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16-bit, 6 msps, pulsar differential adc data sheet ad7625 rev. b 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 rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 ?2009C2015 analog devices, inc. all rights reserved. technical support www.analog.com features throughput: 6 msps snr: 93 db inl: 0.45 lsb typical, 1 lsb maximum dnl: 0.3 lsb typical, 0.5 lsb maximum power dissipation: 135 mw 32-lead lfcsp (5 mm 5 mm) sar architecture no latency/no pipeline delay 16-bit resolution with no missing codes zero error: 1.5 lsb differential input voltage: 4.096 v serial lvds interface self-clocked mode echoed-clock mode can use lvds or cmos for conversion control (cnv signal) reference options internal: 4.096 v external (1.2 v) buffered to 4.096 v external: 4.096 v applications high dynamic range telecommunications receivers digital imaging systems high speed data acquisition spectrum analysis test equipment functional block diagram ad7625 clock logic serial lvds in? in+ refin ref v cm sar 2 cnv+, cnv? vio d+, d? dco+, dco? clk+, clk? 1.2v band gap cap dac 0 7652-001 figure 1. general description the ad7625 is a 16-bit, 6 msps, charge redistribution successive approximation register (sar) based architecture analog-to-digital converter (adc). sar architecture allows unmatched perfor- mance both in noise (93 db snr) and in linearity (1 lsb). the ad7625 contains a high speed, 16-bit sampling adc, an internal conversion clock, and an internal buffered reference. on the cnv rising 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 lvds self-clocked or echoed-clock serial interface, reducing external hardware connections. the ad7625 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 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 18 ad7643 ad7641 ad7960 ad7982 ad7986 ad7984
ad7625* product page quick links last content update: 02/23/2017 comparable parts view a parametric search of comparable parts. evaluation kits ? ad7625 evaluation kit documentation data sheet ? ad7625: 16-bit, 6msps, pulsar differential adc data sheet user guides ? ug-745: evaluating the ad7625/ad7626 16-bit, 6 msps/ 10 msps pulsar differential adc reference designs ? cn0080 ? cn0307 reference materials technical articles ? ms-2210: designing power supplies for high speed adc design resources ? ad7625 material declaration ? pcn-pdn information ? quality and reliability ? symbols and footprints discussions view all ad7625 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.
ad7625 data sheet rev. b | page 2 of 24 table of contents features .............................................................................................. 1 ? applications ....................................................................................... 1 ? functional block diagram .............................................................. 1 ? general description ......................................................................... 1 ? revision history ............................................................................... 2 ? specifications ..................................................................................... 3 ? timing specifications .................................................................. 5 ? absolute maximum ratings ............................................................ 6 ? thermal resistance ...................................................................... 6 ? esd caution .................................................................................. 6 ? pin configuration and function descriptions ............................. 7 ? typical performance characteristics ............................................. 9 ? terminology .................................................................................... 12 ? theory of operation ...................................................................... 13 ? circuit information .................................................................... 13 ? converter information .............................................................. 13 ? transfer functions ..................................................................... 14 ? analog inputs ............................................................................. 14 ? typical connection diagram ................................................... 15 ? driving the ad7625 ... ................................................................ 16 ? voltage reference options ........................................................ 17 ? power supply ............................................................................... 18 ? digital interface .......................................................................... 19 ? applications information .............................................................. 21 ? layout, decoupling, and grounding ....................................... 21 ? outline dimensions ....................................................................... 22 ? ordering guide .......................................................................... 22 ? revision history 10/15rev. a to rev. b changes to table 1 ............................................................................ 1 added aperture delay parameter and current drain parameter, table 2 ................................................................................................ 3 changes to clk period parameter and endnote 2, table 3 ... 5 changes to figure 32 caption and ordering guide .................. 22 7/12rev. 0 to rev. a change to table 5 .............................................................................. 6 changes to figure 2 ........................................................................... 7 updated outline dimensions (changed cp-32-2 to cp-32-7) .... 22 changes to ordering guide .......................................................... 22 1/09revision 0: initial version
data sheet ad7625 rev. b | page 3 of 24 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 gnd ?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 common-mode rejection ratio f in = 1 mhz 60 db input current midscale input 77 a throughput complete cycle 166 ns throughput rate 0.1 6 msps dc accuracy integral linearity error ?1 0.45 +1 lsb no missing codes 16 bits differential linearity error ?0.5 0.3 +0.5 lsb transition noise 0.6 lsb zero error t min to t max ?4 1.5 +4 lsb zero error drift 0.5 ppm/c gain error t min to t max 8 20 lsb gain error drift 0.4 ppm/c power supply sensitivity 1 vdd1 = 5 v 5% 0.4 lsb vdd2 = 2.5 v 5% 0.2 lsb ac accuracy external reference f in = 20 khz dynamic range 92.5 93.2 db signal-to-noise ratio 92 93 db spurious-free dynamic range 106 db total harmonic distortion ?105.5 db signal-to-(noise + distortion) 91.5 92 db internal reference f in = 20 khz dynamic range 92.5 93.2 db signal-to-noise ratio 91.5 92.9 db spurious-free dynamic range 106 db total harmonic distortion ?105.5 db signal-to-(noise + distortion) 91 92.5 db ?3 db input bandwidth 100 mhz aperture delay 1.5 ns aperture jitter 0.25 ps rms internal reference output voltage refin @ 25c 1.2 v temperature drift ?40c to +85c 15 ppm/c reference buffer refin input voltage range 1.2 v ref output voltage range 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 6 msps 590 a
ad7625 data sheet rev. b | page 4 of 24 parameter test conditions/comments min typ max unit vcm pin @ 25c output voltage ref/2 v output impedance 4 5 6 k lvds i/o (ansi-644) data format serial lvds twos complement differential output voltage, v od r l = 100 200 350 454 mv common-mode output voltage, v ocm 2 r l = 100 850 1250 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 staticnot converting vdd1 4.5 7.8 ma vdd2 17 22.7 ma vio self-clocked mode and echoed- clock mode 11 13 ma with internal reference 6 msps throughput vdd1 11 15.4 ma vdd2 21.5 28.3 ma vio self-clocked mode and echoed- clock mode 13.5 16 ma without internal reference 6 msps throughput vdd1 9 12.1 ma vdd2 21 26 ma vio self-clocked mode and echoed- clock mode 13.5 16 ma power dissipation 3 staticnot converting 95 130 mw with internal reference 6 msps throughput 145 190 mw without internal reference 6 msps throughput 135 165 mw energy per conversion 6 msps throughput 22 nj/sample temperature range specified performance t min to t max ?40 +85 c 1 using an external reference. 2 the ansi-644 lvds specification has a minimum output common mode (v ocm ) of 1125 mv. 3 power dissipation is for the ad7625 device only. in self-clo cked interface mode, 9 mw is dissipated in the 100 terminator. in echoed-clock interface mode, 18 mw is dissipated in two 100 terminators.
data sheet ad7625 rev. b | page 5 of 24 timing specifications vdd1 = 5 v; vdd2 = 2.5 v; vio = 2.37 v to 2.63 v; ref = 4.096 v; all specifications t min to t max , unless otherwise noted. table 3. parameter symbol min typ max unit time between conversions 1 t cyc 166 10,000 ns acquisition time t acq 40 ns cnv high time t cnvh 10 40 ns cnv to d (msb) delay t msb 145 ns cnv to last clk (lsb) delay t clkl 110 ns clk period 2 t clk (t cyc ? t msb + t clkl )/n 4 3.33 ns clk frequency f clk 250 300 mhz clk to dco delay (echoed-clock mode) 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 between 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 minimum clk period, the wind ow available to read data is t cyc ? t msb + t clkl . divide this time by the number of bits (n) that are read. in echoed-clock interface mode, n = 16; in self-clocked interface mode, n = 18.
ad7625 data sheet rev. b | page 6 of 24 absolute maximum ratings 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+/cnv? low for any external ref voltage > 4.3 v applied to the ref pin. 3 transient currents of up to 100 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 operational 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_wq 40 4 c/w esd caution
data sheet ad7625 rev. b | page 7 of 24 pin configuration and fu nction descriptions 07652-002 notes 1. connect the exposed pad to the ground plane of the pcb using multiple vias. ad7625 top view (not to scale) 1 gnd 2 in+ 3 in? 4 vcm 5 vdd1 6 vdd1 7 vdd2 8clk+ 24 23 22 21 20 19 18 17 vdd1 vdd2 cap1 refin en0 en1 vdd2 cnv? 9 10 11 12 13 14 15 16 cnv+ d? d+ vio gnd dco? dco+ clk? 32 31 30 29 28 27 26 25 ref gnd ref ref cap2 gnd cap2 cap2 figure 2. table 6. pin function descriptions pin no. mnemonic type 1 description 1 vdd1 p analog 5 v supply. decouple th e 5 v supply with a 100 nf capacitor. 2 vdd2 p analog 2.5 v supply. decouple this pin with a 100 nf capacitor. the 2.5 v supply source should supply this pin first and then be traced to the other vdd2 pins (pin 7 and pin 18). 3 cap1 ao connect this pin to a 10 nf capacitor. 4 refin ai/o prebuffer 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 external 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 pins. the logic levels of these pins set the operation of the device as follows: en1 = 0, en0 = 0: illegal state. en1 = 0, en0 = 1: enable internal buffer, disable internal reference. an external 1.2 v reference connected to the refin pin is required. en1 = 1, en0 = 0: disable internal reference and reference buffer. an external 4.096 v reference connected to the ref pin is required. en1 = 1, en0 = 1: enable internal reference and reference buffer. 7 vdd2 p digital 2.5 v supply. decouple this pin with a 100 nf capacitor. 8, 9 cnv?, cnv+ di convert input. these pins act as the conversion control pin. on the rising edge of these pins, the analog inputs are sampled and a conversion cycle is initiated. cnv+ works as a cmos input when cnv? is grounded; otherwise, cnv+ an d cnv? are differential lvds inputs. 10, 11 d?, d+ do lvds data outputs. the conver sion data is output se rially on these pins. 12 vio p input/output interface supply. 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-clocked interface mode is selected. in this mode, the 16-bit results on d are preceded by a 2-bit header (10) to allow synchronization of the data by the digital host with simple logic. when dco+ is not grounded, the echoed-clock inter- face mode is selected. in this mode, dco is a co py of clk. the data bits are output on the falling edge of dco+ and can be latched 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 supply. decouple this pin with a 100 nf capacitor. 19, 20 vdd1 p analog 5 v supply. isolate these pins from pin 1 with a ferrite bead and decoup le them with a 100 nf capacitor. 21 vcm ao common-mode output. when using any reference sc heme, 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.
ad7625 data sheet rev. b | page 8 of 24 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 th e capacitor must be placed close to pin 27 (gnd). 27 gnd p ground. return path for the 10 f capacitor connected to pin 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 reference 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 ca pacitor must be placed close to pin 31 (gnd). 31 gnd p ground. return path for the 10 f capacitor connected to pin 29, pin 30, and pin 32. ep exposed pad the exposed pad is located on the underside of the package. connect the exposed pad to the ground plane of the pcb using multiple vias. see the exposed pad 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 ad7625 rev. b | page 9 of 24 typical performance characteristics 07652-005 frequency (mhz) amplitude (db) 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 figure 3. fft 2 khz input tone, full view 07652-007 frequency (mhz) amplitude (db) 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 input tone = 50khz snr = 93.04db sinad = 92.63db thd = ?103.57db sfdr = ?102.69db figure 4. fft 50 khz input tone 0 16,384 32,768 49,152 65,536 ?0.4 ?0.3 ?0.2 ?0.1 0 0.1 0.2 0.3 0.4 0.5 ?0.5 07652-015 code dnl (lsb) figure 5. differential nonlinearity vs. code 07652-006 frequency (khz) amplitude (db) 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 5 10 15 20 25 30 35 40 45 input tone = 2khz snr = 93.16db sinad = 92.09db thd = ?110.45db sfdr = 111.37db figure 6. fft 2 khz input tone, zoom in on input tone and harmonics 07652-008 frequency (mhz) amplitude (db) 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 0 0.5 1.0 1.5 2.0 2.5 3.0 input tone = 100khz snr = 92.91db sinad = 92.55db thd = ?103.11db sfdr = ?103.41db figure 7. fft 100 khz input tone 0 16,384 32,768 49,152 65,536 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 0.8 1.0 ?1.0 07652-014 code inl (lsb) figure 8. integral nonlinearity vs. code
ad7625 data sheet rev. b | page 10 of 24 ?116 ?114 ?112 ?110 ?108 ?106 ?104 ?102 ?100 ?98 ?96 ? 94 0 20406080100120 07652-012 input frequency (khz) thd (db) ?0.5dbfs ?1dbfs ?3dbfs ?5dbfs ?10dbfs figure 9. thd at input am plitudes of ?0.5 dbfs to ?10 dbfs vs. frequency 92.2 92.4 92.6 92.8 93.0 93.2 93.4 93.6 93.8 ?60 ?40 ?20 0 20 40 60 80 100 120 07652-018 temperature (c) snr, dynamic range (db) dynr vs. temp internal ref dynr vs. temp external ref snr vs. temp internal ref snr vs. temp external ref figure 10. dynamic range and snr vs. temperature (?0.5 db, 20 khz input tone) ?60 ?40 ?20 0 20 40 60 80 100 120 ?4 ?6 ?20246 07652-010 differential input voltage (v) input current (a) in? in+ figure 11. input current (in+, in?) vs. differential input voltage (6 msps) ?103.5 ?103.0 ?102.5 ?102.0 ?101.5 ?101.0 ? 100.5 07652-021 thd (db) ?60 ?40 ?20 0 20 40 60 80 100 120 temperature (c) internal ref external ref figure 12. thd vs. temperature (?0.5 db, 20 khz input tone) 91.6 91.8 92.0 92.2 92.4 92.6 92.8 93.0 93.2 07652-019 sinad (db) ?60 ?40 ?20 0 20 40 60 80 100 120 temperature (c) sinad vs. temp internal ref sinad vs. temp external ref figure 13. sinad vs. temperature (?0.5 db, 20 khz input tone) 0 2 4 6 8 10 12 07652-020 zero error and gain error (lsb) ?60 ?40 ?20 0 20 40 60 80 100 120 temperature (c) gain error zero error figure 14. zero error and gain error vs. temperature
data sheet ad7625 rev. b | page 11 of 24 07652-022 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 figure 15. histogram of 262,144 conversions of a dc input at the code center (internal reference) 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 07652-024 count code (hex) 0 0 262,144 samples std deviation = 0.4814 figure 16. 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 07652-023 count code (hex) 00 262,144 samples std deviation = 0.5329 figure 17. histogram of 262,144 conversions of a dc input at the code transition (internal reference)
ad7625 data sheet rev. b | page 12 of 24 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 an 80 mv p-p sine wave applied to the common-mode voltage of v in+ and v in? at frequency f s . cmrr (db) = 10log( 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) error 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 as a level 1? lsb beyond the last code transition. 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 100 001) 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 nominal 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. 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 p-pin v lsb 2 (v) ? power supply rejection ratio (psrr) variations 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 coefficient the reference 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 ) meas- ured at t min , t(25c), and t max . it is expressed in ppm/c as 6 10 c25 ( ( cppm/ ? ?? ?? )tCt()(v )minvC)maxv )(tcv min max ref ref ref ref where: 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 (25c) = 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) (sinad) ratio 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 the difference, in decibels, between the rms amplitude of the input signal and the peak spurious signal. 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.
data sheet ad7625 rev. b | page 13 of 24 theory of operation 07652-030 sw+ comp sw? in+ ref (4.096v) gnd lsb msb 32,768c 16,384c 4c 2c c c control logic cnv+, cnv? in? 32,768c 16,384c 4c 2c c c lsb msb gnd gnd d+, d? clk+, clk? dco+, dco? lvds interface data transfer conversion control output code switches control figure 18. adc simplified schematic circuit information the ad7625 is a 6 msps, high precision, power efficient, 16-bit adc that uses sar based architecture to provide performance of 93 db snr, 0.45 lsb inl, and 0.3 lsb dnl. the ad7625 is capable of converting 6,000,000 samples per second (6 msps). the device typically consumes 135 mw. the ad7625 offers the added functionality of a high performance on-chip reference and on-chip reference buffer. the ad7625 is specified for use with 5 v and 2.5 v supplies (vdd1, vdd2). the interface from the digital host to the ad7625 uses 2.5 v logic only. the ad7625 uses an lvds interface to transfer data conversions. the cnv+ and cnv? inputs to the device activate the conversion of the analog input. the cnv+ and cnv? pins can be applied using a cmos or lvds source. the ad7625 is housed in a space-saving, 32-lead, 5 mm 5 mm lfcsp. converter information the ad7625 is a 6 msps adc that uses sar based architecture incorporating a charge redistribution dac. figure 18 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 acquisition phase, the terminals 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 acquire 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 logic high. note that the ad7625 can receive a cmos (cnv+) or lvds format (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 weighted 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 ad7625 digital interface uses low voltage differential signaling (lvds) to enable high data transfer rates. the ad7625 conversion result is available for reading after t msb (time from the conversion start until msb is available) has elapsed. the user must apply a burst lvds clk signal to the ad7625 to transfer data to the digital host. the clk signal outputs the adc conversion result onto the data output d. the bursting of the clk signal is illustrated in figure 29 and figure 30 and is characterized as follows: the differential voltage on clk should be held to create logic low in the time between t clkl and t msb . the ad7625 has two data read modes. for more information about the echoed-clock and self-clocked interface modes, see the digital interface section.
ad7625 data sheet rev. b | page 14 of 24 transfer functions the ad7625 uses a 4.096 v reference. the ad7625 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 ad7625 are shown in figure 19 and table 7. 07652-031 100 ... 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 figure 19. 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 +4.0959375 v 0x1fff midscale + 1 lsb +62.5 v 0x0001 midscale 0 v 0x0000 midscale ? 1 lsb ?62.5 v 0xffff ?fsr + 1 lsb ?4.0959375 v 0x1001 ?fsr ?4.096 v 0x1000 analog inputs the analog inputs, in+ and in?, applied to the ad7625 must be 180 out of phase with each other. figure 20 shows an equivalent circuit of the input structure of the ad7625 . 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 24) 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 be used to protect the device. 0 7652-032 in+ or in? cnv 25pf 250 ? v dd1 figure 20. equivalent analog input circuit the analog input structure allows the sampling of the true differential signal between in+ and in?. by using these differ- ential inputs, signals common to both inputs are rejected. the ad7625 shows some degradation in thd with higher analog input frequencies. 40 45 50 55 60 65 70 75 80 85 1 10 100 1k 10k 100k 1m 10m 07652-009 input common-mode frequency (hz) cmrr (db) figure 21. analog input cmrr vs. frequency
data sheet ad7625 rev. b | page 15 of 24 typical connection diagram 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, en1 during power-up. en0 and en1 inputs can be fixed in hardware or controlled using a digital host (en0 = 0 and en1 = 0 is an illegal state). 4 option to use a cmos (cnv+) or lvds (cnv) input to control conversions. 5 to enable self-clocked mode, tie dco+ to gnd using a pull-down resistor. 6 connect pin 19 and pin 20 to vdd1 supply; isolate from pin 1 using a ferrite bead similar to wurth 74279266. 7 see the driving the ad7625 section for details on amplifier configurations. 8 see the voltage reference options section for details. ad7625 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 07652-027 figure 22. typical application diagram
ad7625 data sheet rev. b | page 16 of 24 driving the ad7625 differential analog input source figure 24 shows an ada4899-1 driving each differential input to the ad7625 . single-ended-to-differential driver for applications using unipolar analog signals, a single-ended- to-differential driver, as shown in figure 23, allows for a differ- ential 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 = 33 and c = 56 pf provides a corner frequency of 86 mhz. the vcm output of the ad7625 can be buffered and then used to provide the required 2.048 v common-mode voltage. 56pf 33 ? 33 ? 50? in+ in? ad7625 vcm v? v+ ad8031, ad8032 07652-033 u2 u1 ada4899-1 ada4899-1 56pf 100nf 100nf 590? 590? analog input (unipolar 0v to 4.096v) figure 23. single-ended-to- differential driver circuit 56pf 33? ?v s 0v to v ref +v s 56pf 33? ?v s v ref to 0v +v s c ref 10f 2 ref 1 ref gnd in+ in? ad7625 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. the ref and refin pins are decoupled regardless of en1 and en0 settings. 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 07652-025 0.1f figure 24. driving the ad7625 from a differential analog source
data sheet ad7625 rev. b | page 17 of 24 voltage reference options the ad7625 allows flexible options for creating and buffering the reference voltage. the ad7625 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 1 option en1 en0 reference mode a 1 1 use internal reference and internal reference buffer (both are enabled). b 0 1 use external 1.2 v reference with internal reference buffer enabled. the internal reference is disabled. c 1 0 use external 4.096 v reference with an external reference buffer. the internal reference and reference buffer are disabled. 1 en1 = 0 and en0 = 0 is an illegal state. 10f adr434 adr444 ref in+ ad7625 v+ refin 10f adr280 v+ v? v+ setting en1 = 1 and en0 = 0 disables the internal reference and reference buffer. connect the buffered 4.096v signal to the ref pin. setting en1 = 1 and en0 = 1 enables the internal reference and reference buffer. decouple the ref and refin pins externally. in? b c a 0 7652-026 setting en1 = 0 and en0 = 1 disables the internal reference and enables the internal reference buffer. connect a 1.2v reference to the refin pin. the 1.2v applied to the refin pin is buffered internally to create a 4.096v reference for the adc. figure 25. voltage reference options
ad7625 data sheet rev. b | page 18 of 24 power supply the ad7625 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 and also to decouple each pin separately. the 5 v and 2.5 v supplies required for the ad7625 can be generated using analog devices, inc., low dropout regulators (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 vdd2 vdd1 07652-011 supply frequency (hz) psrr (db) internal reference used figure 26. psrr vs. supply frequency (350 mv pp ripple on vdd2, 600 mv ripple on vdd1) power-up when powering up the ad7625 device, first apply the vio voltage to the device so that the en1 and en0 values can be set for the reference option in use. connect the en0 and en1 pins to pull-up/pull-down resistors to ensure that one or both of these pins is set to a nonzero value. en0 = 0 and en1 = 0 is an illegal state that must be avoided. after vio is established, apply the 2.5 v vdd2 supply to the device followed by the 5 v vdd1 supply and then an external reference (depending on the reference setting being used). finally, apply the analog inputs to the adc. 07652-016 sampling rate (ksps) current (ma) 0 5 10 15 20 25 0 1000 2000 3000 4000 5000 6000 7000 vdd2 internal ref vdd2 external ref vdd1 external ref vdd1 internal ref vio figure 27. current consumption vs. sampling rate 07652-017 sampling rate (ksps) power dissipation (mw) 0 1000 2000 3000 4000 5000 6000 7000 60 70 80 90 100 110 120 130 140 150 internal ref external ref figure 28. power dissipati on vs. sampling rate
data sheet ad7625 rev. b | page 19 of 24 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 ad7625 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 ad7625 via the lvds interface are described in the following sections. echoed-clock interface mode the digital operation of the ad7625 in echoed-clock interface mode is shown in figure 29. this interface mode, requiring only a shift register on the digital host, can be used with many digital hosts (fpga, shift register, microprocessor, and so on). it requires three lvds pairs (d, clk, and dco) between each ad7625 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 be used to latch d with good timing margin for the shift register. 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. addi- tional 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 for the next conversion phase or the data is lost. from the time t clkl to t msb , d and dco are driven to 0s. 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 acq 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 7652-003 figure 29. echoed-clock interface mode timing diagram
ad7625 data sheet rev. b | page 20 of 24 self-clocked interface mode the digital operation of the ad7625 in self-clocked interface mode is shown in figure 30. this interface mode reduces the number of wires between adcs and the digital host to two lvds pairs per ad7625 (clk and d) or to a single pair if sharing a common clk using multiple ad7625 devices. self-clocked interface mode facilitates the design of boards that use multiple ad7625 devices. the digital host can adapt the interfacing scheme to account for differing propagation delays between each ad7625 device and the digital host. the self-clocked interface mode consists of preceding the results of each adc word with a 2-bit header on the data, d. this header is used to synchronize d of each conversion in the digital host. synchronization is accomplished by one simple state machine per ad7625 device. for example, if the state machine is running at the same speed as clk with three phases, the state machine measures when the logic 1 of the header occurs. 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. addi- tional 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 first bit of the header and should be used as the gating device for clk. clk is also used internally on the host to begin the internal synchronization state machine. the next header bit and conversion results are output on subsequent falling edges of clk. the only requirement is that the 18 clk pulses finish before the time t clkl elapses for the next conversion phase or the data is lost. set clk to idle high between bursts of 18 clk pulses. clk+ 1817 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? t acq 07652-004 figure 30. self-clocked interface mode timing diagram
data sheet ad7625 rev. b | page 21 of 24 applications information layout, decoupling, and grounding when laying out the printed circuit board (pcb) for the ad7625 , follow the practices described in this section to obtain the maxi- mum performance from the converter. exposed pad the ad7625 has an exposed pad on the underside of the package. ? solder the pad directly to the pcb. ? connect the pad to the ground plane of the board using multiple vias, as shown in figure 31. ? decouple all supply pins except for pin 12 (vio) directly to the pad, minimizing the current return path. ? pin 13 and pin 24 can be connected directly to the pad. use vias to ground at the point where these pins connect to the pad. vdd1 supply routing and decoupling the vdd1 supply is connected to pin 1, pin 19, and pin 20. the supply should be decoupled 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 pin 1 to pin 19 and pin 20. the ferrite bead isolates 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 to gnd. this gnd connection can be placed a short distance away from the exposed pad. vio supply decoupling decouple the vio supply applied to pin 12 to ground at pin 13. layout and decoupling of pin 25 to pin 32 connect the outputs of pin 25, pin 26, and pin 28 together and decouple them to pin 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. a similar approach should be taken in the connections used for the reference pins of the ad7625 . 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 pin 31 using a 10 f capacitor with low esr and low esl. figure 31 shows an example of the recommended layout for the underside of the ad7625 device. note the extended signal trace connections 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 12345678 9 10 11 12 13 14 15 16 24 23 22 21 20 19 18 17 4.096v external reference (adr434 or adr444) 07652-013 figure 31. pcb layout and decoupling recommendations for pin 24 to pin 32
ad7625 data sheet rev. b | page 22 of 24 outline dimensions compliant to jedec standards mo-220-whhd. 101515-a 1 0.50 bsc bottom view top view pin 1 indicator 32 9 16 17 24 25 8 exposed pad p i n 1 i n d i c a t o r 3.25 3.10 sq 2.95 s eating 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 32. 32-lead lead frame chip scale package [lfcsp_wq] 5 mm 5 mm body and 0.75 mm package height (cp-32-7) dimensions shown in millimeters ordering guide model 1, 2 temperature range package description package option ad7625bcpz ?40c to +85c 32-lead lead frame chip scale package [lfcsp_wq] cp-32-7 ad7625bcpzrl7 ?40c to +85c 32-lead lead frame chip scale package [lfcsp_wq] cp-32-7 eval-ad7625fmcz evaluation board EVAL-SDP-CH1Z 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 fm c designator.
data sheet ad7625 rev. b | page 23 of 24 notes
ad7625 data sheet rev. b | page 24 of 24 notes ?2009C2015 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d07652-0-10/15(b)

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