12 5 uA max 5 5 uA typ Power Down Vpp 3 V 4 4 4 5 uA max 2 uA typ Auto Power Down Mode Vpp 3 V 10 SPS Throughput Rate 6 4 6 4 6 4 uW typ See Power vs Throughput Section for 1 kSPS Throughput Rate 48 8 48 8 48 8 uW typ Description of Power Dissipation in 10 kKSPS Throughput Rate 434 434 434 uW typ Auto Power Down Mode Power Down 12 12 13 5 uW max Typically 6 uW REV AD7816 AD7818 SPECIFICATIONS AD7816 AD7817 AD7818 Voo 2 7 V to 5 5 V GND 0 V REF 2 5 V unless otherwise noted Parameter A Version Unit Test Conditions Comments DYNAMIC PERFORMANCE AD7818 Only Sample Rate 100 kSPS Any Channel fin 20 kHz Signal to Noise Distortion Ratio 57 dB min Total Harmonic Distortion 65 dB max 75 dB typ Peak Harmonic or Spurious Noise 67 dB typ 75 dB typ Intermodulation Distortion fa 19 9 kHz fb 20 1 kHz Second Order Terms 67 dB typ Third Order Terms 67 Channel to Channel Isolation 80 dB typ fw 20 kHz DC ACCURACY AD7818 Only Any Channel Resolution 10 Bits Minimum Resolution for Which No Missing Codes are Guaranteed 10 Bits Relative Accuracy 1 LSB max Differential Nonlinearity 1 LSB max Gain Error 10 LSB max Offset Error 4 LSB max TEMPERATURE SENSOR Measure
30. onsumption the unused analog inputs should be tied to AGND REV C TYPICAL CONNECTION DIAGRAM Figure 6 shows a typical connection diagram for the AD7817 The AGND and DGND are connected together at the device for good noise suppression The BUSY line is used to interrupt the microcontroller at the end of the conversion process and the serial interface is implemented using three wires see Serial Interface section for more details An external 2 5 V reference can be connected at the REFy pin If an external reference is used a 10 uF capacitor should be connected between REF and AGND For applications where power consumption is of concern the automatic power down at the end of a conversion should be used to improve power performance See Power vs Throughput section of this data sheet SUPPLY 2 7V TO O 5 5V 3 WIRE SERIAL INTERFACE ov TO 2 5v Icy INPUT O V Q pC pP AD7817 OPTIONAL EXTERNAL AD780 __ REFERENCE LREF 192 Figure 6 Typical Connection Diagram EXTERNAL V g REFERENCE ANALOG INPUTS Analog Input Figure 7 shows an equivalent circuit of the analog input struc ture of the AD7817 and AD7818 The two diodes D1 and D2 provide ESD protection for the analog inputs Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 200 mV This will cause these diodes to become forward biased and start conducting current into the substrate
31. put rate of 10 kSPS the power con sumption is calculated as follows The power dissipation during normal operation is 4 8 mW Vpp 3 V If the power up time is 2 us and the conversion time is 9 us the AD7817 can be said to dissipate 4 8 mW typically for 11 us worst case during each conversion cycle If the throughput rate is 10 kSPS the cycle time is 100 us and the power dissipated while powered up dur ing each cycle is 11 100 x 4 8 mW 528 uW typ Power dissipated while powered down during each cycle is 89 100 x 3 Vx 2 WA 5 34 uW typ Overall power dissipated is 528 uW 5 34 uW 533 UW REV 10 POWER mW 0 01 0 10 20 30 40 50 60 70 80 THROUGHPUT kHz Figure 19 Power vs Throughput Rate AD7817 SERIAL INTERFACE The serial interface on the AD7817 is a 5 wire interface with read and write capabilities with data being read from the output register via the Doyr line and data being written to the control register via the line The part operates in a slave mode and requires an externally applied serial clock to the SCLK input to access data from the data register or write to the control byte The RD WR line is used to determine whether data is being written to or read from the AD7817 When data is being written to the AD7817 the RD WR line is set logic low and when data is being read from the part the line is set logic high see Figure 20 The serial in
32. s applied specifications are typical for AD7818 at temperatures above 85 C and with Vpp greater than 3 6 V Refers to the input current when the part is not converting Primarily due to reverse leakage current in the ESD protection diodes Specifications subject to change without notice SAMPLING CAPACITOR AGND CONVST Figure 1 AD7816 Functional Block Diagram SAMPLING CAPACITOR AGND CONVST Figure 2 AD7818 Functional Block Diagram REV TIMING CHARACTERISTICS AD7816 AD7817 AD7818 2 Voo 2 7 V to 5 5 V GND 0 V 2 5 V All specifications to Tmax unless otherwise noted Parameter A B Versions Unit Test Conditions Comments tpowER UP 2 us max Power Up Time from Rising Edge of CONVST tja 9 us max Conversion Time Channels 1 to 4 tib 27 us max Conversion Time Temperature Sensor to 20 ns min CONVST Pulse Width t5 50 ns max CONVST Falling Edge to BUSY Rising Edge t4 0 ns min CS Falling Edge to RD WR Falling Edge Setup Time t5 0 ns min RD WR Falling Edge to SCLK Falling Edge Setup te 10 ns min Dyy Setup Time before SCLK Rising Edge t 10 ns min D y Hold Time after SCLK Rising Edge tg 40 ns min SCLK Low Pulse Width to 40 ns min SCLK High Pulse Width tio 0 ns min CS Falling Edge to RD WR Rising Edge Setup Time tu 0 ns min RD WR Rising Edge to SCLK Falling Edge Setup Time ty 20 ns max Dour Access Time after RD WR Rising Edge ti 20 ns max Dour Access T
33. t is erased A conversion must be done again otherwise no data will be read back Write Operation Figure 20 also shows a control byte write operation to the AD7817 The RD WR input goes low to indicate to the part that a serial write is about to occur The AD7817 control byte is loaded on the rising edge of the first eight clock cycles of the serial clock with data on all subsequent clock cycles being ignored To carry out a second successive write operation the RD WR signal must be brought high and low again Simplifying the Serial Interface To minimize the number of interconnect lines to the AD7817 the user can connect the CS line to DGND This is possible if the AD7817 is not sharing the serial bus with another device It is also possible to tie the and Dour lines together This arrangement is compatible with the 8051 microcontroller The 68HC11 68HC05 and PIC16Cxx can be configured to operate with a single serial data line In this way the number of lines required to operate the serial interface can be reduced to three i e RD WR SCLK and 20007 see Figure 6 AD7816 AND AD7818 SERIAL INTERFACE MODE The serial interface on the AD7816 and AD7818 is a 3 wire interface with read and write capabilities Data is read from the 16 output register and the control byte is written to the AD7816 and AD7818 via the Dyy our line The part operates in a slave mode and requires an externally applied serial clock to the SCLK input
34. terface on the AD7817 is designed to allow the part to be interfaced to systems that provide a serial clock that is synchronized to the serial data such as the 80C51 87C51 68HC11 68HC05 and PIC16Cxx microcontrollers 15 AD7816 AD7817 AD7818 RD WR SCLK Din Dour Figure 20 AD7817 Serial Interface Timing Diagram Read Operation Figure 20 shows the timing diagram for a serial read from the AD7817 CS is brought low to enable the serial interface and RD WR is set logic high to indicate that the data transfer is a serial read from the AD7817 The rising edge of clocks out the first data bit DB9 subsequent bits are clocked out on the falling edge of SCLK except for the first falling SCLK edge and are valid on the rising edge 10 bits of data are transferred during a read opera tion However the user has the choice of clocking only eight bits if the full 10 bits of the conversion result are not required The serial data can be accessed in a number of bytes if 10 bits of data are being read However RD WR must remain high for the duration of the data transfer operation Before starting a new data read opera tion the RD WR signal must be brought low and high again At the end of the read operation the Dour line enters a high impedance state on the rising edge of the CS or the falling edge of RD WR whichever occurs first The readback process is a destructive process in that once the data is read back i
35. to access data from the data register or write the control byte The RD WR line is used to determine whether data is being written to or read from the AD7816 and AD7818 When data is being written to the devices the RD WR line is set logic low and when data is being read from the part the line is set logic high see Figure 21 The serial interface on the AD7816 and AD7818 are designed to allow the part to be interfaced to systems that provide a serial clock that is synchronized to the serial data such as the 80C51 87C51 68HC11 68HC05 and PIC16Cxx microcontrollers Read Operation Figure 21 shows the timing diagram for a serial read from the AD7816 and AD7818 The RD WR is set logic high to indicate that the data transfer is a serial read from the devices When RD WR is logic high the Dour pin becomes a logic output and the first data bit DB9 appears on the pin Subsequent bits are clocked out on the falling edge of SCLK starting with the second SCLK falling edge after RD WR goes high and are valid on the rising edge of SCLK Ten bits of data are transferred during a read operation However the user has the choice of clocking only eight bits if the full 10 bits of the conversion result are not required The serial data can be accessed in a number of bytes if 10 bits of data are being read however RD WR must remain high for the duration of the data transfer operation To carry out a successive read operation the RD WR pin must be brought lo
36. typ Intermodulation Distortion fa 219 9 kHz fb 20 1 kHz Second Order Terms 67 67 67 dB typ Third Order Terms 67 67 67 dB typ Channel to Channel Isolation 80 80 80 dB typ fw 20 kHz DC ACCURACY Any Channel Resolution 10 10 10 Bits Minimum Resolution for Which No Missing Codes are Guaranteed 10 10 10 Bits Relative Accuracy aspi 1 1 LSB max Differential Nonlinearity 1 1 1 LSB max Gain Error 2 2 2 LSB max External Reference 10 10 20 10 LSB max Internal Reference Gain Error Match 1 2 1 2 1 2 LSB max Offset Error 2 2 2 LSB max Offset Error Match 1 2 1 2 1 2 LSB max TEMPERATURE SENSOR Measurement Error External Reference Vpgr 2 5 V Ambient Temperature 25 C 2 1 2 C max Tmn to Tmax 3 2 3 C max Measurement Error On Chip Reference Ambient Temperature 25 C 52 25 2 25 T225 C max Tmn to 3 3 6 C max Temperature Resolution 1 4 1 4 1 4 C LSB REFERENCE INPUT 4 REFy Input Voltage Range 2 625 2 625 2 625 V max 2 5 V 5 2 375 2 375 2 375 V min 2 5 V 5 Input Impedance 40 40 40 kQ min Input Capacitance 10 10 10 pF max ON CHIP REFERENCE Nominal 2 5 V Temperature Coefficient 80 80 150 ppm C typ CONVERSION RATE Track Hold Acquisition Time 400 400 400 ns max Source Impedance lt 10 Q Conversion Time Temperature Sensor 27 27 27 us max Channels 1 to 4 9 9 9 us max POWER REQUIREMENTS Vpp 5 5 5 5 5 5 V max For Specified Performance 2 7 21 2 1 V min Ipp Logic I
37. ure that the part operates to specification CONTROL BYTE The AD7816 AD7817 and AD7818 contain two on chip regis ters the Address Register and the Overtemperature Register These registers can be accessed by carrying out an 8 bit serial write operation to the devices The 8 bit word or control byte written to the AD7816 AD7817 and AD7818 is transferred to one of the two on chip registers as follows 10 Address Register If the five MSBs of the control byte are logic zero the three LSBs of the control byte are transferred to the Address Regis ter see Figure 4 The Address Register is a 3 bit wide register used to select the analog input channel on which to carry out a conversion It is also used to select the temperature sensor which has the address 000 Table I shows the selection The Internal Reference selection connects the input of the ADC to a band gap reference When this selection is made and a conver sion is initiated the ADC output should be approximately mid scale After power up the default channel selection is DB2 DB1 DBO 0 Temperature Sensor Table I Channel Selection DB2 Channel Selection Device 0 0 0 Temperature Sensor All 0 0 1 Channel 1 AD7817 AD7818 0 1 0 Channel 2 AD7817 0 1 1 Channel 3 AD7817 1 0 0 Channel 4 AD7817 1 1 1 Internal Ref 1 23 V All Overtemperature Register If any of the five MSBs of the control byte are logic one then t
38. ves at two frequencies fa and fb any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa nfb where m n 0 1 2 3 etc Intermodulation terms are those for which neither m nor n are equal to zero For example the second order terms include fa fb and fa fb while the third order terms include 213 fb 213 fb fa 2fb and fa 216 AD7816 AD7817 AD7818 The AD7816 AD7817 and AD7818 are tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used In this case the second and third order terms are of different significance The second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies As a result the second and third order terms are specified separately The calculation of the intermodu lation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the fundamental expressed in dBs Channel to Channel Isolation Channel to channel isolation is a measure of the level of crosstalk between channels It is measured by applying a full scale 20 kHz sine wave signal to one input channel and deter mining how much that signal is attenuated in each of the other channels The figure given is the worst case across all four chann
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ANALOG DEVICES AD7816/AD7817/AD7818 handbook analog devices p/n ad8479 ad717x_connect_analog_input