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1 msps,12-bit adcs ad7475/ad7495 rev. b 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. specifications subject to chan ge without notice. no license is granted by implication or otherwise under any patent or patent ri ghts 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: 781.461.3113 ? 2005 analog devices, inc. all rights reserved. features and applications fast throughput rate: 1 msps specified for v dd of 2.7 v to 5.25 v low power: 4.5 mw max at 1 msps with 3 v supplies 10.5 mw max at 1 msps with 5 v supplies wide input bandwidth: 68 db snr at 300 khz input frequency flexible power/serial clock speed management no pipeline delays high speed serial interface: spi?-/qspi?-/microwire?-/dsp-compatible on-board reference: 2.5 v (ad7495 only) standby mode: 1 a max 8-lead msop and soic packages battery-powered systems personal digital assistants medical instruments mobile communications instrumentation and control systems data acquisition systems optical sensors general description the ad7475/ad7495 1 are 12-bit, high speed, low power, successive-approximation adcs that operate from a single 2.7 v to 5.25 v power supply with throughput rates up to 1 msps. they contain a low noise, wide bandwidth track-and- hold amplifier that can handle input frequencies above 1 mhz. the conversion process and data acquisition are controlled using cs and the serial clock, allowing the devices to interface with microprocessors or dsps. the input signal is sampled on the falling edge of cs and conversion is initiated at this point. the conversion time is determined by the sclk frequency. there are no pipeline delays associated with the part. the ad7475/ad7495 use advanced design techniques to achieve very low power dissipation at high throughput rates. with 3 v supplies and a 1 msps throughput rate, the ad7475 consumes just 1.5 ma, while the ad7495 consumes 2 ma. with 5 v supplies and 1 msps, the current consumption is 2.1 ma for the ad7475 and 2.6 ma for the ad7495. the analog input range for the parts is 0 v to ref in. the 2.5 v reference for the ad7475 is applied externally to the ref in pin, while the ad7495 has an on-board 2.5 v reference. 1 protected by u.s. patent no. 6,681,332 functional block diagrams t/h 12-bit successive approximation adc ad7475 v in gnd v dd sclk cs control logic sdata v drive ref in t/h 12-bit successive approximation adc ad7495 v in gnd v dd sclk control logic sdata v drive buf 2.5v reference ref out cs 01684-b-001 figure 1. product highlights 1. the ad7475 offers 1 msps throughput rates with 4.5 mw power consumption. 2. single-supply operation with v drive function. the ad7475/ad7495 operate from a single 2.7 v to 5.25 v supply. the v drive function allows the serial interface to connect directly to either 3 v or 5 v processor systems independent of v dd . 3. flexible power/serial clock speed management. the con- version rate is determined by the serial clock, allowing the conversion time to be reduced through the serial clock speed increase. the parts also feature shutdown modes to maximize power efficiency at lower throughput rates. this allows the average power consumption to be reduced while not converting. power consumption is 1 a when in full shutdown. 4. no pipeline delay. the parts feature a standard successive approximation adc with accurate control of the sampling instant via a cs input and once-off conversion control.
ad7475/ad7495 rev. b | page 2 of 24 table of contents ad7475 specifications ..................................................................... 3 ad7495 specifications ..................................................................... 5 timing specifications ....................................................................... 7 timing example 1 ........................................................................ 8 timing example 2 ........................................................................ 8 absolute maximum ratings ............................................................ 9 esd caution .................................................................................. 9 pin configuration and function descriptions ........................... 10 ter mi nolo g y .................................................................................... 11 typical performance curves ......................................................... 12 theory of operation ...................................................................... 13 converter operation .................................................................. 13 adc transfer function ............................................................. 13 typical connection diagram ................................................... 14 operating modes ............................................................................ 16 normal mode .............................................................................. 16 partial power-down mode ....................................................... 16 full power-down mode ............................................................ 17 power vs. throughput rate ....................................................... 19 serial interface ................................................................................ 20 microprocessor interfacing ........................................................... 21 ad7475/ad7495 to tms320c5 x /c54 x ................................. 21 ad7475/ad7495 to adsp-21 xx ............................................. 21 ad7475/ad7495 to dsp56 xxx ............................................... 22 ad7475/ad7495 to mc68hc16 ............................................. 22 outline dimensions ....................................................................... 23 ordering guide .......................................................................... 24 5/05rev. a to rev. b updated format..................................................................universal added patent information .............................................................. 1 updated outline dimensions ....................................................... 23 changes to ordering guide .......................................................... 24
ad7475/ad7495 rev. b | page 3 of 24 ad7475 specifications v dd = 2.7 v to 5.25 v, v drive = 2.7 v to 5.25 v, ref in = 2.5 v, f sclk = 20 mhz, t a = t min to t max , unless otherwise noted. table 1. parameter a version 1 b version 1 unit test conditions/comments dynamic performance signal-to-noise and distortion ratio (sinad) 68 68 db min f in = 300 khz sine wave, f sample = 1 msps total harmonic distortion (thd) ?75 ?75 db max f in = 300 khz sine wave, f sample = 1 msps peak harmonic or spurious noise (sfdr) ?76 ?76 db max f in = 300 khz sine wave, f sample = 1 msps intermodulation distortion (imd) second-order terms ?78 ?78 db typ third-order terms ?78 ?78 db typ aperture delay 10 10 ns typ aperture jitter 50 50 ps typ full power bandwidth 8.3 8.3 mhz typ @ 3 db full power bandwidth 1.3 1.3 mhz typ @ 0.1 db dc accuracy resolution 12 12 bits integral nonlinearity 1.5 1 lsb max @ 5 v (typ @ 3 v) 0.5 0.5 lsb typ @ 25c differential nonlinearity +1.5/?0.9 +1.5/?0.9 lsb max @ 5 v guaranteed no missed codes to 12 bits (typ @ 3 v) 0.5 0.5 lsb typ @ 25c offset error 8 8 lsb max typically 2.5 lsb gain error 3 3 lsb max analog input input voltage ranges 0 to ref in v dc leakage current 1 1 a max input capacitance 20 20 pf typ reference input ref in input voltage range 2.5 2.5 v 1% for specified performance dc leakage current 1 1 a max input capacitance 20 20 pf typ logic inputs input high voltage, v inh v drive ? 1 v drive ? 1 v min input low voltage, v inl 0.4 0.4 v max input current, i in 1 1 a max typically 10 na, v in = 0 v or v drive input capacitance, c in 2 10 10 pf max logic outputs output high voltage, v oh v drive ? 0.2 v min i source = 200 a; v drive = 2.7 v to 5.25 v output low voltage, v ol 0.4 0.4 v max i sink = 200 a floating-state leakage current 10 10 a max floating-state output capacitance 10 10 pf max output coding straight (natural) binary conversion rate conversion time 800 800 ns max 16 sclk cycles with sclk at 20 mhz track-and-hold acquisition time 300 300 ns max sine wave input 325 325 ns max full-scale step input throughput rate 1 1 msps max see the serial interface section
ad7475/ad7495 rev. b | page 4 of 24 parameter a version 1 b version 1 unit test conditions/comments power requirements v dd 2.7/5.25 2.7/5.25 v min/max v drive 2.7/5.25 2.7/5.25 v min/max i dd 3 digital inputs = 0 v or v drive normal mode (static) 750 750 a typ v dd = 2.7 v to 5.25 v, sclk on or off normal mode (operational) 2.1 2.1 ma max v dd = 4.75 v to 5.25 v, f sample = 1 msps 1.5 1.5 ma max v dd = 2.7 v to 3.6 v, f sample = 1 msps partial power-down mode 450 450 a typ f sample = 100 ksps partial power-down mode 100 100 a max static full power-down mode 1 1 a max sclk on or off power dissipation normal mode (operational) 10.5 10.5 mw max v dd = 5 v, f sample = 1 msps 4.5 4.5 mw max v dd = 3 v, f sample = 1 msps partial power-down (static) 500 500 w max v dd = 5 v 300 300 w max v dd = 3 v full power-down 5 5 w max v dd = 5 v 3 3 w max v dd = 3 v 1 temperature ranges for a, b versions: ?40 c to +85c. 2 guaranteed by initial characterization. 3 see the power vs. throughput rate section.
ad7475/ad7495 rev. b | page 5 of 24 ad7495 specifications v dd = 2.7 v to 5.25 v, v drive = 2.7 v to 5.25 v, f sclk = 20 mhz, t a = t min to t max, unless otherwise noted. table 2. parameter a version 1 b version 1 unit test conditions/comments dynamic performance signal-to-noise and distortion (sinad) 68 68 db min f in = 300 khz sine wave, f sample = 1 msps total harmonic distortion (thd) ?75 ?75 db max f in = 300 khz sine wave, f sample = 1 msps peak harmonic or spurious noise (sfdr) ?76 ?76 db max f in = 300 khz sine wave, f sample = 1 msps intermodulation distortion (imd) second-order terms ?78 ?78 db typ third-order terms ?78 ?78 db typ aperture delay 10 10 ns typ aperture jitter 50 50 ps typ full power bandwidth 8.3 8.3 mhz typ @ 3 db full power bandwidth 1.3 1.3 mhz typ @ 0.1 db dc accuracy resolution 12 12 bits integral nonlinearity 1.5 1 lsb max @ 5 v (typ @ 3 v) 0.5 0.5 lsb typ @ 25c differential nonlinearity +1.5/?0.9 +1.5/?0.9 lsb max @ 5 v guaranteed no missed codes to 12 bits (typ @ 3 v) 0.6 0.6 lsb typ @ 25c offset error 8 8 lsb max typically 2.5 lsb gain error 7 7 lsb max typically 2.5 lsb analog input input voltage ranges 0 to 2.5 0 to 2.5 v dc leakage current 1 1 a max input capacitance 20 20 pf typ reference output ref out output voltage 2.4625/2.5375 2.4625/2.5375 v min/max ref out impedance 10 10 typ ref out temperature coefficient 50 50 ppm/c typ logic inputs input high voltage, v inh v drive ? 1 v drive ? 1 v min input low voltage, v inl 0.4 0.4 v max input current, i in 1 1 a max typically 10 na, v in = 0 v or v drive input capacitance, c in 2 10 10 pf max logic outputs output high voltage, v oh v drive ? 0.2 v min i source = 200 a; v dd = 2.7 v to 5.25 v output low voltage, v ol 0.4 0.4 v max i sink = 200 a floating-state leakage current 10 10 a max floating-state output capacitance 10 10 pf max output coding straight (natural) binary conversion rate conversion time 800 800 ns max 16 sclk cycles with sclk at 20 mhz track-and-hold acquisition time 300 300 ns max sine wave input 325 325 ns max full-scale step input throughput rate 1 1 msps max see the serial interface section
ad7475/ad7495 rev. b | page 6 of 24 parameter a version 1 b version 1 unit test conditions/comments power requirements v dd 2.7/5.25 2.7/5.25 v min/max v drive 2.7/5.25 2.7/5.25 v min/max i dd digital inputs = 0 v or v drive normal mode (static) 1 1 ma typ v dd = 2.7 v to 5.25 v, sclk on or off normal mode (operational) 2.6 2.6 ma max v dd = 4.75 v to 5.25 v, f sample = 1 msps 2 2 ma max v dd = 2.7 v to 3.6 v, f sample = 1 msps partial power-down mode 650 650 a typ f sample = 100 ksps partial power-down mode 230 230 a max static full power-down mode 1 1 a max static, sclk on or off power dissipation 3 normal mode (operational) 13 13 mw max v dd = 5 v, f sample = 1 msps 6 6 mw max v dd = 3 v, f sample = 1 msps partial power-down (static) 1.15 1.15 mw max v dd = 5 v 690 690 w max v dd = 3 v full power-down 5 5 w max v dd = 5 v 3 3 w max v dd = 3 v 1 temperature ranges for a, b versions: ?40 c to +85c. 2 guaranteed by initial characterization. 3 see the power vs. throughput rate section.
ad7475/ad7495 rev. b | page 7 of 24 timing specifications 1 v dd = 2.7 v to 5.25 v, v drive = 2.7 v to 5.25 v, ref in = 2.5 v (ad7475), t a = t min to t max , unless otherwise noted. table 3. parameter limit at t min , t max unit description f sclk 2 10 khz min 20 mhz max t convert 16 t sclk t sclk = 1/f sclk 800 ns max f sclk = 20 mhz t quiet 100 ns min minimum quiet time required between conversions t 2 10 ns min cs to sclk setup time t 3 3 22 ns max delay from cs until sdata three-state disabled t 4 40 ns max data access time after sclk falling edge t 5 0.4 t sclk ns min sclk low pulse width t 6 0.4 t sclk ns min sclk high pulse width t 7 10 ns min sclk to data valid hold time t 8 4 10 ns min sclk falling edge to sdata high impedance 45 ns max sclk falling edge to sdata high impedance t 9 20 ns max cs rising edge to sdata high impedance t power-up 20 s max power-up time from full power-down (ad7475) 650 s max power-up time from full power-down (ad7495) 1 guaranteed by initial characterization. all input signa ls are specified with tr = tf = 5 ns (10% to 90% of v drive ) and timed from a voltage level of 1.6 v. 2 mark/space ratio for the sc lk input is 40/60 to 60/40. 3 measured with the load circuit of figure 4 and defined as the time required for the output to cross 0.8 v or 2.0 v. 4 t 8 and t 9 are derived from the measured time taken by the data outputs to change 0.5 v when loaded with the circuit of figure 4. the mea sured number is extrapolated back to remove the effects of charging or discharging the 50 pf capacitor. this means that the times, t 8 and t 9 , quoted in the timing characteristics are the true bus relinquish times of the part and are independent of the bus loading.
ad7475/ad7495 rev. b | page 8 of 24 timing example 1 with f sclk = 20 mhz and a throughput of 1 msps, the cycle time is t 2 + 12.5(1/f sclk ) + t acq = 1 s. with t 2 = 10 ns min, t acq is 365 ns. the 365 ns satisfies the requirement of 300 ns for t acq . in figure 3 , t acq comprises 2.5(1/f sclk ) + t 8 + t quiet , where t 8 = 45 ns. this allows a value of 195 ns for t quiet , satisfying the minimum requirement of 100 ns. timing example 2 with f sclk = 5 mhz and a throughput of 315 ksps, the cycle time is t 2 + 12.5(1/f sclk ) + t acq = 3.174 s. with t 2 = 10 ns min, t acq is 664 ns. the 664 ns satisfies the requirement of 300 ns for t acq . in figure 3 , t acq comprises 2.5(1/f sclk ) + t8 + t quiet , where t8 = 45 ns. this allows a value of 119 ns for t quiet , satisfying the minimum requirement of 100 ns. as in this example and with other slower clock values, the signal may already be acquired before the conversion is complete, but it is still necessary to leave 100 ns minimum t quiet between conversions. in example 2, the signal should be fully acquired at approximately point c in figure 3 . sclk 1 5 13 15 sdata four leading zeros three-state t 4 2 3 16 t 5 t 3 t quiet t convert t 2 three-state db11 db10 db2 db0 t 6 t 7 t 8 14 0 0 00 b db1 01684-b-002 cs 4 figure 2. serial interface timing diagram sclk 1 5 13 15 2 3 16 t 5 t quiet t convert t 2 t 6 t 8 14 b 45ns t acquisition 12.5 (1/f sclk ) 10ns 1/throughput c 01684-b-003 cs 4 figure 3. serial interface timing example 200 a i ol 200 a i oh c l 50pf to output pin 1.6v 01684-b-004 figure 4. load circuit for digital output timing specifications
ad7475/ad7495 rev. b | page 9 of 24 absolute maximum ratings t a = 25c unless otherwise noted. table 4. parameters ratings v dd to gnd ?0.3 v to +7 v v drive to gnd ?0.3 v to +7 v analog input voltage to gnd ?0.3 v to v dd + 0.3 v digital input voltage to gnd ?0.3 v to +7 v v drive to v dd ?0.3 v to v dd + 0.3 v digital output voltage to gnd ?0.3 v to v drive + 0.3 v ref in to gnd ?0.3 v to v dd + 0.3 v input current to any pin except supplies 1 10 ma operating temperature range commercial (a, b version) ?40c to +85c storage temperature range ?65c to +150c junction temperature 150c soic, msop package, power dissipation 450 mw ja thermal impedance 157c/w (soic) 205.9c/w (msop) jc thermal impedance 56c/w (soic) 43.74c/w (msop) lead temperature, soldering vapor phase (60 sec) 215c infrared (15 sec) 220c esd 4 kv 1 transient currents of up to 100 ma do not cause scr latch-up. stresses above those listed under absolute maximum ratings may cause permanent 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 conditions for extended periods may affect device reliability. esd caution esd (electrostatic discharge) sensiti ve device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge wi thout detection. although this product features proprietary esd protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
ad7475/ad7495 rev. b | page 10 of 24 pin configuration and fu nction descriptions top view (not to scale) 8 7 6 5 1 2 3 4 ref in v in gnd v dd v drive sdata sclk ad7475 cs 01684-b-005 figure 5. ad7475 soic/msop pin configuration top view (not to scale) 8 7 6 5 1 2 3 4 ref out v in gnd v dd v drive sdata sclk ad7495 cs 01684-b-006 figure 6. ad7495 soic/msop pin configuration table 5. pin descriptions pin no. mnemonic function 1 (ad7475) ref in reference input for the ad7475. an exte rnal reference must be applied to this input. the voltage range for the external reference is 2.5 v 1% for specified performa nce. a cap of a least 0.1 f should be placed on the ref in pin. 1 (ad7495) ref out reference output for the ad7495. a minimum 100 nf capaci tance is required from this pin to gnd. the internal reference can be taken from this pin, but buffering is required before it is applied elsewhere in a system. 2 v in analog input. single-ended analog input channel. the input range is 0 to ref in. 3 gnd analog ground. ground reference point for all circuitry on the ad7475/ad7495. all analog input signals and any external reference signal should be referred to this gnd voltage. 4 sclk serial clock, logic input. sclk provid es the serial clock for accessing data from the part. this clock input is also used as the clock source for the ad7475/ad7495 conversion process. 5 sdata data out, logic output. the conversi on result from the ad7475/ad7495 is prov ided on this output as a serial data stream. the bits are clocked out on the falling edge of the sclk input. the data stream consists of four leading zeros followed by the 12 bits of con version data, which is provided msb first. 6 v drive logic power supply input. the voltage supplied at this pin determines the operating voltage for the serial interface of the ad7475/ad7495. 7 cs chip select, active low logic input. th is input provides the dual function of initiating conversions on the ad7475/ad7495 and also frames the serial data transfer. 8 v dd power supply input. the v dd range for the ad7475/ad7495 is from 2.7 v to 5.25 v.
ad7475/ad7495 rev. b | page 11 of 24 ) terminology integral nonlinearity the maximum deviation from a straight line passing through the endpoints of the adc transfer function. the endpoints of the transfer function are zero scale, a point ? lsb below the first code transition, and full scale, a point ? lsb above the last code transition. differential nonlinearity the difference between the measured and the ideal 1 lsb change between any two adjacent codes in the adc. offset error the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, that is, agnd + 0.5 lsb. gain error this is the deviation of the last code transition (111. . . 110) to (111. . . 111) from the ideal (that is, v ref ? 1.5 lsb) after the offset error has been adjusted out. track-and-hold acquisition time the track-and-hold amplifier returns into track mode on the 13 th sclk rising edge (see the serial interface section). the track-and-hold acquisition time is the minimum time required for the track-and-hold amplifier to remain in track mode for its output to reach and settle to within 0.5 lsb of the applied input signal, given a step change to the input signal. signal-to-noise and distortion ratio (sinad) the measured ratio of signal-to-noise and distortion at the output of the analog-to-digital converter (adc). the signal is the rms amplitude of the fundamental. noise is the sum of all nonfundamental signals up to half the sampling frequency (f s /2), excluding dc. the ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. the theoretical sinad ratio for an ideal n-bit converter with a sine wave input is given by () ( db76.102.6 += + n distortion noisetosignal for a 12-bit converter, the sinad is 74 db. total harmonic distortion (thd) the ratio of the rms sum of harmonics to the fundamental. for the ad7475/ad7495, thd is defined as () 1 65432 v vvvvv thd 22222 log20db ++++ = 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 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 determined by the largest harmonic in the spectrum, but for adcs where the harmonics are buried in the noise floor, it is a noise peak. intermodulation distortion with inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities creates distortion products at sum and difference frequencies of mfa nfb where m, n = 0, 1, 2, 3, etc. intermodulation distortion terms are those for which neither m nor n is 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). the ad7475/ad7495 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-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. like thd, intermodulation distortion is calculated as the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals, expressed in dbs.
ad7475/ad7495 rev. b | page 12 of 24 typical performance curves figure 7 shows a typical fft plot for the ad7475 at a 1 mhz sample rate and a 100 khz input frequency. frequency (khz) ?115 0 sinad (db) 50 100 150 200 250 300 ?95 ?75 ?55 ?35 350 400 500450 ?15 8192 point fft f sample = 1msps f in = 100khz sinad = 70.46db thd = ?87.7db sfdr = ?89.5db 01684-b-007 figure 7. ad7475 dynamic performance figure 8 shows a typical fft plot for the ad7495 at a 1 mhz sample rate and a 100 khz input frequency. frequency (khz) ?115 0 sinad (db) 50 100 150 200 250 300 ?95 ?75 ?55 ?35 350 400 500450 ?15 8192 point fft f sample = 1msps f in = 100khz sinad = 69.95db thd = ?89.2db sfdr = ?91.2db 01684-b-008 figure 8. ad7495 dynamic performance figure 9 shows the sinad performance vs. input frequency for various supply voltages while sampling at 1 msps with an sclk of 20 mhz. input frequency (khz) 68.5 sinad (db) 10 100 69.0 69.5 70.0 70.5 1000 71.0 v dd = v drive = 5.25v v dd = v drive = 3.60v v dd = v drive = 2.70v v dd = v drive = 4.75v 01684-b-009 figure 9. ad7495 sinad vs. input frequency at 1 msps
ad7475/ad7495 rev. b | page 13 of 24 theory of operation the ad7475/ad7495 are fast, micropower, 12-bit, single- supply analog-to-digital converters (adcs). the parts can be operated from a 2.7 v to 5.25 v supply. when operated from either a 5 v supply or a 3 v supply, the ad7475/ad7495 are capable of throughput rates of 1 msps when provided with a 20 mhz clock. the ad7475/ad7495 adcs have an on-chip track-and-hold with a serial interface housed in either an 8-lead soic_n or mini_so package, features that offer the user considerable space-saving advantages over alternative solutions. the ad7495 also has an on-chip 2.5 v reference. the serial clock input accesses data from the part but also provides the clock source for the successive-approximation adc. the analog input range is 0 v to ref in for the ad7475 and 0 v to ref out for the ad7495. the ad7475/ad7495 also feature power-down options to allow power saving between conversions. the power-down feature is implemented across the standard serial interface, as described in the operating modes section. converter operation the ad7475/ad7495 are 12-bit, successive approximation analog-to-digital converters based around a capacitive dac. the ad7475/ad7495 can convert analog input signals in the range 0 v to 2.5 v. figure 10 and figure 12 show simplified schematics of the adc. the adc comprises control logic, sar, and a capacitive dac, which are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition. figure 10 shows the adc during its acquisition phase. sw2 is closed and sw1 is in position a. the comparator is held in a balanced condition and the sampling capacitor acquires the signal on v in . comparator v in control logic capacitive dac agnd 4k sw2 sw1 a b 01684-b-010 figure 10. adc acquisition phase when the adc starts a conversion (see figure 11), sw2 opens and sw1 moves to position b causing the comparator to become unbalanced. the control logic and the capacitive dac are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition. when the comparator is rebalanced, the conversion is complete. the control logic generates the adc output code. comparator v in control logic capacitive dac agnd 4k sw2 sw1 a b 01684-b-011 figure 11. adc conversion phase adc transfer function the output coding of the ad7475/ad7495 is straight binary. the designed code transitions occur midway between successive lsb integer values (that is, ? lsb, 3 / 2 lsbs, etc.). the lsb size is = v ref /4096. the ideal transfer characteristic for the ad7475/ad7495 is shown in figure 12 . 111...111 111...110 111...000 011...111 000...010 000...001 000...000 adc code 0v 0.5lsb v ref ?1.5lsb analog input 1lsb = v ref /4096 01684-b-012 figure 12. ad7475/ad7495 transfer characteristic
ad7475/ad7495 rev. b | page 14 of 24 typical connection diagram figure 13 and figure 15 show typical connection diagrams for the ad7475 and ad7495, respectively. in both setups the gnd pin is connected to the analog ground plane of the system. in figure 13 , ref in is connected to a decoupled 2.5 v supply from a reference source, the ad780, to provide an analog input range of 0 v to 2.5 v. although the ad7475 is connected to a v dd of 5 v, the serial interface is connected to a 3 v micro- processor. the v drive pin of the ad7475 is connected to the same 3 v supply of the microprocessor to allow a 3 v logic interface (see the digital inputs section.) in figure 15 , the ref out pin of the ad7495 is connected to a buffer and then applied to a level-shifting circuit used on the analog input to allow a bipolar signal to be applied to the ad7495. a minimum 100 nf capacitance is required on the ref out pin to gnd. the conversion result from both adcs is output in a 16-bit word with four leading zeros followed by the msb of the 12-bit result. for applications where power consumption is of concern, the power-down modes should be used between conversions or bursts of several conversions to improve power performance. see the operating modes section for more information. v dd v in gnd 5v supply 2.5v ad780 3v supply ad7475 0v to 2.5v input sdata c/ p sclk serial interface 0.1 f (min) v drive ref in 0.1 f 10 f 0.1 f 10 f cs 01684-b-013 figure 13. ad7475 typical connection diagram analog input figure 14 shows an equivalent circuit of the analog input structure of the ad7475/ad7495. the d1 and d2 diodes 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 causes these diodes to become forward-biased and start conducting current into the substrate. the maximum current these diodes can conduct without causing irreversible damage to the part is 20 ma. the capacitor c1 in figure 14 is typically about 4 pf and can primarily be attributed to pin capacitance. the resistor r1 is a lumped component made up of the on resistance of a switch. this resistor is typically about 100 . the capacitor c2 is the adc sampling capacitor and has a capacitance of 16 pf, typically. for ac applications, it is recommended to remove high frequency components from the analog input signal using an rc low-pass filter on the relevant analog input pin. in applications where harmonic distortion and signal-to-noise ratio are critical, the analog input should be driven from a low impedance source. large source impedances significantly affect the ac performance of the adc. this may necessitate the use of an input buffer amplifier. the choice of the op amp is a function of the particular application. r1 v in c2 16pf d1 d2 c1 4pf v dd conversion phase: switch open track phase: switch closed 01684-b-014 figure 14. equivalent analog input circuit v dd v in gnd 5v supply 3v supply ad7495 0v to 2.5v input sdata c/ p sclk serial interface 0.1 f (min) v drive ref out 0.1 f 10 f 0.1 f 10 f r r 3r r v 0v v cs 01684-b-015 figure 15. ad7495 typical connection diagram
ad7475/ad7495 rev. b | page 15 of 24 when no amplifier is used to drive the analog input, the source impedance should be limited to low values. the maximum source impedance depends on the amount of total harmonic distortion (thd) that can be tolerated. the thd increases as the source impedance increases and performance degrades. figure 16 shows a graph of the total harmonic distortion vs. source impedance for various analog input frequencies. source impedance ( ) ?90 thd (db) 1 100 ?80 ?70 ?60 ?50 10000 ?40 f in = 500khz f in = 10khz f in = 100khz f in = 200khz 10 1000 ?30 ?20 ?10 01684-b-016 figure 16. thd vs. source impedance for various analog input frequencies figure 17 shows a graph of total harmonic distortion vs. analog input frequency for various supply voltages while sampling at 1 msps with an sclk of 20 mhz. input frequency (khz) thd (db) 10 100 ?95 ?93 ?91 ?87 1000 ?85 v dd = v drive = 3.60v v dd = v drive = 2.70v v dd = v drive = 5.25v v dd = v drive = 4.75v ?83 ?81 ?79 ?77 ?75 ?89 01684-b-017 figure 17. thd vs. analog input frequency for various supply voltages digital inputs the digital inputs applied to the ad7475/ad7495 are not limited by the maximum ratings, which limit the analog inputs. instead, the digital inputs applied can go to 7 v and are not restricted by the v dd + 0.3 v limit as on the analog inputs. another advantage of sclk and cs not being restricted by the v dd + 0.3 v limit is that power supply sequencing issues are avoided. if cs or sclk are applied before v dd , there is no risk of latch-up as there would be on the analog inputs if a signal greater than 0.3 v were applied prior to v dd . v drive the ad7475/ad7495 also has the v drive feature. this feature controls the voltage at which the serial interface operates. v drive allows the adc to easily interface to both 3 v and 5 v processors. for example, if the ad7475/ad7495 were operated with a v dd of 5 v, the v drive pin could be powered from a 3 v supply. the ad7475/ad7495 have better dynamic performance with a v dd of 5 v, while still being able to interface to 3 v digital parts. care should be taken to ensure v drive does not exceed v dd by more than 0.3 v. (see the absolute maximum ratings section.) reference section an external reference source should be used to supply the 2.5 v reference to the ad7475. errors in the reference source result in gain errors in the ad7475 transfer function and add the specified full-scale errors on the part. the ad7475 voltage reference input, ref in, has a dynamic input impedance. a small dynamic current is required to charge the capacitors in the capacitive dac during the bit trials. this current is typically 50 a for a 2.5 v reference. a capacitor of at least 0.1 f should be placed on the ref in pin. suitable reference sources for the ad7475 are the ad780, ad680, ad1582, adr391, adr381, adr431, and adr03. the ad7495 contains an on-chip 2.5 v reference. as shown in figure 18, the voltage that appears at the ref out pin is internally buffered before being applied to the adc; the output impedance of this buffer is typically 10 . the reference is capable of sourcing up to 2 ma. the ref out pin should be decoupled to agnd using a 100 nf or greater capacitor. if the 2.5 v internal reference is used to drive another device that is capable of glitching the reference at critical times, then the reference has to be buffered before driving the device. to ensure optimum performance of the ad7495, it is recom- mended that the internal reference not be over driven. if an adc with external reference capability is required, the ad7475 should be used. v ref out 25 40k 160k 01684-b-018 figure 18. ad7495 reference circuit
ad7475/ad7495 rev. b | page 16 of 24 operating modes the ad7475/ad7495 operating mode is selected by controlling the logic state of the cs signal during a conversion. there are three possible modes of operation: normal mode, partial power- down mode, and full power-down mode. the point at which cs is pulled high after the conversion has been initiated determines which power-down mode, if any, the device enters. similarly, if already in a power-down mode, cs can control whether the device returns to normal operation or remains in power-down. these modes of operation are designed to provide flexible power management options. these options can be chosen to optimize the power dissipation/throughput rate ratio for differing application requirements. normal mode this mode is intended for fastest throughput rate performance, because the user does not have to worry about any power-up times with the ad7475/ad7495 remaining fully powered all the time. figure 19 shows the general diagram of the ad7475/ ad7495 operating in this mode. the conversion is initiated on the falling edge of cs , as described in the serial interface section. to ensure the part remains fully powered-up at all times, cs must remain low until at least 10 sclk falling edges have elapsed after the falling edge of cs . if cs is brought high any time after the 10 th sclk falling edge, but before the 16 th sclk falling edge, the part remains powered up but the conversion is terminated and sdata goes back into three-state. sixteen serial clock cycles are required to complete the conversion and access the conversion result. cs may idle high until the next conversion or may idle low until sometime prior to the next conversion (effectively idling cs low). once a data transfer is complete (sdata has returned to three- state), another conversion can be initiated after the quiet time, t quiet , has elapsed, by bringing cs low again. partial power-down mode this mode is intended for use in applications where slower throughput rates are required; either the adc is powered down between each conversion, or a series of conversions may be performed at a high throughput rate and then the adc is powered down for a relatively long duration between these bursts of several conversions. when the ad7475 is in partial power-down, all analog circuitry is powered down except for the bias current generator; and, in the case of the ad7495, all analog circuitry is powered down except for the on-chip reference and reference buffer. to enter partial power-down, the conversion process must be interrupted by bringing cs high anywhere after the second falling edge of sclk and before the tenth falling edge of sclk, as shown in figure 20 . once cs has been brought high in this window of sclks, the part enters partial power-down, the conversion that was initiated by the falling edge of cs is terminated, and sdata goes back into three-state. if cs is brought high before the second sclk falling edge, the part remains in normal mode and does not power down. this avoids accidental power-down due to glitches on the cs line. sclk four leading zeros + conversion result sdata 1 16 10 cs 01684-b-019 figure 19. normal mode sclk 1 16 10 2 cs 01684-b-020 figure 20. entering partial power-down mode
ad7475/ad7495 rev. b | page 17 of 24 to exit this operating mode and power up the ad7475/ad7495 again, a dummy conversion is performed. on the falling edge of cs , the device begins to power up and continues to power up as long as cs is held low until after the falling edge of the tenth sclk. the device is fully powered up once 16 sclks have elapsed, and valid data results from the next conversion, as shown in figure 21 . if cs is brought high before the second falling edge of sclk, the ad7475/ad7495 go back into partial power-down again. this avoids accidental power-up due to glitches on the cs line; although the device may begin to power up on the falling edge of cs , it powers down again on the rising edge of cs . if in partial power-down and cs is brought high between the second and tenth falling edges of sclk, the device enters full power-down mode. power-up time the power-up time of the ad7475/ad7495 from partial power-down is typically 1 s, which means that with any frequency of sclk up to 20 mhz, one dummy cycle is sufficient to allow the device to power up from partial power- down. once the dummy cycle is complete, the adc is fully powered up and the input signal is acquired properly. the quiet time, t quiet, must still be allowed from the point where the bus goes back into three-state after the dummy conversion to the next falling edge of cs . when running at a 1 msps throughput rate, the ad7475/ad7495 power up and acquire a signal within 0.5 lsb in one dummy cycle, 1 s. when powering up from the power-down mode with a dummy cycle, as in figure 21 , the track-and-hold that was in hold mode while the part was powered down returns to track mode after the first sclk edge the part receives after the falling edge of cs . this is shown as point a in figure 21. although at any sclk frequency one dummy cycle is sufficient to power up the device and acquire v in , it does not necessarily mean that a full dummy cycle of 16 sclks must always elapse to power up the device and fully acquire v in ; 1 s is sufficient to power up the device and acquire the input signal. if, for example, a 5 mhz sclk frequency were applied to the adc, the cycle time would be 3.2 s. in one dummy cycle, 3.2 s, the part would be powered up and v in fully acquired. however, after 1 s with a 5 mhz sclk, only 5 sclk cycles would have elapsed. at this stage, the adc would be fully powered up and the signal acquired. in this case, the cs can be brought high after the tenth sclk falling edge and brought low again after a time, t quiet, to initiate the conversion. full power-down mode full power-down mode is intended for use in applications where slower throughput rates are required than that in the partial power-down mode, because power up from a full power- down would not be complete in just one dummy conversion. this mode is more suited to applications where a series of conversions performed at a relatively high throughput rate are followed by a long period of inactivity and therefore power down. when the ad7475/ad7495 are in full power-down, all analog circuitry is powered down. sclk sdata invalid data valid data 1 10 16 1 the part begins to power up the part is fully powered up 16 a cs 01684-b-021 figure 21. exiting partial power-down mode sclk sdata invalid data invalid data 1 10 16 1 the part begins to power up 16 2 10 2 the part enters full power-down the part enters partial power-down three-state three-state 01684-b-023 cs figure 22. entering full power-down mode
ad7475/ad7495 rev. b | page 18 of 24 full power-down is entered in a way similar to partial power- down, except the timing sequence shown in figure 20 must be executed twice. the conversion process must be interrupted in a similar fashion by bringing cs high anywhere after the second falling edge of sclk and before the tenth falling edge of sclk. the device enters partial power-down at this point. to reach full power-down, the next conversion cycle must be interrupted in the same way, as shown in figure 22 . once cs has been brought high in this window of sclks, then the part powers down completely. note that it is not necessary to complete the 16 sclks once cs has been brought high to enter a power-down mode. to exit full power-down, and power up the ad7475/ad7495 again, a dummy conversion is performed as when powering up from partial power-down. on the falling edge of cs , the device begins to power up and continues to power up as long as cs is held low until after the falling edge of the tenth sclk. the power-up time is longer than one dummy conversion cycle however, and this time, t power-up, must elapse before a conversion can be initiated, as shown in figure 23 . see the timing specifications section for more information. when power supplies are first applied to the ad7475/ad7495, the adc may power up in either of the power-down modes or normal mode. because of this, it is best to allow a dummy cycle to elapse to ensure the part is fully powered up before attempting a valid conversion. likewise, if the intent is to keep the part in partial power-down mode immediately after the supplies are applied, then two dummy cycles must be initiated. the first dummy cycle must hold cs low until after the tenth sclk falling edge, as shown in figure 19 . in the second cycle, cs must be brought high before the tenth sclk edge, but after the second sclk falling edge, as shown in figure 20 . alternatively, if the intent is to place the part in full power- down mode when the supplies have been applied, then three dummy cycles must be initiated. the first dummy cycle must hold cs low until after the tenth sclk edge, as shown in figure 19 ; the second and third dummy cycle place the part in full power-down, as shown in figure 22 . (see the operating modes section.) once supplies are applied to the ad7475, enough time must be allowed for the external reference to power up and charge the reference capacitor to its final value. for the ad7495, enough time should be allowed for the internal reference buffer to charge the reference capacitor. then, to place the ad7475/ ad7495 in normal mode, a dummy cycle, 1 s, should be initiated. if the first valid conversion is then performed directly after the dummy conversion, ensure that adequate acquisition time has been allowed. as mentioned earlier, when powering up from the power-down mode, the part returns to track upon the first sclk edge applied after the falling edge of cs . however, when the adc powers up initially after supplies are applied, the track-and-hold is already in track. this means (assuming one has the facility to monitor the adc supply current) if the adc powers up in the desired mode of operation, and a dummy cycle is not required to change mode, then neither is a dummy cycle required to place the track-and- hold into track. if no current monitoring facility is available, the relevant dummy cycle(s) should be performed to ensure the part is in the required mode. sclk sdata invalid data valid data 1 10 16 1 the part begins to power up the part is fully powered up 16 t power-up 01684-b-022 cs figure 23. exiting full power-down mode
ad7475/ad7495 rev. b | page 19 of 24 power vs. throughput rate by using the partial power-down mode on the ad7475/ ad7495 when not converting, the average power consumption of the adc decreases at lower throughput rates. figure 24 shows how, as the throughput rate is reduced, the part remains in its partial power-down state longer and the average power consumption over time drops accordingly. throughput (ksps) 100 0.001 0 power (mw) 50 100 0.01 0.1 1 10 150 200 250 300 350 ad7495 5v sclk = 20mhz ad7495 3v sclk = 20mhz ad7475 5v sclk = 20mhz ad7475 3v sclk = 20mhz 01684-b-025 figure 24. power vs. throughput for partial power down for example, if the ad7495 is operated in a continuous sampling mode with a throughput rate of 100 ksps and an sclk of 20 mhz (v dd = 5 v), and the device is placed in partial power-down mode between conversions, then the power consumption is calculated as follows. the maximum power dissipation during normal operation is 13 mw (v dd = 5 v). if the power-up time from partial power-down is one dummy cycle, that is, 1 s, and the remaining conversion time is another cycle, that is, 1 s, then the ad7495 can be said to dissipate 13 mw for 2 s during each conversion cycle. for the remainder of the conversion cycle, 8 s, the part remains in partial power-down mode. the ad7495 dissipates 1.15 mw for the remaining 8 s of the conversion cycle. if the throughput rate is 100 ksps, and the cycle time is 10 s, the average power dissipated during each cycle is (2/10) (13 mw) + (8/10) (1.15 mw) = 3.52 mw. if v dd = 3 v, sclk = 20 mhz and the device is again in partial power-down mode between conver- sions, the power dissipated during normal operation is 6 mw. the ad7495 dissipates 6 mw for 2 s during each conversion cycle and 0.69 mw for the remaining 8 s where the part is in partial power-down. with a throughput rate of 100 ksps, the average power dissipated during each conversion cycle is (2/10) (6 mw) + (8/10) (0.69 mw) = 1.752 mw. figure 24 shows the power vs. throughput rate when using partial power-down mode between conversions with both 5 v and 3 v supplies for both the ad7475 and ad7495. for the ad7475, partial power- down current is lower than that of the ad7495. full power-down mode is intended for use in applications with slower throughput rates than required for partial power-down mode. it is necessary to leave 650 s for the ad7495 to be fully powered up from full power-down before initiating a conver- sion. current consumptions between conversions is typically less than 1 a. figure 25 shows a typical graph of current vs. throughput for the ad7495 while operating in different modes. at slower throughput rates, for example, 10 sps to 1 ksps, the ad7495 was operated in full power-down mode. as the throughput rate increased, up to 100 ksps, the ad7495 was operated in partial power-down mode, with the part being powered down between conversions. with throughput rates from 100 ksps to 1 msps, the part operated in normal mode, remaining fully powered up at all times. throughput (sps) 2.0 10 current (ma) 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 100 1k 10k 100k 1m v dd = 5v full power-down partial power-down normal 01684-b-026 figure 25. typical ad7495 current vs. throughput
ad7475/ad7495 rev. b | page 20 of 24 serial interface figure 26 shows the detailed timing diagram for serial inter- facing to the ad7475/ad7495. the serial clock provides the conversion clock and also controls the transfer of information from the ad7475/ad7495 during conversion. cs initiates the data transfer and conversion process. the falling edge of cs puts the track-and-hold into hold mode and takes the bus out of three-state. the analog input is sampled at this point. the conversion is also initiated at this point and requires 16 sclk cycles to complete. once 13 sclk falling edges have elapsed, the track-and-hold goes back into track on the next sclk rising edge, as shown in figure 26 at point b. on the 16th sclk falling edge, the sdata line goes back into three-state. if the rising edge of cs occurs before 16 sclks have elapsed, the conversion is terminated and the sdata line goes back into three-state, as shown in figure 27 ; otherwise sdata returns to three-state on the 16th sclk falling edge, as shown in figure 26 . sixteen serial clock cycles are required to perform the con- version process and to access data from the ad7475/ad7495. cs going low provides the first leading zero to be read in by the microcontroller or dsp. the remaining data is then clocked out by subsequent sclk falling edges beginning with the second leading zero; thus the first falling clock edge on the serial clock has the second leading zero provided. the final bit in the data transfer is valid on the 16 th falling edge, having been clocked out on the previous (15 th ) falling edge. in applications with a slower sclk, it may be possible to read in data on each sclk rising edge, although the first leading zero still has to be read on the first sclk falling edge after the cs falling edge. therefore, the first rising edge of sclk after the cs falling edge provides the second leading zero and the 15th rising sclk edge has db0 provided. this method may not work with most microprocessors/dsps, but could possibly be used with fpgas and asics. sclk 1 5 13 15 sdata four leading zeros three-state t 4 2 3 16 t 5 t 3 t quiet t convert t 2 three-state db11 db10 db2 db0 t 6 t 7 t 8 14 0 0 00 b db1 4 01684-b-027 cs figure 26. serial interface timing diagram sclk 1 5 13 15 sdat a four leading zeros three-state t 4 2 3 16 t 9 t 3 t quiet t convert t 2 three-state db11 db10 db2 t 6 t 7 14 0 0 0 0 b 4 01684-b-028 cs figure 27. serial interface timing diagram conversion termination
ad7475/ad7495 rev. b | page 21 of 24 microprocessor interfacing the serial interface on the ad7475/ad7495 allows the parts to be directly connected to a range of many different micro- processors. this section explains how to interface the ad7475/ ad7495 with some of the more common microcontroller and dsp serial interface protocols. ad7475/ad7495 to tms320c5 x /c54 x the serial interface on the tms320c5x/c54x uses a continuous serial clock and frame synchronization signals to synchronize the data transfer operations with peripheral devices like the ad7475/ad7495. the cs input allows easy interfacing between the tms320c5x/c54x and the ad7475/ad7495 without any glue logic required. the serial port of the tms320c5x/c54x is set up to operate in burst mode with internal clkx (tx serial clock) and fsx (tx frame sync). the serial port control register (spc) must have the following setup: fo = 0, fsm = 1, mcm = 1, and txm = 1. the format bit, fo, may be set to 1 to set the word length to 8 bits, in order to implement the power-down modes on the ad7475/ad7495. the connection diagram is shown in figure 28 . note that for signal processing applications, it is imperative that the frame synchronization signal from the tms320c5x/c54x provide equidistant sampling. the v drive pin of the ad7475/ad7495 takes the same supply voltage as that of the tms320c5x/c54x. this allows the adc to operate at a higher voltage than the serial interface, that is, tms320c5x/c54x, if necessary. ad7475/ad7495* sclk * additional pins omitted for clarity clkx dr fbx fsr sdata v drive v dd tms320c5x/c54x* clkr 01684-b-029 cs figure 28. interfacing to the tms320c5x/54x ad7475/ad7495 to adsp-21 xx the adsp-21xx family of dsps is interfaced directly to the ad7475/ad7495 without any glue logic required. the v drive pin of the ad7475/ad7495 takes the same supply voltage as that of the adsp-21xx. this allows the adc to operate at a higher voltage than the serial interface, that is, adsp-21xx, if necessary. the sport control register should be set up as shown in table 6 . table 6. sport control register bits function tfsw = rfsw = 1 alternate framing invrfs = invtfs = 1 active low frame signal dtype = 00 right-justify data slen = 1111 16-bit data words isclk = 1 internal serial clock tfsr = rfsr = 1 frame every word irfs = 0 itfs = 1 to implement the power-down modes, slen should be set to 1001 to issue an 8-bit sclk burst. the connection diagram is shown in figure 29 . the adsp-21xx has the tfs and rfs of the sport tied together, with tfs set as an output and rfs set as an input. the dsp operates in alternate framing mode and the sport control register is set up as described. the frame synchronization signal generated on the tfs is tied to cs and, as with all signal processing applications, equidistant sampling is necessary. however, in this example, the timer interrupt is used to control the sampling rate of the adc and, under certain conditions, equidistant sampling may not be achieved. ad7475/ad7495* sclk * additional pins omitted for clarity dr rfs tfs sdata v drive v dd adsp-21xx* sclk 01684-b-030 cs figure 29. interfacing to the adsp-21xx
ad7475/ad7495 rev. b | page 22 of 24 the timer registers are loaded with a value that provides an interrupt at the required sample interval. when an interrupt is received, a value is transmitted with tfs/dt (adc control word). the tfs is used to control the rfs, and therefore, the reading of data. the frequency of the serial clock is set in the sclkdiv register. when the instruction to transmit with tfs is given, (that is, ax0 = tx0), the state of the sclk is checked. the dsp waits until the sclk has gone high, low, and high before transmission starts. if the timer and sclk values are chosen such that the instruction to transmit occurs on or near the rising edge of sclk, the data can be transmitted or it can wait until the next clock edge. for example, the adsp-2111 has a master clock frequency of 16 mhz. if the sclkdiv register is loaded with the value 3, an sclk of 2 mhz is obtained, and eight master clock periods elapse for every one sclk period. if the timer registers are loaded with the value 803, 100.5 sclks occur between interrupts and subsequently between transmit instructions. this situation results in nonequidistant sampling because the transmit instruction is occurring on a sclk edge. if the number of sclks between interrupts is a whole integer figure of n, equidistant sampling is implemented by the dsp. ad7475/ad7495 to dsp56 xxx the connection diagram in figure 30 shows how the ad7475/ ad7495 can be connected to the synchronous serial interface (ssi) of the dsp56xxx family of devices from motorola. the ssi is operated in synchronous mode (syn bit in crb = 1) with internally generated 1-bit clock period frame sync for both tx and rx (bits fsl1 = 1 and fsl0 = 0 in crb). set the word length to 16 by setting bits wl1 = 1 and wl0 = 0 in cra. to implement the power-down modes on the ad7475/ad7495, the word length can be changed to 8 bits by setting bit wl1 = 0 and bit wl0 = 0 in cra. for signal processing applications, it is imperative that the frame synchronization signal from the dsp56xxx provide equidistant sampling. the v drive pin of the ad7475/ad7495 takes the same supply voltage as that of the dsp56xxx. this allows the adc to operate at a voltage higher than the serial interface, that is, dsp56xxx, if necessary. ad7475/ad7495* sclk * additional pins omitted for clarity sclk sc2 sdata v drive v dd dsp56xxx* srd 01684-b-031 cs figure 30. interfacing to the dsp56xxx ad7475/ad7495 to mc68hc16 the serial peripheral interface (spi) on the mc68hc16 is configured for master mode (mstr) = 1, clock polarity bit (cpol) = 1, and the clock phase bit (cpha) = 0. the spi is configured by writing to the spi control register (spcr), as described in the 68hc16 user manual. the serial transfer takes place as a 16-bit operation when the size bit in the spcr register is set to size = 1. to implement the power-down modes with an 8-bit transfer, set size = 0. (a connection diagram is shown in figure 31 .) the v drive pin of the ad7475/ad7495 takes the same supply voltage as that of the mc68hc16. this allows the adc to operate at a higher voltage than the serial interface, that is, the mc68hc16, if necessary. ad7475/ad7495* sclk * additional pins omitted for clarity miso/pmc0 ss/pmc3 sdata v drive v dd mc68hc16* sclk/pcm2 01684-b-032 cs figure 31. interfacing to the mc68hc16
ad7475/ad7495 rev. b | page 23 of 24 outline dimensions 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) 4 1 85 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-012-aa figure 32. 8-lead standard small outline package [soic_n] narrow body (r-8) dimensions shown in millimeters and (inches) 0.80 0.60 0.40 8 0 4 8 1 5 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-187-aa figure 33. 8-lead mini small outline package [mini_so] (rm-8) dimensions shown in millimeters
ad7475/ad7495 rev. b | page 24 of 24 ordering guide model range linearity error (lsb) 1 package option 2 branding information ad7475ar ?40c to +85c 1.5 so-8 AD7475AR-REEL ?40c to +85c 1.5 so-8 AD7475AR-REEL7 ?40c to +85c 1.5 so-8 ad7475br ?40c to +85c 1 so-8 ad7475br-reel ?40c to +85c 1 so-8 ad7475br-reel7 ?40c to +85c 1 so-8 ad7475arm ?40c to +85c 1.5 rm-8 c9a ad7475arm-reel ?40c to +85c 1.5 rm-8 c9a ad7475arm-reel7 ?40c to +85c 1.5 rm-8 c9a ad7475brm ?40c to +85c 1 rm-8 c9b ad7475brm-reel ?40c to +85c 1 rm-8 c9b ad7475brm-reel7 ?40c to +85c 1 rm-8 c9b ad7475brmz 3 ?40c to +85c 1 rm-8 c3c ad7475brmz-reel 3 ?40c to +85c 1 rm-8 c3c ad7475brmz-reel7 3 ?40c to +85c 1 rm-8 c3c ad7495ar ?40c to +85c 1.5 so-8 ad7495ar-reel ?40c to +85c 1.5 so-8 ad7495ar-reel7 ?40c to +85c 1.5 so-8 ad7495br ?40c to +85c 1 so-8 ad7495br-reel ?40c to +85c 1 so-8 ad7495br-reel7 ?40c to +85c 1 so-8 ad7495brz 3 ?40c to +85c 1 so-8 ad7495brz-reel 3 ?40c to +85c 1 so-8 ad7495brz-reel7 3 ?40c to +85c 1 so-8 ad7495arm ?40c to +85c 1.5 rm-8 cca ad7495arm-reel ?40c to +85c 1.5 rm-8 cca ad7495arm-reel7 ?40c to +85c 1.5 rm-8 cca ad7495armz 3 ?40c to +85c 1.5 rm-8 c3b ad7495armz-reel 3 ?40c to +85c 1.5 rm-8 c3b ad7495armz-reel7 3 ?40c to +85c 1.5 rm-8 c3b ad7495brm ?40c to +85c 1 rm-8 ccb ad7495brm-reel ?40c to +85c 1 rm-8 ccb ad7495brm-reel7 ?40c to +85c 1 rm-8 ccb eval-ad7495cb 4 evaluation board eval-ad7475cb evaluation board eval-control brd2 5 controller board 1 linearity error here refers to integral linearity error. 2 so = soic; rm = msop. 3 z = pb-free part. 4 this can be used as a standalone evaluation board or in conjunction with the evaluation controller board for evaluation/demons tration purposes. 5 the evaluation board controller is a complete unit allowing a pc to control and communicate with all analog devices evaluation boards ending in the cb designators. ? 2005 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. c01684C0C5/05(b)

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