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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, nor for any infringements of patents or other rights of third 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. 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 single- and 4-channel, 9 s, 10-bit adcs with on-chip temperature sensor functional block diagram features 10-bit adc with 9 s conversion time one (ad7818) and four (ad7817) single-ended analog input channels th e ad7816 is a temperature measurement only device on-chip temperature sensor resolution of 0.25 c 2 c error from ?0 c to +85 c ?5 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 w at a throughput rate of 10 sps 40 w at a throughput rate of 1 ksps 400 w 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 s 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-and- 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 r esolution of 0.25 c. see temperature measurement section of this data sheet. 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 mic rowire 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- 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. th e devices have an on-chip temperature sensor that allows an accurate m easurement of the ambient temperature to be m ade. the measurable temperature range is ?5 c to +125 c. 2. 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. 3. the automatic power-down feature enables the ad7816, ad7817, and ad7818 to achieve superior power perfor- mance at slower throughput rates, e.g., 40 w at 1 ksps throughput rate. charge redistribution dac clock d out sclk rd/ wr convst agnd control reg a b overtemp reg a > b oti control logic v balance sampling capacitor mux ref 2.5v temp sensor ref in v dd data out d in dgnd busy cs v in1 v in2 v in3 v in4 ad7817
rev. c e2e ad7816/ad7817/ad7818 parameter a version * b version * s version unit test conditions/comments dynamic performance sample rate = 100 ksps, any channel, f in = 20 khz signal to (noise + distortion) ratio 2 58 58 58 db min total harmonic distortion 2 e65 e65 e65 db max e75 db typ peak harmonic or spurious noise 2 e65 e65 e65 db max e75 db typ intermodulation distortion 2 fa =19.9 khz, fb = 20.1 khz second order terms e67 e67 e67 db typ third order terms e67 e67 e67 db typ channel-to-channel isolation 2 e80 e80 e80 db typ f in = 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 2 1 1 1lsb max differential nonlinearity 2 1 1 1lsb max gain error 2 2 2 2l sb max external reference 10 10 +20/e10 lsb max internal reference gain error match 2 1/2 1/2 1/2 lsb max offset error 2 2 2 2lsb max offset error match 1/2 1/2 1/2 lsb max temperature sensor 1 measurement error external reference v ref = 2.5 v ambient temperature 25 c 2 1 2 c max t min to t max 3 2 3 c max measurement error on-chip reference ambient temperature 25 c 2.25 2.25 2.25 c max t min to t max 3 3 6 c max temperature resolution 1/4 1/4 1/4 c/lsb reference input 3, 4 ref in input voltage range 3 2.625 2.625 2.625 v max 2.5 v + 5% 2.375 2.375 2.375 v min 2.5 v e 5% input impedance 40 40 40 k min input capacitance 10 10 10 pf max on-chip reference 5 nominal 2.5 v temperature coefficient 3 80 80 150 ppm/ c typ conversion rate track/hold acquisition time 4 400 400 400 ns max source impedance < 10 conversion time temperature sensor 27 27 27 s max channels 1 to 4 9 9 9 s max power requirements v dd 5.5 5.5 5.5 v max for specified performance 2.7 2.7 2.7 v min i dd logic inputs = 0 v or v dd 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 (v dd = 5 v) 10 10 12.5 a max 5.5 a typ power-down (v dd = 3 v) 4 4 4.5 a max 2 a typ auto power-down mode v dd = 3 v 10 sps throughput rate 6.4 6.4 6.4 w typ see power vs. throughput section for 1 ksps throughput rate 48.8 48.8 48.8 w typ description of power d issipation in 10 ksps throughput rate 434 434 434 w typ auto power-down mode power-down 12 12 13.5 w max typically 6 w ad7817especifications 1 (v dd = 2.7 v to 5.5 v, gnd = 0 v, ref in = 2.5 v unless otherwise noted)
rev. c ad7816/ad7817/ad7818 e3e parameter a version unit test conditions/comments dynamic performance (ad7818 only) sample rate = 100 ksps, any channel, f in = 20 khz signal to (noise + distortion) ratio 2 57 db min total harmonic distortion 2 e65 db max e75 db typ peak harmonic or spurious noise 2 e67 db typ e75 db typ intermodulation distortion 2 fa = 19.9 khz, fb = 20.1 khz second order terms e67 db typ third order terms e67 db typ channel-to-channel isolation 2 e80 db typ f in = 20 khz dc accuracy (ad7818 only) any channel resolution 10 bits minimum resolution for which no missing codes are guaranteed 10 bits relative accuracy 2 1 lsb max differential nonlinearity 2 1 lsb max gain error 2 10 lsb max offset error 2 4 lsb max temperature sensor 1 measurement error external reference v ref = 2.5 v ambient temperature 25 c 2 c max t min to t max 3 c max measurement error on-chip reference ambient temperature 25 c 2 c max t min to t max 3 c max temperature resolution 1/4 c/lsb reference input 3, 4 (ad7816 only) ref in input voltage range 3 2.625 v max 2.5 v + 5% 2.375 v min 2.5 v e 5% input impedance 50 k min input capacitance 10 pf max on-chip reference 5 nominal 2.5 v temperature coefficient 3 30 ppm/ c typ conversion rate track/hold acquisition time 4 400 ns max source impedance < 10 conversion time temperature sensor 27 s max channel 1 9 s max (ad7818 only) power requirements v dd 5.5 v max for specified performance 2.7 v min i dd logic inputs = 0 v or v dd normal operation 2 ma max 1.3 ma typ using external reference 1.75 ma max 2.5 v external reference connected power-down (v dd = 5 v) 10.75 a max 6 a typ power-down (v dd = 3 v) 4.5 a max 2 a typ auto power-down mode v dd = 3 v 10 sps throughput rate 6.4 w typ see power vs. throughput section for 1 ksps throughput rate 48.8 w typ description of power dissipation in 10 ksps throughput rate 434 w typ auto power-down mode power-down 13.5 w max typically 6 w ad7816/ad7818 6 especifications 1 (v dd = 2.7 v to 5.5 v, gnd = 0 v, ref in = 2.5 v unless otherwise noted)
rev. c e4e ad7816/ad7817/ad7818especifications parameter a version * b version * s version unit test conditions/comments analog inputs 7 (ad7817 and ad7818) input voltage range v ref v ref v ref v max 0 00v min input leakage 1 1 1 a min input capacitance 10 10 10 pf max logic inputs 4 input high voltage, v inh 2.4 2.4 2.4 v min v dd = 5 v 10% input low voltage, v inl 0.8 0.8 0.8 v max v dd = 5 v 10% input high voltage, v inh 2 22v minv dd = 3 v 10% input low voltage, v inl 0.4 0.4 0.4 v max v dd = 3 v 10% input current, i in 3 3 3 a max typically 10 na, v in = 0 v to v dd input capacitance, c in 10 10 10 pf max logic outputs 4 output high voltage, v oh i source = 200 a 4 44v minv dd = 5 v 10% 2.4 2.4 2.4 v min v dd = 3 v 10% output low voltage, v ol i sink = 200 a 0.4 0.4 0.4 v max v dd = 5 v 10% 0.2 0.2 0.2 v max v dd = 3 v 10% high impedance leakage current 1 1 1 a 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. 1 ad7816 and ad7817 temperature sensors specified with external 2.5 v reference, ad7818 specified with on-chip reference. all oth er specifications with external and on-chip reference (2.5 v). for v dd = 2.7 v, t a = 85 c max and temperature sensor measurement error = 3 c. 2 see terminology. 3 the 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. 4 sample tested during initial release and after any redesign or process change that may affect this parameter. 5 on-chip reference shuts down when external reference is applied. 6 all specifications are typical for ad7818 at temperatures above 85 c and with v dd greater than 3.6 v. 7 refers to the input current when the part is not converting. primarily due to reverse leakage current in the esd protection dio des. specifications subject to change without notice. charge redistribution dac clock data out d in/ out sclk rd/ wr convst agnd control reg a b overtemp reg a > b oti control logic v balance sampling capacitor mux ref 2.5v temp sensor ref in v dd ad7816 figure 1. ad7816 functional block diagram charge redistribution dac clock generator data out d in/ out sclk rd/ wr convst agnd control reg a b overtemp reg a > b oti control logic v balance sampling capacitor mux ref 2.5v temp sensor v dd v in1 ad7818 figure 2. ad7818 functional block diagram
rev. c ad7816/ad7817/ad7818 e5e timing characteristics 1, 2 parameter a, b versions unit test conditions/comments t power-up 2 s max power-up time from rising edge of convst ctc ctts convst w convst busyr cs r wr st r wr scs in stscr in tscr scw scw cs r wr rst r wr rscst out tr wr r out tsc out brtr wr out brtr cs busy oti r wr r oti r scr convst tt nots s v v s tt out vvv v v vv v t v t t s v i o i o to outut in c ctbrt v vvn vr in vt in t
rev. c e6e ad7816/ad7817/ad7818 absolute maximum ratings 1 ( t a = 25 c unless otherwise noted) v dd to agnd . . . . . . . . . . . . . . . . . . . . . . . . . e0.3 v to +7 v v dd to dgnd . . . . . . . . . . . . . . . . . . . . . . . . . e0.3 v to +7 v analog input voltage to agnd v in1 to v in4 . . . . . . . . . . . . . . . . . . . e0.3 v to v dd + 0.3 v reference input voltage to agnd 2 . . . e0.3 v to v dd + 0.3 v digital input voltage to dgnd . . . . . . e0.3 v to v dd + 0.3 v digital output voltage to dgnd . . . . . e0.3 v to v dd + 0.3 v storage temperature range . . . . . . . . . . . . . e65 c to +150 c junction temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150 c tssop, power dissipation . . . . . . . . . . . . . . . . . . . . 450 mw ja 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 ja thermal impedance . . . . . . . . . . . . . . . . . . . . . 100 c/w lead temperature, soldering vapor phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215 c infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220 c 8-lead soic package, power dissipation . . . . . . . . . . 450 mw ja thermal impedance . . . . . . . . . . . . . . . . . . . . . 157 c/w lead temperature, soldering vapor phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215 c infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220 c soic package, power dissipation . . . . . . . . . . . . . . 450 mw ja thermal impedance . . . . . . . . . . . . . . . . . . . . . 206 c/w lead temperature, soldering vapor phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215 c infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220 c notes 1 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. 2 if the reference input voltage is likely to exceed v dd 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 in pin and v dd pin. the diagram below shows how the diode should be connected. ref in v dd bat81 ad7816/ad7817
rev. c ad7816/ad7817/ad7818 e7e 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. warning! esd sensitive device ordering guide temperature temperature package package model range error @ +25 c description options branding ad7816ar e40 c to +85 c 2 c 8-lead narrow body (soic) r-8 ad7816ar-reel e40 c to +85 c 2 c 8-lead narrow body (soic) r-8 AD7816AR-REEL7 e40 c to +85 c 2 c 8-lead narrow body (soic) r-8 ad7816arm e40 c to +85 c 2 c 8-lead msop rm-8 c4a ad7816arm-reel e40 c to +85 c 2 c 8-lead msop rm-8 c4a ad7816arm-reel7 e40 c to +85 c 2 c 8-lead msop rm-8 c4a ad7816achips die ad7817ar e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7817ar-reel e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7817ar-reel7 e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7817arz * e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7817aru e40 c to +85 c 2 c 16-lead (tssop) ru-16 ad7817aru-reel e40 c to +85 c 2 c 16-lead (tssop) ru-16 ad7817aru-reel7 e40 c to +85 c 2 c 16-lead (tssop) ru-16 ad7817br e40 c to +85 c 1 c 16-lead narrow body (soic) r-16 ad7817br-reel e40 c to +85 c 1 c 16-lead narrow body (soic) r-16 ad7817br-reel7 e40 c to +85 c 1 c 16-lead narrow body (soic) r-16 ad7817brz * e40 c to +85 c 1 c 16-lead narrow body (soic) r-16 ad7817brz-reel * e40 c to +85 c 1 c 16-lead narrow body (soic) r-16 ad7817brz-reel7 * e40 c to +85 c 1 c 16-lead narrow body (soic) r-16 ad7817bru e40 c to +85 c 1 c 16-lead (tssop) ru-16 ad7817bru-reel e40 c to +85 c 1 c 16-lead (tssop) ru-16 ad7817bru-reel7 e40 c to +85 c 1 c 16-lead (tssop) ru-16 ad7817sr e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7817sr-reel e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7817sr-reel7 e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7818ar e40 c to +85 c 2 c 16-lead narrow body (soic) r-16 ad7818ar-reel e40 c to +85 c 2 c 8-lead narrow body (soic) r-8 ad7818ar-reel7 e40 c to +85 c 2 c 8-lead narrow body (soic) r-8 ad7818arm e40 c to +85 c 2 c 8-lead msop rm-8 c3a ad7818arm-reel e40 c to +85 c 2 c 8-lead msop rm-8 c3a ad7818arm-reel7 e40 c to +85 c 2 c 8-lead msop rm-8 c3a eval-ad7816/ evaluation board ad7817/ad7818eb * z = pb free part
rev. c e8e ad7816/ad7817/ad7818 ad7817 pin function descriptions pin mnemonic description 1 convst ist tt t convst io busy ott oti otoi oti ctsoro tr tr wr cs cs istt n c r in ivt r in ni v in v in ictt nt vv r rc b v svvv n out owis tr wr cs in i sc cist r wr ist tr wr inconiurtion soictsso toviw ns convst out in sc r wr busy oti cs v in v n n r in v in v in v in
rev. c ad7816/ad7817/ad7818 e9e pin configurations soic/msop (ad7816) 1 2 3 4 8 7 6 5 top view (not to scale) ad7816 convst d in/out sclk rd/ wr v dd gnd ref in oti soic/msop (ad7818) 1 2 3 4 8 7 6 5 top view (not to scale) ad7818 convst d in/out sclk rd/ wr v dd gnd v in oti terminology 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 (f s /2), excluding dc. 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. total harmonic distortion total harmonic distortion (thd) is the ratio of the rms sum of harmonics to the fundamental. for the ad7891 it is defined as: thd ( db ) = 20 log v 2 2 + v 3 2 + v 4 2 + v 5 2 + v 6 2 v 1 where v 1 is the rms amplitude of the fundamental and v 2 , v 3 , v 4 , v 5 , and v 6 are the rms amplitudes of the second through the sixth harmonics. peak harmonic or spurious noise peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the adc output spectrum (up to f s /2 and excluding dc) to the rms value of the fundamental. normally, the value of this specification is deter- 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. intermodulation distortion with inputs consisting of sine waves 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 (2fa + fb), (2fa ?fb), (fa + 2fb) and (fa ?2fb). ad7816 and ad7818 pin function descriptions pin mnemonic description 1 convst ist t tt convst i o oti otoi oti ctsor otrtr wr n v in ictnt vvt rcb r in rivt r in ni v vv inout ios sc cist r wr it tr wr
rev. c e10e 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 s econd 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 channels. 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 1l sb 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 e 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 v in 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 v in before starting another conversion, to ensure that the part operates to specification. control byte t he a d7816, 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. 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 = db0 = 0 (tem perature sensor). table i. channel selection db2 db1 db0 channel selection device 00 0t emperature sensor all 00 1c hannel 1 ad7817/ad7818 01 0c hannel 2 ad7817 01 1c hannel 3 ad7817 10 0c hannel 4 ad7817 11 1i nternal ref (1.23 v) all overtemperature register if any of the five msbs of the control byte are logic one, then the 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 ( oti totr ctotr c c c cotrt r oti otr ( dec ) = t alarm ( c ) + 103 c f or example, to set t alarm to 50 c, otr = 50 + 103 = 153 dec or 10011001 bin. if the result of a temperature conversion exceeds 50 c then oti t oti t r t t r c b b b b b b b b sb sb controbyt b b b rssristr ovrtrtur ristrotr inybitbtobisstto oictntubits otcontroworrwrittn totovrtrturristr ibtobroic tnbtobrwrittn totrssristr b b b b b b b b ors
rev. c ad7816/ad7817/ad7818 e11e msb lsb 0000 000 1 minimum temperature = e95 c 11111111 maximum temperature = +152 c overtemperature register (dec) = t alarm + 103 c t alarm resolution = 1 / lsb overtemperature register db0 db1 db2 db3 db4 db5 db6 db7 figure 5. the overtemperature register (otr) circuit information the ad7817 and ad7818 are single- and four-channel, 9 s 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 in tended for temperature measurement only. the a/d converter section consists of a conventional successive-approximation co nverter 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 +v ref . 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 e55 c to +125 c. the part requires a 2.5 v reference, which can be provided from the part?s own i nternal reference or from an external reference source. the o n-chip reference is selected by connecting the ref in pin to analog ground. converter details conversion is initiated by pulsing the convst t t convst busy t t c u c tt tr in v t t r n tyicconnctionir tnn tbusy s iv r in i r in n s t v in convst n n r in suy vto v trn r rnc otion trn rrnc r vtov inut out r wr in in in in busy oti c sc wir sri intrc cs tc noinuts i t sc vt t t c tr t tc c
rev. c e12e ad7816/ad7817/ad7818 1.2v ref in sw1 2.5v external reference detect buffer 1.2v 26k 24k figure 9. on-chip reference adc transfer 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. analog input 0v 1lsb +2.5v1lsb 1lsb=2.5/1024 2.44mv adc code 111...111 111...110 111...000 011...111 000...010 000...001 000...000 figure 10. adc transfer function 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. t amb = ?03 c + ( adc code /4) ?5? 125? 192dec 912dec temperature adc code figure 11. temperature sensor transfer characteristic a in d1 c1 3pf v dd d2 c2 4pf v balance convert phase - switch open track phase - switch closed r1 1k 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 tt v in t cr rc v in c r r sc sbt t cr t charge = 7.6 ( r 2 + 1 k ) 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 the charge time for the sampling capacitor is approxi- mately 23 ns. the charge time becomes significant for source impedances of 1 k 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 ref in pin to analog ground. this causes sw1 (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 ex ternal 2.5 v reference can be connected to the ref in pin. this has the effect of shutting down the on-chip reference circuitry and reduc- ing i dd by about 0.25 ma.
rev. c ad7816/ad7817/ad7818 e13e for example, if the result of a conversion on channel 0 was 1000000000 (512 dec), the ambient temperature is equal to e 103 c + (512/4) = +25 c. t able ii below shows some adc codes for various temperatures. table ii. temperature sensor output adc code temperature 00 1100 0000 e55 c 01 0011 1000 e25 c 01 1001 1100 0 c 10 0000 0000 +25 c 10 0111 1000 +55 c 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 t emperature reading, the temperature sensor transfer function can be rewritten as a func tion of the reference voltage and the temperature. c ode ( dec ) = ([113.3285 k t ] / [ q v ref ] ? 0.6646) 1024 where: k = boltzmann? constant, 1.38 10 ?3 q = charge on an electron, 1.6 10 ?9 t =t emperature (k) so, for example, to calculate the adc code at 25 c code = ([113.3285 298 1.38 10 ?3 ]/[1.6 10 ?9 ? 2.5] ?0.6646) 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 ?%, the measurement error at ?5 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 f unction capable of a throughput rate of 100 ksps. at this t hroughput 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 of 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) 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. time ?secs temperature ? c 0.50 ?.05 060 10 20 30 40 50 0.45 0.30 0.15 0.10 0.05 0.40 0.35 0.25 0.20 0.00 4-layer pcb 2-layer pcb figure 12. self-heating effect two-layer and four-layer pcb time ?secs temperature ? c 0.25 ?.05 05 1234 0.15 0.05 0.20 0.10 0.00 4-layer pcb 2-layer pcb figure 13. self-heating effect two-layer and four-layer pcb
rev. c e14e ad7816/ad7817/ad7818 db7 e db0 db7(db9) e db0 d out convst sclk busy cs rd/ wr d in oti t 2 t 1 t 17 t 15 t 16 t 3 figure 16. mode 1 operation time e secs temperature e c 0.8 e0.01 016 46 10 12 0.5 0.2 0.7 0.4 0.0 air 0.6 0.3 0.1 28 14 fluid heat sink figure 14. self-heating effect in air, fluid, and in thermal contact with a heat sink time e secs temperature e c 0.25 e0.05 0.0 2.0 0.5 1.5 0.15 0.05 0.10 0.00 air 1.0 fluid heatsink 0.20 figure 15. self-heating effect in air, fluid, and in thermal contact with a heat sink operating modes the ad7816, ad7817, and ad7818 have two possible modes of operation depending on the state of the convst i convst busy w t w t convst busy t convst s ti cs
rev. c ad7816/ad7817/ad7818 ?5 throughput ?khz 10 1 0.01 080 10 power ?mw 0.1 20 30 40 50 60 70 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 d out line and data being written to the control register via the d in 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 interface 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. db7 ?db0 db7(db9) ?db0 d out convst sclk busy cs rd/ wr d in oti t 15 t 16 t 3 t power-up t 1 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). t power-up t convert convst busy 2 s 8 s t cycle 100 s @ 10ksps 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 s). 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 throughput rate of 10 ksps, the power con- sumption is calculated as follows. the power dissipation during normal operation is 4.8 mw, v dd = 3 v. if the power up time is 2 s and the conversion time is 9 s, the ad7817 can be said to dissipate 4.8 mw typically for 11 s (worst case) during each conversion cycle. if the throughput rate is 10 ksps, the cycle time is 100 s and the power dissipated while powered up dur- ing each cycle is (11/100) (4.8 mw) = 528 w typ. power dissipated while powered down during each cycle is (89/100) (3 v 2 a) = 5.34 w typ. overall power dissipated is 528 w + 5.34 w = 533 w.
rev. c e16e ad7816/ad7817/ad7818 read operation figure 20 shows the timing diagram for a serial read from the ad7817. cs r wr tr wr b scsc t r wr b r wr out cs r wr t wo tr wr t t r wr ssi t cs nt i in out t t ccicc i r wr sc inout nsriintrco t b b b b b b b b b b sc in r wr cs controbyt out sit inout t sc tr wr w r wr t cccc icc ro tr wr w r wr inout bs sc scr wr sct t r wr t r wr inout r wr wo tr wr t t r wr
rev. c ad7816/ad7817/ad7818 e17e sclk 13 2 123 910 rd/ wr t 7 t 14a t 13 t 12 t 11 t 8 t 9 t 5 t 6 8 7 control byte db9 db8 db7 db0 db1 db0 db1 db7 db6 db5 d in /d out figure 21. ad7816/ad7 818 serial interface timing diagram outline dimensions 16-lead standard small outline package [soic] narrow body (r-16) dimensions shown in millimeters and (inches) 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 compliant to jedec standards ms-012ac 16 9 8 1 4.00 (0.1575) 3.80 (0.1496) 10.00 (0.3937) 9.80 (0.3858) 1.27 (0.0500) bsc 6.20 (0.2441) 5.80 (0.2283) seating plane 0.25 (0.0098) 0.10 (0.0039) 0.51 (0.0201) 0.31 (0.0122) 1.75 (0.0689) 1.35 (0.0531) 8 0 0.50 (0.0197) 0.25 (0.0098) 1.27 (0.0500) 0.40 (0.0157) coplanarity 0.10 45 0.25 (0.0098) 0.17 (0.0067) 8-lead mini small outline package [msop] (rm-8) dimensions shown in millimeters 0.80 0.60 0.40 8 0 85 4 1 4.90 bsc pin 1 0.65 bsc 3.00 bsc seating plane 0.15 0.00 0.38 0.22 1.10 max 3.00 bsc coplanarity 0.10 0.23 0.08 compliant to jedec standards mo-187aa 8-lead standard small outline package [soic] narrow body (r-8) dimensions shown in millimeters and (inches) 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 85 4 1 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 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 compliant to jedec standards ms-012aa 16-lead thin shrink small outline package [tssop] (ru-16) dimensions shown in millimeters 16 9 8 1 pin 1 seating plane 8 0 4.50 4.40 4.30 6.40 bsc 5.10 5.00 4.90 0.65 bsc 0.15 0.05 1.20 max 0.20 0.09 0.75 0.60 0.45 0.30 0.19 coplanarity 0.10 compliant to jedec standards mo-153ab
rev. c e18e ad7816/ad7817/ad7818 revision history location page 9/04?data sheet changed from rev. b to rev. c. updated ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 changes to operating modes section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 changes to figure 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 changes to figure 17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 changes to ad7817 serial interface, read operation section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 changes to figure 20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 changes to figure 21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
e19e
c01316e0e9/04(c) e20e

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