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16 - bit, 10 msps, pulsar differential adc data sheet ad7626 rev. d document feedback 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 change 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 ? 2009 C 2016 analog devices, inc. all rights reserved. technical support www.analog.com features throughput: 10 msps snr: 91.5 db 16- b it n o m issing codes inl: 0. 45 lsb dnl: 0.3 5 lsb power dissipation: 136 mw 32- lead lfcsp (5 mm 5 mm) sar architecture no latency/pipeline delay 16- bit resolution with no missing codes zero error: 1 lsb differential input rang e: 4.0 96 v serial lvds interface self clocked mode echoed clock mode lvds or cmos option for conversion control (cnv signal) reference options internal : 4 .096 v external (1.2 v) buffered to 4.096 v exter nal: 4.096 v applications digital i maging systems digital x - ray digital mri ccd and ir c ameras high speed data acquisition high dynamic range telecommunications receivers spectrum analysis test equipment functional block dia gram ad7626 clock logic serial lvds in? in+ refin ref vcm sar 2 cnv+, cnv? vio d+, d? dco+, dco? clk+, clk? 1.2v band gap cap dac 07648-001 figure 1. general description the ad7626 is a 16 - bit, 10 msps , charge redistribution successive approximation register (sar) based architecture analog - to - digital converter (adc). sar architecture allows unmatched performance bot h in noise ( 9 1.5 db snr ) and in linearity ( 0.45 lsb inl ) . th e ad7626 contains a high speed , 16- bit sampling adc, an internal conversion clock, and an internal buffered reference. on the cnv edge, it samples the voltage difference between the in+ and in ? pins. the voltages on these pins swing in opposite phase between 0 v and ref. the 4.096 v reference voltage, ref, can be generated internally or applied externally. all converted results are available on a single low voltage differential signaling ( lvds ) self clocked or echoed clock serial interface , reducing external hardware connections . the ad7626 is housed in a 32 - lead , 5 mm 5 mm lfcsp with operation specified from ?40c to +85c. table 1 . fast pulsar ? adc selection input type resolution (bits) 1 msps to <2 msps 2 msps to 3 msps 5 msps to 6 msps 10 msps differential (ground sense) 16 ad7653 ad7985 ad7667 ad7980 ad7983 true bipolar 16 ad7671 differential (antiphase) 16 ad7677 ad7621 ad7625 ad7626 ad7623 ad7622 ad7961 differential (antiphase) 18 ad7643 ad7641 ad7960 ad7982 ad7986 ad7984
ad7626* product page quick links last content update: 06/09/2017 comparable parts view a parametric search of comparable parts. evaluation kits ? ad7626 evaluation kit documentation application notes ? an-742: frequency domain response of switched- capacitor adcs ? an-931: understanding pulsar adc support circuitry data sheet ? ad7626: 16-bit, 10 msps, pulsar differential adc data sheet technical books ? the data conversion handbook, 2005 user guides ? ug-745: evaluating the ad7625/ad7626 16-bit, 6 msps/ 10 msps pulsar differential adc tools and simulations ? ad7625/ad7626 ibis model reference designs ? cn0105 reference materials customer case studies ? analog devices retains domination in data converters product selection guide ? sar adc & driver quick-match guide technical articles ? ms-1779: nine often overlooked adc specifications ? ms-2210: designing power supplies for high speed adc tutorials ? mt-001: taking the mystery out of the infamous formula, "snr=6.02n + 1.76db", and why you should care ? mt-002: what the nyquist criterion means to your sampled data system design ? mt-031: grounding data converters and solving the mystery of "agnd" and "dgnd" ? mt-074: differential drivers for precision adcs design resources ? ad7626 material declaration ? pcn-pdn information ? quality and reliability ? symbols and footprints discussions view all ad7626 engineerzone discussions. sample and buy visit the product page to see pricing options. technical support submit a technical question or find your regional support number. document feedback submit feedback for this data sheet. this page is dynamically generated by analog devices, inc., and inserted into this data sheet. a dynamic change to the content on this page will not trigger a change to either the revision number or the content of the product data sheet. this dynamic page may be frequently modified.
ad7626 data sheet rev. d | page 2 of 29 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 functional block diagram .............................................................. 1 general description ......................................................................... 1 revision h istory ............................................................................... 2 specifications ..................................................................................... 3 timing specifications .................................................................. 6 timing diagrams .......................................................................... 7 absolute maximum ratings ............................................................ 8 ther mal resistance ...................................................................... 8 esd caution .................................................................................. 8 pin configuration and function descriptions ............................. 9 typical performance characteristics ........................................... 11 terminology .................................................................................... 15 theory of operation ...................................................................... 16 circuit information .................................................................... 16 converter information .............................................................. 16 transf er functions ..................................................................... 17 analog inputs .............................................................................. 17 typical connection diagram ................................................... 18 driving the ad7626 ................................................................... 19 voltage reference options ........................................................ 21 power supply ............................................................................... 22 digital interface .......................................................................... 23 applications information .............................................................. 25 layo ut, decoupling, and grounding ....................................... 25 outline dimensions ....................................................................... 26 ordering guide .......................................................................... 26 revision history 4/16 rev. c to rev. d changes to internal reference parameter, table 2 ....................... 4 added acquisition time parameter, table 3 ................................ 6 change to table 5 ............................................................................. 8 change to figure 32 caption and figure 33 caption ................ 19 10 /15 rev. b to rev. c changes to table 1 ............................................................................ 1 added aperture delay parameter and current drain parameter, table 2 ............................................................................. 3 changes to ordering guide .......................................................... 26 7 /1 2 rev. a to rev. b changed cp - 32- 2 package to cp - 32- 7 package ............. universal changes to figure 4 ........................................................................... 8 updated outline dimensions ...................................................... 25 changes to ordering guide .......................................................... 25 1/10 rev. 0 to rev. a changes to description of pin 5 and pin 6, table 6 ..................... 8 changes to power - up section ...................................................... 21 9 /09 revision 0: initial version
data sheet ad7626 rev. d | page 3 of 29 specifications vdd1 = 5 v; vdd2 = 2.5 v; vio = 2.5 v; ref = 4.096 v; all specifications t min to t max , unless otherwise noted. table 2 . parameter test conditions /comments min typ max unit resolution 16 bits analog input voltage range v in+ ? v in? ? v ref + v ref v operating input voltage v in+ , v in? to agnd ? 0.1 v ref + 0.1 v common - mode input range v ref /2 ? 0.05 v ref /2 v ref /2 + 0.05 v cmrr f in = 1 mhz 6 8 db input current midscale input 168 a throughput complete cycle 1 00 ns throughput rate 0. 1 10 msps dc accuracy integral linearity error ? 1 .5 0.45 +1 .5 lsb no missing codes 16 bits differential linearity error ? 0.5 0.3 5 +0.5 lsb transition noise 0.6 lsb zero error, t min to t max ? 6 1 + 6 lsb zero error drift 0.5 p pm / c gain error, t min to t max 8 20 lsb gain error drift 0. 7 ppm /c power supply sensitivity 1 vdd1 = 5 v 5% 0.4 lsb vdd2 = 2.5 v 5% 0.2 lsb ac accuracy f in = 20 khz, ?0.5 dbfs dynamic range 90.5 91.5 db signal -to - noise ratio 90 91 db spurious - free dynamic range 105 db total harmonic distortion ? 105.5 db signal -to - (noise + distortion) 89.5 91 db f in = 100 khz, ? 0.5 dbfs signal -to - noise ratio 91.3 db spurious - free dynamic range 1 04.5 db total harmonic distortion ? 102.5 db signal -to - (noise + distortion) 91 db f in = 2.4 mhz, ?1 dbfs signal -to - noise ratio 88.5 dbfs spurious - free dynamic range 84 db total harmonic distortion ? 86 db signal -to - (noise + distortion) 85 db f in = 2.4 mhz, ?6 dbfs signal -to - noise ratio 89 dbfs spurious - free dynamic range 84 db total harmonic distortion ? 93 db signal -to - (noise + distortion) 88 db ? 3 db input bandwidth 95 mhz aperture delay 1.5 ns aperture jitter 0.25 ps rms
ad7626 data sheet rev. d | page 4 of 29 parameter test conditions /comments min typ max unit internal reference output voltage refin at 25c 1.1 4 1.1 8 1.2 2 v temperature drift ? 40c to +85c 15 ppm/c reference buffer refin input voltage range 1.18 1.2 1.22 v ref output voltage range ref at 25c, en0 = en1 = 1 4.076 4.096 4.116 v line regulation vdd1 5%, vdd2 5% 5 mv external reference voltage range ref 4.096 v current drain 10 msps 570 a vcm pin vcm output ref/2 vcm error ? 0.0 15 +0.015 v output impedance 5 k? lvds i/o (ansi -644) data format serial lvds twos complement differential output voltage, v od r l = 100 ? 245 290 454 mv c ommon - mode output voltage, v ocm r l = 100 ? 980 2 1130 1375 mv differential input voltage, v id 100 650 mv common - mode input voltage, v icm 800 1575 mv power supplies specified performance vdd1 4.75 5 5.25 v vdd2 2.37 2.5 2.63 v vio 2.37 2.5 2.63 v operating currents static not converting vdd1 3.5 4.5 ma vdd2 16.7 21.2 ma vio 11.6 13. 5 ma with internal reference 10 msps throughput vdd1 10.4 11.2 ma vdd2 23.5 27. 8 ma vio echoed clock mode 15.8 17. 8 ma with external reference 10 msps throughput vdd1 7.5 8 .8 ma vdd2 23 28 ma vio echoed clock mode 16.4 18.5 ma power - down en0 = 0, en1 = 0 vdd1 0.6 4 a vdd2 0.8 10 a vio 1 5 a power dissipation 3 static not converting 88 107 mw with internal reference 10 msps throughput 150 170 mw with external reference 10 msps throughput 136 160 mw power - down 8 58 w energy per conversion 10 msps throughput 13.6 nj/sample
data sheet ad7626 rev. d | page 5 of 29 parameter test conditions /comments min typ max unit temperature range specified performance t min to t max ? 40 +85 c 1 using an external reference. 2 the ansi - 644 lvds i/o specification has a minimum output common mode (v ocm ) of 1125 mv. 3 power dissipation is for the ad7626 device only. in self clocked interface mode, 0.9 mw is dissipated in the 100 ? terminator. in echoed clock interface mode, 1. 8 mw is dissipated in two 100 ? terminators.
ad7626 data sheet rev. d | page 6 of 29 timing specification s vdd1 = 5 v; vdd2 = 2.5 v; vio = 2.3 7 v to 2. 6 3 v; ref = 4.096 v; all specifications t min to t max , unless otherwise noted. table 3 . parameter symbol min typ max unit time b etween c onversion s 1 t cyc 100 10, 000 ns acquisition time t acq 40 ns cnv h igh time t cnvh 10 40 ns cnv to d (msb) ready t msb 1 00 ns cnv to l ast clk (lsb) d elay t clkl 7 2 ns clk p eriod 2 t clk 3.33 4 (t cyc ? t msb + t clkl )/n ns clk f requency f clk 250 3 00 mhz clk to dco delay ( e cho ed c lock m ode) t dco 0 4 7 ns dco to d delay ( echoed clock mode ) t d 0 1 ns clk to d delay t clkd 0 4 7 ns 1 the maximum time be tween conversions is 10,000 ns. if cnv is left idle for a time greater than the maximum value of t cyc , the subsequent conversion result is invalid. 2 for the maximum clk period, the window available to read data is t cyc ? t msb + t c lkl . divide this time by the number of bits (n) to be read giving the maximum clk frequency that can be used for a given conversion cnv frequency. in echoed clock interface mode, n = 16; in self clocked inte rface mode, n = 18.
data sheet ad7626 rev. d | page 7 of 29 timing diagrams clk+ t cyc 1615 cnv+ 11 6 15 2 123 t cnvh t clkl dco+ 1615 1 16 15 2 1 23 d+ sample n s a mple n + 1 d? d15 n d14 n d1 n clk? cnv? dco? d0 n ? 1 acquisition acquisition acquisition t dco t d t clk 0 t msb d1 n ? 1 d15 n + 1 d14 n + 1 d0 n 0 d13 n + 1 t clkd 0 7648-003 figure 2. echoed clock interface mode timing diagram clk+ 18 17 1 4 2 1 23 t clkl d+ d? clk? d0 n ? 1 d1 n ? 1 acquisition acquisition acquisition t clkd t clk t msb 18 17 3 d15 n d14 n d1 n 0 0 1 d0 n d15 n + 1 0 0 1 t cyc c nv+ t cnvh sample n s a mple n + 1 cnv? 07648-004 figure 3. self clocked interface mode timing diagram
ad7626 data sheet rev. d | page 8 of 29 absolute maximum rat ings table 4 . parameter rating analog inputs/outputs in+, in? to gnd 1 ? 0.3 v to ref + 0.3 v or 130 ma ref 2 to gnd ? 0.3 v to +6 v vcm, cap2 to gnd ? 0.3 v to +6 v cap1, refin to gnd ? 0.3 v to + 2.7 v supply voltage vdd1 ? 0.3 v to +6 v vdd2, vio ? 0.3 v to +3 v digital inputs to gnd ? 0.3 v to vio + 0.3 v digital outputs to gnd ? 0.3 v to vio + 0.3 v input current to any pin except supplies 3 10 ma operating temperature range (commercial) ? 40c to +85c storage temperature range ? 65c to +150c junction temperature 150c esd 1 kv 1 see the analog inputs section. 2 keep cnv low for any external ref voltage > 4.3 v applied to the ref pin . 3 transient currents of up to 1 00 ma do not cause scr latch - up . stresses at or above those listed under absolute maximum ratings may cause permanent damage to the product. this is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the opera tional section of this specification is not implied. operation beyond the maximum operating conditions for extended periods may affect product reliability. thermal resistance ja is specified for the worst case conditions, that is, a device soldered in a circuit board for surface - mount packages. table 5 . thermal resistance package type ja jc unit 32- lead lfcsp_ w q 40 4 c/w esd caution
data sheet ad7626 rev. d | page 9 of 29 pin configuration an d function descripti ons 07648-002 notes 1. connect the exposed pad to the ground plane of the pcb using multiple vias. vdd1 vdd2 cap1 refin en0 en1 vdd2 cnv? gnd in+ in? vcm vdd1 vdd1 vdd2 clk+ cnv+ d? d+ vio gnd dco? dco+ clk? ref gnd ref ref cap2 gnd cap2 cap2 1 2 3 4 5 6 7 8 24 23 22 21 20 19 18 17 9 10 11 12 13 14 15 16 32 31 30 29 28 27 26 25 ad7626 top view (not to scale) figure 4. pin configuration table 6 . pin function descriptions pin no. mnemonic type 1 description 1 vdd1 p analog 5 v s upply . d ecouple the 5 v supply with a 100 nf capacitor . 2 vdd2 p analog 2.5 v s upply . decouple this pin with a 100 nf capacitor. the 2.5 v supply s ource s hould supply this pin first, then be traced to the other vdd2 pins (pin 7 and pin 18) . 3 cap 1 ao connect t his p in t o a 10 nf c apacitor. 4 refin ai/o preb uffer reference voltage . when using the internal reference, this pin outputs the band gap voltage and is nominally at 1.2 v. it can be overdriven with an external reference voltage such as the adr280 . in either internal or ext ernal reference mode, a 10 f capacitor is required. if using an external 4.096 v reference (connected to ref), this pin is a no connect and does not require any capacitor. 5, 6 en0, en1 di enable. operates from 2.5 v logic. the logic levels of these pins set the operation of the device as follows: en1 = 0, en0 = 0: power - down mode. en1 = 0, en0 = 1: external 1.2 v reference applied to the refin pin required. en1 = 1, en0 = 0: external 4.096 v reference applied to the ref pin required. en1 = 1, en0 = 1: internal reference and internal reference buffer in use. 7 vdd2 p digital 2.5 v s upply. decouple this pin with a 100 nf capacitor. 8, 9 cnv ? , cnv+ di convert input. th ese pin s act as the conversion control pin. on the rising edge of these pins, the analog input s are sampled and a conversion cycle is initiated . cnv+ works as a cmos input when cnv ? is grounded ; otherwise , cnv+ and cnv? are differential lvds inputs. 10, 11 d? , d+ do lvds data outputs. the conversion data is output serially on these pins. 12 vio p input/output interface s upply. use a 2.5 v supply and decouple this pin with a 100 nf capacitor. 13 gnd p ground. return path for the 100 nf capacitor connected to pin 12. 14, 15 dco?, dco+ do lvds buffered clock outputs. when dco+ is grounded, the self clock ed interface mode is sele cted. in this mode, the 16 - bit results on d are preceded by an initial 0 ( which is output at the end of the previous conversion ) , followed by a 2 - bit header (10) to allow synchronization of the data by t he digital host with extra logic. the 1 in this header provides the reference to acquire the subsequent conversion result correctly . when dco+ is not grounded, the echo ed clock interface mode is selected . in this mode, dco is a copy of clk . t he data bits are output on the falling edge of dco + and can be captured in the digital host on the next rising edge of dco + . 16, 17 clk ? , clk+ di lvds clock inputs. this clock shifts out the conversion results on the falling edge of clk+ . 18 vdd2 p analog 2.5 v supp ly. decouple this pin with a 100 nf capacitor. 19 , 20 vdd1 p analog 5 v s upply. isolate th ese pin s from pin 1 with a ferrite bead and decouple them with a 100 nf capacitor . 21 vcm ao common - mode output. when using any reference scheme, this pin produces one half the voltage present on the ref pin , which can be useful for driving the common mode of the input amplifiers. 22 in? ai differential negative analog input. referenced to and must be driven 180 out of phase with in+. 23 in+ ai differential positive analog input. referenced to and must be driven 180 out of phase with in ? . 24 gnd p ground.
ad7626 data sheet rev. d | page 10 of 29 pin no. mnemonic type 1 description 25, 26, 28 cap2 ao connect all three cap2 pins together and decouple them with the shortest trace possible to a single 10 f , low esr, low esl capacitor. the other side of the capacitor must be placed close to p in 2 7 (gnd). 27 gnd p ground. return path for the 10 f capacitor connected to p in 25, pin 26, and pin 28. 29, 30, 32 ref ai/o buffered reference voltage. when using the internal reference or the 1.2 v external reference (refin input), the 4.096 v system ref erence is produced at this pin. when using an external reference, such as the adr434 or the adr444 , the internal reference buffer must be disabled. in either case, connect all three ref pins together and decouple them with the shortest trace possible to a single 10 f , low esr, low esl capacitor. the other side of the capacitor must be placed close to p in 31 (gnd) . 31 gnd p ground. return path for the 10 f capacitor connected to pin 29, pin 30, and pin 32. ep exposed p ad the e xposed p ad is l ocated on the underside of the package. connect the exposed pad to the ground plane of the pcb using multiple vias. see the ex posed paddle section for more information . 1 ai = analog input; ai/o = bidirectional analog; ao = analog output; di = digital input; do = digital output; p = power.
data sheet ad7626 rev. d | page 11 of 29 typical performance characte ristics vdd1 = 5 v; vdd2 = 2.5 v; vio = 2.5 v; ref = 4.096 v; a ll plots at 10 msps unless otherwise noted. fft plots for 2 mhz, 3 mhz, and 5 mhz input tones use band pass filter ( 400 khz pass bandwidth around fundamental frequency). 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 30 10 50 70 90 amplitude (db) frequency (khz) input frequency = 10.37khz snr = 91.85db sinad = 91.8db thd = ?112.1db sfdr = 112.85db 32k samples 07648-108 figure 5. 10 khz, ?0.5 db input tone, zoomed view 0 ?20 ?40 ?60 fifth harmonic third harmonic second harmonic ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 amplitude (db) frequency (mhz) input frequency = 2.0026mhz ?0.5db input amplitude snr = 87.4dbfs sinad = 84.8dbfs thd = ?87.9db sfdr = 88.1db 64k samples 07648-402 figure 6. fft, 2 mhz, 0.5 db input tone, wide view 0 ?20 ?40 ?60 second harmonic third harmonic ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 amplitude (db) frequency (mhz) input frequency = 3.00125mhz ?0.5db input amplitude snr = 87.1dbfs sinad = 81.2dbfs thd = ?82.0db sfdr = 82.1db 64k samples 07648-404 fourth harmonic fifth harmonic figure 7. fft, 3 mhz, 0.5 db input tone, wide view 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 amplitude (db) frequency (mhz) 07648-118 input frequency = 100khz snr = 91.323db sinad = 91.047db thd = ?102.543db sfdr = 104.529db figure 8. 100 khz, 0.5 db input tone fft , full frequency view 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 fifth harmonic amplitude (db) frequency (mhz) input frequency = 2.0026mhz ?6db input amplitude snr = 87.6dbfs sinad = 87.6dbfs thd = ?101.6db sfdr = 101.9db 64k samples 07648-409 third harmonic second harmonic figure 9. fft, 2 mhz, 6 db input tone, wide view 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 amplitude (db) frequency (mhz) input frequency = 3.00125mhz ?6db input amplitude snr = 88.48dbfs sinad = 88.3dbfs thd = ?97.2db sfdr = 98.3db 64k samples 07648-411 third harmonic fourth harmonic second harmonic fifth harmonic figure 10 . fft, 3 mhz, 6 db input tone, wide view
ad7626 data sheet rev. d | page 12 of 29 0 ?20 ?40 ?60 second harmonic third harmonic ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 amplitude (db) frequency (mhz) input frequency = 5.00656128mhz ?0.5db input amplitude snr = 86.7dbfs sinad = 83.2dbfs thd = ?85.3db sfdr = 86.1db 64k samples 07648-406 fourth harmonic fifth harmonic figure 11 . fft, 5 mhz, ?0.5 db input tone, wide view 0 ?20 ?40 ?60 fundamental ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 amplitude (db) frequency (mhz) input frequency = 5.00656128mhz ?6db input amplitude snr = 88.4dbfs sinad = 88.0dbfs thd = ?92.4db sfdr = 92.8db 64k samples 07648-413 third harmonic fifth harmonic second harmonic fourth harmonic figure 12 . fft, 5 mhz, 6 db input tone, wide view ?75 ?80 ?85 ?90 ?95 ?100 ?105 ?110 ?115 ?18 0 ?15 ?12 ?9 ?6 ?3 thd (db) input amplitude (dbfs) 07648-211 1mhz 2mhz 3mhz 5mhz 9.7mhz figure 13 . thd vs . input amplitudes at input frequency tones of 10 khz to 9.7 mhz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 4.50 4.55 4.60 4.65 4.70 4.75 4.80 4.85 4.90 4.95 5.00 amplitude (db) frequency (mhz) input frequency = 5.00656128mhz ?0.5db input amplitude snr = 86.7dbfs sinad = 83.2dbfs thd = ?85.3db sfdr = 86.1db 64k samples 07648-412 fundamental third harmonic fifth harmonic figure 14 . fft, 5 mhz, 0.5 db input tone zoomed view 0 ?20 ?40 ?60 fundamental ?80 ?100 ?120 ?140 ?160 ?180 4.50 4.55 4.60 4.65 4.70 4.75 4.80 4.85 4.90 4.95 5.00 amplitude (db) frequency (mhz) input frequency = 5.00656128mhz ?6db input amplitude snr = 88.4dbfs sinad = 88.0dbfs thd = ?92.4db sfdr = 92.8db 64k samples 07648-407 third harmonic fifth harmonic figure 15 . fft, 5 mhz, 0.5 db input tone zoomed view snr thd ?50 ?60 ?70 ?80 ?90 ?100 ?110 10k 10m 100k 1m thd (db) input frequency (hz) 07648-401 94 92 90 88 86 84 82 80 snr (dbfs) figure 16 . thd and snr vs. input frequency (0.5 db input tone)
data sheet ad7626 rev. d | page 13 of 29 92.0 90.0 90.2 90.4 90.6 90.8 91.0 91.2 91.4 91.6 91.8 ?40 80 60 40 20 0 ?20 snr (db) temperature (c) 07648-212 external reference internal reference figure 17. snr vs. temperature (?0.5 db, 20 khz input tone) 0.35 ?0.10 ?0.05 0 0.05 0.10 0.15 0.20 0.25 0.30 ?6 ?4 ?2 0 2 4 6 input current (ma) input common-mode voltage (v) +input current ?input current 07648-121 figure 18. input current (in+, in?) vs. di?erential input voltage (10 msps) ? 103.0 ?107.0 ?106.5 ?106.0 ?105.5 ?105.0 ?104.5 ?104.0 ?103.5 ?40 80 60 40 20 0 ?20 thd (db) temperature (c) 07648-214 external reference internal reference figure 19. thd vs. temperature (?0.5 db, 20 khz input tone) 92.0 90.0 90.2 90.4 90.6 90.8 91.0 91.2 91.4 91.6 91.8 ?40 80 60 40 20 0 ?20 sinad (db) temperature (c) 07648-215 external reference internal reference figure 20. sinad vs. temperature (?0.5 db, 20 khz input tone) 0 7648-301 7 6 5 4 3 2 1 0 ?1 ?40 80 60 40 20 0 ?20 zero error and gain error (lsb) temperature (c) zero error gain error figure 21. zero error and gain error vs. temperature count code (hex) 0 54 30,651 201,320 30,073 46 0 0 50,000 100,000 150,000 200,000 250,000 fec7 fec8 fec9 feca fecb fecc fecd 262,144 samples std deviation = 0.4829 0 7648-022 figure 22. histogram of 262,144 conversions of a dc input at the code center (internal reference)
ad7626 data sheet rev. d | page 14 of 29 41 30,206 201,614 30,250 33 0 50,000 100,000 150,000 200,000 250,000 fec8 fec9 feca fecb fecc fecd fece count code (hex) 0 0 262,144 samples std deviation = 0.4814 07648-024 figure 23 . histogram of 262,144 conversions of a dc input at the code center (external reference) 2130 128,084 129,601 2329 0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 fec6 fec7 fec8 fec9 feca fecb count code (hex) 0 0 262,144 samples std deviation = 0.5329 07648-023 figure 24 . histogram of 262,144 conversions of a dc input at the code transition 0.30 ?0.30 ?0.25 ?0.20 ?0.15 ?0.10 ?0.05 0 0.05 0.10 0.15 0.20 0.25 0 16,384 32,768 49,152 65,536 dnl (lsb) code 07648-112 figure 25 . differential nonlinearity vs. code (25oc) 0.8 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 0 16,384 32,768 49,152 65,536 inl (lsb) code +85c +25c ?40c 07648-115 figure 26 . integral nonlinearity vs. code vs . temperature
data sheet ad7626 rev. d | page 15 of 29 terminology common - mode rejection ratio (cmrr) cmrr is defined as the ratio of the power in the adc output at full - scale frequency, f, to the power of a 100 mv p - p sine wave applied to the common - mode voltage of v in+ and v in? at frequency , f s . cmrr (db) = 10 log( pf / pf s ) where: pf is the power at frequency , f , in the adc output. pf s is the power at frequency , f s , in the adc output. differential nonlinearity (dnl) error in an ideal adc, code transitions are 1 lsb apart. differential nonlinearity is the maximum deviation from this ideal value. it is often specified in terms of resolution for which no missing codes are guaranteed. integral nonlinearity (inl) err or linearity error refers to the deviation of each individual code from a line drawn from negative full scale through positive full scale. the point used as negative full scale occurs ? lsb before the first code transition. positive full scale is defined a s a level 1? lsb beyond the last code tr ansition. the deviation is meas ured from the middle of each code to the true straight line. dynamic range dynamic range is the ratio of the rms value of the full scale to the rms noise measured for an input typically at ? 60 db. the value for dynamic range is expressed in decibels. effective number of bits (enob) enob is a measurement of the resolution with a sine wave input. it is related to sinad and is expressed in bits by enob = [( sinad db ? 1.76)/6.02] gain error the first transition (from 100 000 to 10 0 001) should occur at a level ? lsb above nominal negative full scale (?4.0959375 v for the 4.096 v range). the last transition (from 011 110 to 011 111) should occur for an analog voltage 1? lsb below the n ominal full scale (+4.0959375 v for the 4.096 v range). the gain error is the deviation of the difference between the actual level of the last transition and the actual level of the first transition from the difference between the ideal levels. gain error drift the ratio of the gain error change due to a temperature change of 1 c and the full - scale range (2 n ). it is expressed in parts per million. least significant bit (lsb) the least significant bit, or lsb, is the smallest increment that can be represented by a converter. for a fully differential input adc with n bits of resolution, the lsb expressed in volts is n inp-p v lsb 2 (v) = power supply rejection ratio (psrr) va riations in power supply affect the full - scale transition but not the linearity of the converter. psrr is the maximum change in the full - scale transition point due to a change in power supply voltage from the nominal value. reference voltage temperature co efficient the r eference voltage temperature coefficient is derived from the typical shift of output voltage at 25c on a sample of parts at the maximum and minimum reference output voltage (v ref ) measured at t min , t(25c), and t max . it is expressed in ppm/ c as 6 10 c 25 ( ( c ppm/ = ) t C t ( ) ( v ) min v C ) max v ) ( tcv min max ref ref ref ref v ref ( max ) = maximum v ref at t min , t(25c), or t max . v ref ( min ) = minimum v ref at t min , t(25c), or t max . v ref (25 c ) = v ref at 25c. t max = +85c. t min = ?40c. signal -to - noise ratio (snr) snr is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the nyquist frequency, excluding harmonics and dc. the value for snr is expressed in decibels. signal -to - (noise + distortion) ratio (sinad) sinad is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the nyquist frequency, including harmonics but excluding dc. the value for sinad is expressed in decibels. spurious - free dynamic range (sfdr) sfdr is t he difference, in decibels, between the rms amplitude of the input signa l and the peak spurious signal (including harmonics) . total harmonic distortion (thd) thd is the ratio of the rms sum of the first five harmonic components to the rms value of a full - scale input signal and is expressed in decibels. zero error zero error is the difference between the ideal midscale input voltage (0 v) and the actual voltage producing the midscale output code. zero error drift the ratio of the zero error change d ue to a temperature change of 1 c and the full - scale code range (2 n ). it is expressed in parts per million.
ad7626 data sheet rev. d | page 16 of 29 theory of operation sw+ comp sw? in+ ref ( 4 . 096 v) gnd lsb msb 32, 7 68c 16, 3 84c 4c 2c c c c o n t r o l l o g i c cnv+, cnv? in? 32,768c 16,384c 4c 2c c c lsb msb gnd gnd d + , d ? c l k + , c l k ? dc o + , dco ? lvds interface d a ta t ran s f er conversion control output code switches control 07648-030 figure 27 . adc simplified schematic circuit information the ad7626 is a 10 msps , high precision, powe r efficient, 16- bit adc that uses sar - based architecture to provide a performance of 91.5 db snr, 0.45 lsb inl, and 0.3 5 lsb dnl. the ad7626 is capable of converting 10 ,000,000 samples per second ( 10 msps ). the device typically consumes 1 36 mw of power . the ad7 626 offers the added functionality of a high performance on - chip reference and on - chip reference buffer. the ad7626 is specified for use with 5 v and 2.5 v supplies (vdd1, vdd2). the interface from the digital host to the ad7626 uses 2.5 v logic only. the ad7626 uses an lvds interface to transfer dat a conversions. the cnv + and cnv? input s to the device activate the conversion of the analog input. the cnv+ and cnv? pin s can be applied using a cmos or lvds source. the ad7626 is housed in a spac e - saving, 32- lead, 5 mm 5 mm lfcsp. converter informatio n the ad7626 is a 10 msps adc that uses sar - based architecture to incorporat e a charge redistribution dac. figure 27 shows a simplified schematic of the adc. the capacitive dac consists of two identical arrays of 16 binary weighted capacitors that are connected to the two comparator inputs. during the a cquisition phase, t he t erminals of the array tied to the input of the comparator are connected to gnd via sw+ and sw?. all independent switches are connected to the analog inputs. in this way, the capacitor arrays are used as sampling capacitors and acquir e the analog signal on the in+ and in? inputs. a conversion phase is initiated when the acquisition phase is complete and the cnv input goes high. note that the ad7626 can receive a cmos or lvds f ormat cnv signal. when the conversion phase begins, sw+ and sw? are opened first. the two capacitor arrays are then disconnected from the inputs and connected to the gnd input. therefore, the differential voltage between the inputs (in+ and in?) captured at the end of the acquisition phase is applied to the comparator inputs, causing the comparator to become unbalanced. by switching each element of the capacitor array between gnd and 4.096 v (the reference voltage), the comparator input varies by binary we ighted voltage steps (v ref /2, v ref /4 v ref /65 , 536). the control logic toggles these switches, msb first, to bring the comparator back into a balanced condition. at the completion of this process, the control logic generates the adc output code. the ad7626 digital interface uses lvds to enable high data transfer rates. the ad7626 conversion result is available for reading after t msb (t ime from the conversion start until msb is available) has elapsed . the user must apply a burst lvds clk signal to the ad7626 to transfer data to the digital host. the clk signal outputs the adc conv ersion result onto the data output d. the bursting of the clk signal is illustrated in figure 41 and figure 42 and is characterized as follows: ? the differential voltage on clk should be held steady state in the time between t clkl and t m sb . ? the ad7626 has two data read modes. f or more information about the echoed clock and self clocked interface modes , see the digital interface section.
data sheet ad7626 rev. d | page 17 of 29 transfer functions the ad7626 uses a 4.096 v reference. the ad7626 converts the differential voltage of the antiphase analog inputs (in+ and in?) into a digital output. the analog inputs, in+ and in?, require a 2.048 v common-mode voltage (ref/2). the 16-bit conversion result is in msb first, twos complement format. the ideal transfer functions for the ad7626 are shown in figure 28 and table 7. 100 ... 000 100 ... 001 100 ... 010 011 ... 101 011 ... 110 011 ... 111 adc code (twos complement) analog input +fsr ? 1.5lsb +fsr ? 1lsb ?fsr + 1lsb ?fsr ?fsr + 0.5lsb 0 7648-031 figure 28. adc ideal transfer fu nctions (fsr = full-scale range) table 7. output codes and ideal input voltages description analog input (in+ ? in?) ref = 4.096 v digital output code twos complement (hex) fsr ? 1 lsb +4.095875v 0x7fff midscale + 1 lsb +125 v 0x0001 midscale 0 v 0x0000 midscale ? 1 lsb ?125 v 0xffff ?fsr + 1 lsb ?4.095875 v 0x8001 ?fsr ? 4.096 v 0x8000 analog inputs the analog inputs, in+ and in?, applied to the ad7626 must be 180 out of phase with each other. figure 29 shows an equivalent circuit of the input structure of the ad7626. the two diodes provide esd protection for the analog inputs, in+ and in?. care must be taken to ensure that the analog input signal does not exceed the reference voltage by more than 0.3 v. if the analog input signal exceeds this level, the diodes become forward-biased and start conducting current. these diodes can handle a forward-biased current of 130 ma maximum. however, if the supplies of the input buffer (for example, the supplies of the ada4899-1 in figure 33) are different from those of the reference, the analog input signal may eventually exceed the supply rails by more than 0.3 v. in such a case (for example, an input buffer with a short circuit), the current limitation can protect the device. 67 ? 25pf vdd1 cnv in+ or in? 0 7648-010 figure 29. equivalent analog input circuit the analog input structure allows the sampling of the true differential signal between in+ and in?. by using these differential inputs, signals common to both inputs are rejected. the ad7626 shows some degradation in thd with higher analog input frequencies. 45 50 55 60 65 70 75 1 10 100 1k 10k 100k 1m 10m input common-mode frequency (hz) cmrr (db) 0 7648-009 figure 30. analog input cmrr vs. frequency
ad7626 data sheet rev. d | page 18 of 29 typical connection diagram 07648-027 ad7626 c ref 10f 1, 2 v+ adr434 8 adr444 conversion 4 control cmos (cnv+ only) or lvds cnv+ and cnv? using 100 ? termination resistor digital interface signals digital host lvds transmit and receive vdd1 vdd2 cap1 refin en0 en1 vdd2 cnv? 24 23 22 21 20 19 18 cnv+ d? d+ vio gnd dco? dco+ clk? gnd in+ in? vcm vdd1 vdd1 vdd2 clk+ ref gnd ref ref cap2 gnd cap2 cap2 10nf 100nf 100nf 10 f adr280 8 vio 10k? 3 10k? control for enable pins vio (2.5v) 5 100? 100? paddle capacitor on output for stability 10f 1 100nf 100nf ferrite bead 6 vdd1 (5v) vdd2 (2.5v) vdd1 (5v) vdd2 (2.5v) 100nf vdd2 (2.5v) in+ in? vcm see the driving the ad7625 section 7 8 9 10 11 12 13 14 15 16 17 100? 100? 1 2 3 4 5 6 7 32 31 30 29 28 27 26 25 1 see the layout, decoupling, and grounding section. 2 c ref is usually a 10f ceramic capacitor with low esr and esl. 3 use pull-up or pull-down resistors to control en0 and en1 during power-up. en0 and en1 inputs can be fixed in hardware or controlled using a digital host (en0 = 0 and en1 = 0 puts the adc in power-down). 4 option to use a cmos (cnv+) or lvds (cnv) input to control conversions. 5 to enable self-clocked mode, tie dco+ to gnd. 6 connect pin 19 and pin 20 to vdd1 supply; isolate the trace to pin 19 and pin 20 from the trace to pin 1 using a ferrite bead similar to wurth 74279266. 7 see the driving the ad7626 section for details on amplifier configurations. 8 see the voltage reference options section for details. figure 31. typical application diagram
data sheet ad7626 rev. d | page 19 of 29 driving the ad7626 differential analog input source figure 33 shows an ada4899-1 driving each differential input to the ad7626. single-ended to differential driver for applications using unipolar analog signals, a single-ended to differential driver (as shown in figure 32) allows for a differential input into the device. this configuration, when provided with an input signal of 0 v to 4.096 v, produces a differential 4.096 v with midscale at 2.048 v. the one-pole filter using r = 20 and c = 56 pf provides a corner frequency of 140 mhz. the vcm output of the ad7626 can be buffered and then provide the required 2.048 v common-mode voltage. single-ended or fully differe ntial high frequency driver in applications that require higher input frequency tones, the ada4932-1 can drive the inputs to the ad7626 . the ada4932-1 is a differential driver, which also allows the user the option of single-ended to differential conversion. figure 34 shows the typical circuit for a 50 source impedance (ac-coupled in this example). the input to the ada4932-1 is configured to be balanced to the source impedance (in this case 50 ). further information on balancing the input impedance to the source impedance can be found on the ada4932-1 data sheet. the circuit shown in figure 34 operates with an overall gain of ~0.5 when the termination input termination is taken into account. alternatively, the ada4932-1 can be used with a fully differential sourceit acts as an inverting differential driver. 56pf 20? 20? 50? in+ in? ad7626 vcm v? v+ ad8031, ad8032 u2 u1 ada4899-1 ada4899-1 56pf 100nf 100nf 590? 590? analog input (unipolar 0v to 4.096v) 0 7648-033 figure 32. single-ended to di fferential driver circuit using ada4899-1 56pf 20 ? ?v s 0v to v ref +v s 56pf 20 ? ?v s v ref to 0v +v s c ref 10f 2 ref 1 ref gnd in+ in? ad7626 ada4899-1 1 see the voltage reference options section. connection to external reference signals is dependent on the en1 and en0 settings. 2 c ref is usually a 10f ceramic capacitor with low esl and esr. decouple ref and refin pins as per the en1 and en0 recommendations vcm ?v s +v s buffered vcm pin output gives the required 2.048v common-mode supply for analog inputs. vcm 2.048v ad8031, ad8032 ada4899-1 refin ref 1 c ref 10f 2 0.1f 07648-025 figure 33. driving the ad7626 from a differential analog source using ada4899-1
ad7626 data sheet rev. d | page 20 of 29 in+ in? ad7626 vcm 53.6? gnd 53.6? gnd 50? r35 499? 499? single-ended analog input ac-coupled 50? source 499? c 499? 20? 20? gnd 56pf c22 0.1f c24 0.1f gnd 56pf gnd 100nf ad8031 c15 0.1f gnd gnd ?2.5v +7.25v vdrv+ vcm 2 3 12 +in v ocm ?in pd fb? ?out +out fb+ 1 11 10 4 16 15 14 13 5 6 7 8 9 pad pad ?v s +v s ada4932-1 07648-130 figure 34 . high frequency input drive circuit using the ada4932 - 1; single - ended to differential configuration
data sheet ad7626 rev. d | page 21 of 29 voltage reference op tions the ad7626 allows flexible options for creating and buffering the reference voltage. the ad7626 conversions refer to 4.096 v only. the various options creating this 4.096 v reference are controlled by the en1 and en0 pins ( see table 8 ). table 8 . voltage reference options option en1 en0 reference mode a 1 1 power -u p . internal reference and internal reference buffer in use b 0 1 e xternal 1.2 v reference applied to refin pin required c 1 0 external 4.096 v r eference applied to ref pin required . 0 0 power - d own m ode ad7626 in+ in? ref refin 10f 10f decouple the ref and refin pins externally. en1 = 1 and en0 = 1 power-up?internal reference and reference buffer in use. no external reference circuitry required. a 07648-131 figure 35 . powered up , internal reference and internal reference buffer ad7626 in+ in? ref refin 10f 10f en1 = 0 and en0 = 1 external 1.2v reference connected to refin pin is required. b adr280 v? v out v+ 0.1f 0.1f 1.2v (2.4v v+ 5.5v) v+ connect 1.2v externa l reference t o refin pin. 1.2v refin input is buffered internal l y . it cre a tes a 4.096v reference for the adc. decouple the ref and refin pins external l y 07648-132 figure 36 . external 1.2 v reference using internal reference buffer ad7626 in+ in? ref refin en1 = 1 and en0 = 0 external 4.096v reference connected to ref pin is required. c connect buffered 4.096v signal to ref pin. decouple the ref pin externally. refin is a no connect. no connect 10f 10f adr434/ adr444 gnd v in v out 0.1f 0.1f (6.1v v in 18v) 4.096v vin ad8031 v+ 07648-133 figure 37 . external 4.096 v reference applied to ref pin
ad7626 data sheet rev. d | page 22 of 29 wake - up time from en1 = 0, en0 = 0 the ad7626 powers down when en1 and en0 are both set to 0 . selecting the correct refe rence choice from power - down, the user sets en1 and en0 to the required value shown in table 8 . the user may immediately apply cnv pulses to receive data conversion results. typical wake - up times for the selected reference settings are shown in table 9 . each time represents the duration from the en1, en0 logic transition to when the output of the adc is settled to 0.5 lsb accuracy. table 9 . wake - up time from en1 = 0, en0 = 0 reference mode en1 en0 wake - u p time (0.5 lsb accuracy) a power - up. internal reference and internal reference buffer in use 1 1 9.5 s ec b external 1.2 v reference applied to refin pin 0 1 25 ms c external 4.096 v reference applied to ref pin 1 0 65 s power supply the ad7626 uses both 5 v (vdd1) and 2.5 v (vdd2) power supplies, as well as a digital input/output interface supply (vio). vio allows a direct interface with 2.5 v logic only. vio and vdd2 can be taken from the same 2.5 v source; however, it is best practice to isolate the vio and vdd2 pins using separate traces as well as to decouple each pin separately. the 5 v and 2.5 v su pplies required for the ad7626 can be generated using analog devices, inc., ldos such as the adp3330 - 2.5 , adp3330 - 5 , adp3334 , and adp1708 . 50 55 60 65 70 75 80 85 90 1 10 100 1k 10k supply frequency (hz) psrr (db) internal reference used vdd2 vdd1 07648-011 figure 38 . psrr vs. supply frequency (350 mv p - p ripple on vdd2, 600 mv ripple on vdd1) power - u p when powering up the ad7626 device, first apply the 2.5 v vdd2 supply and vio voltage to the device. after the vio and 2.5 v vdd2 have been established, apply the 5 v vdd1 supply. if using an external reference with the ad7626 , ensure that the en0 and en1 pi ns are connected to the correct logic values associated with the reference option of choice and then apply the external reference voltage. finally, apply the analog inputs to the adc. 25 20 15 10 5 0 0 10 8 6 4 2 current (ma) throughput (msps) 07648-235 vdd1 external reference vdd1 internal reference vdd2 internal reference vdd2 external reference vio external reference vio internal reference figure 39 . current consumption vs . sampling r ate 160 140 120 100 80 60 40 20 0 0 10 9 8 7 6 5 4 3 2 1 power (mw) throughput (msps) 07648-236 internal reference external reference figure 40 . power d issipation vs. sampling rate
data sheet ad7626 rev. d | page 23 of 29 digital interface conversion control all analog-to-digital conversions are controlled by the cnv signal. this signal can be applied in the form of a cnv+/cnv? lvds signal, or it can be applied in the form of a 2.5 v cmos logic signal to the cnv+ pin. the conversion is initiated by the rising edge of the cnv signal. after the ad7626 is powered up, the first conversion result generated is invalid. subsequent conversion results are valid provided that the time between conversions does not exceed the maximum specification for t cyc . the two methods for acquiring the digital data output of the ad7626 via the lvds interface are described in the following sections. echoed clock interface mode the digital operation of the ad7626 in echoed clock interface mode is shown in figure 41. this interface mode, requiring only a shift register on the digital host, can be used with many digital hosts (such as fpga, shift register, and microprocessor). it requires three lvds pairs (d, clk, and dco) between each ad7626 and the digital host. the clock dco is a buffered copy of clk and is synchronous to the data, d, which is updated on the falling edge of dco + (t d ). by maintaining good propagation delay matching between d and dco through the board and the digital host, dco can latch d with a good timing margin for the shift register. conversions are initiated by a rising edge cnv pulse. the cnv pulse must be returned low ( t cnvh maximum) for valid operation. after a conversion begins, it continues until completion. additional cnv pulses are ignored during the conversion phase. after the time, t msb , elapses, the host should begin to burst the clk. note that t msb is the maximum time for the msb of the new conversion result and should be used as the gating device for clk. the echoed clock, dco, and the data, d, are driven in phase with d being updated on the falling edge of dco+; the host should use the rising edge of dco+ to capture d. the only requirement is that the 16 clk pulses finish before the time (t clkl ) elapses of the next conversion phase or the data is lost. from the t clkl to t msb , d and dco are driven to 0. set clk to idle low between clk bursts. clk+ t cyc 1615 cnv+ 11 6 15 2 123 t cnvh t clkl dco+ 1615 1 16 15 2 1 23 d+ sample n s a mple n + 1 d? d15 n d14 n d1 n clk? cnv? dco? d0 n ? 1 acquisition acquisition acquisition t dco t d t clk 0 t msb d1 n ? 1 d15 n + 1 d14 n + 1 d0 n 0 d13 n + 1 t clkd 0 7648-103 figure 41. echoed clock interface mode timing diagram
ad7626 data sheet rev. d | page 24 of 29 self clocked mode the digital operation of the ad7626 in self clocked interface mode is shown in figure 42. this interface mode reduces the number of traces between the adc and the digital host to two lvds pairs (clk and d) or to a single pair if sharing a common clk. multiple ad7626 devices can share a common clk signal. this can be useful in reducing the number of lvds connections to the digital host. when the self clocked interface mode is used, each adc data- word is preceded by a 010 sequence. the first zero is automatically on d once t msb has elapsed. the 2-bit header is then clocked out by the first two clk falling edges. this header synchronizes d of each conversion in the digital host because, in this mode, there is no data clock output synchronous to the data (d) to allow the digital host to acquire the data output. synchronization of the d data to the digital host acquisition clock is accomplished by using one state machine per ad7626 device. for example, using a state machine that runs at the same speed as clk incorporates three phases of this clock frequency (120o apart). each phase acquires the data d as output by the adc. the ad7626 data captured on each phase of the state machine clock is then compared. the location of the 1 in the header in each set of data acquired allows the user to choose the state machine clock phase that occurs during the data valid window of d. the self clocked mode data capture method allows the digital host to adapt the result capture timing to accommodate variations in propagation delay through any ad7626 , as, for example, where data is captured from multiple ad7626 s sharing a common input clock. conversions are initiated by a cnv pulse. the cnv pulse must be returned low (t cnvh maximum) for valid operation. after a conversion begins, it continues until completion. additional cnv pulses are ignored during the conversion phase. after the time, t msb , elapses, the host begins to burst the clk signal to the ad7626 . all 18 clk pulses are to be applied in the time window framed by t msb and the subsequent t clkl . the required 18 clk pulses must finish before t clkl (referenced to the next conversion phase) elapses. otherwise, the data is lost because it is overwritten by the next conversion result. set clk to idle high between bursts of 18 clk pulses. the header bit and conversion data of the next adc result are output on subsequent falling edges of clk during the next burst of the clk signal. clk+ 18 17 1 4 2 1 23 t clkl d+ d? clk? d0 n ? 1 d1 n ? 1 acquisition acquisition acquisition t clkd t clk t msb 18 17 3 d15 n d14 n d1 n 0 0 1 d0 n d15 n + 1 0 0 1 t cyc cnv+ t cnvh sample n s a mple n + 1 cnv? 07648-104 figure 42. self clocked interface mode timing diagram
data sheet ad7626 rev. d | page 25 of 29 applications informa tion layout, d ecoupling , and grounding when laying out the printed circuit board (pcb) for the ad7626 , follow the practices described in this section to obtain the maximum performance from the converter. ex posed paddle the ad7626 has an exposed paddle on the underside of the package. ? solder the paddle directly to the pcb. ? connect the paddle to the ground plane of the board using multiple vias , as shown in figure 43. ? decouple all supply pins except for pin 12 (vio) directly to the paddle, minimizing the current return path. ? pin 13 and pin 24 can be connected directly to the paddle. use vias t o ground at the point where these pins connect to the paddle. vdd1 supply routing and decoupling the vdd1 supply is connected to pin 1, pin 19, and pin 20. decouple t he supply using a 100 nf capacitor at pin 1. the user can connect this supply trace to pin 19 and pin 20 . use a series ferrite bead to connect the vdd1 supply from p in 1 to pin 19 and pin 20 . the ferrite bead isolate s any high frequency noise or ringing on the vdd1 supply. decouple the vdd1 supply to pin 19 and pin 20 using a 100 nf capacitor d ecoupled to ground at the exposed paddle. vio supply decoupling decouple the vio supply applied to p in 12 to ground at p in 13. layout and decoupling of p in 25 to pin 32 connect the output s of pin 25, pin 26, and pin 28 together and decouple them to p in 27 using a 10 f capacitor with low esr and low esl. reduce the inductance of the path connecting pin 25, pin 26, and pin 28 by widening the pcb traces connecting these pins. take a similar appr oach in the connections used for the referen c e pins of the ad7626 . connect pin 29, pin 30 , and pin 32 together using widened pcb traces to reduce inductance. in internal or external reference mode, a 4.096 v reference voltage is output on pin 29, pin 30, and pin 32 . decouple these pins to p in 31 using a 10 f capacitor with low esr and low esl . figure 43 shows an example of the recommended layout for th e under side of the ad7626 device. note the extended signal trace connecti ons and the outline of the capacitors decoupling the signals applied to the ref pins (pin 29, pin 30, and pin 32) and to the cap2 pins (pin 25 , pin 26 , and pin 28 ). 32 31 30 29 28 27 26 25 paddle 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 24 23 22 21 20 19 18 17 4.096v external reference (adr434 or adr444) 07648-013 figure 43 . pcb l ayout and decoupling r ecommendations for p in 24 to pin 32
ad7626 data sheet rev. d | page 26 of 29 outline dimensions compliant to jedec standards mo-220-whhd. 112408-a 1 0.50 bsc bot t om view top view pin 1 indic a t or 32 9 16 17 24 25 8 exposed pa d pin 1 indic a t or 3.25 3.10 sq 2.95 sea ting plane 0.05 max 0.02 nom 0.20 ref coplanarity 0.08 0.30 0.25 0.18 5.10 5.00 sq 4.90 0.80 0.75 0.70 for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. 0.50 0.40 0.30 0.25 min figure 44 . 32 - lead lead frame chip scale p ackage [lfcsp_w q] 5 mm 5 mm body, very very thin quad (cp - 32 - 7) dimensions shown in millimeters ordering guide model 1 , 2 temperature range package description package option 3 ad7626bcpz ? 40c to +85c 32- lead lead frame chip scale package [lfcsp_ w q] cp -32-7 ad7626bcpz -rl7 ? 40c to +85c 32- lead lead f rame chip scale package [lfcsp_w q] cp -32-7 eval - ad7626 fmcz evaluation board eval - sdp -c h 1z controller board 1 z = rohs compliant part. 2 the eval - sdp - ch1z board allows the pc to control and communicate with all analog devices evaluation boards with model numbers ending with the f mc designator. 3 formerly the cp - 32- 2 package.
data sheet ad7626 rev. d | page 27 of 29 notes
ad7626 data sheet rev. d | page 28 of 29 notes
data sheet ad7626 rev. d | page 29 of 29 notes ?2009C2016 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d07648-0-4/16(d)

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