Electronic Components Datasheet Search |
|
AD9561JR-REEL Datasheet(PDF) 7 Page - Analog Devices |
|
AD9561JR-REEL Datasheet(HTML) 7 Page - Analog Devices |
7 / 8 page AD9561 –7– REV. 0 Grounding and Bypassing Because the AD9561 uses analog circuits to achieve its superb gray scale resolution, caution must be exercised when incorpo- rating it into the mostly digital controller card for a printer. Achieving the accuracy designed into the AD9561 requires that interference due to improper grounding, power supply noise and digital coupling be minimized by following good layout practices. It is strongly urged that all following recommendations be followed. Factory characterization proves that a single ground plane dedicated to the AD9561 is most effective. This is atypical of many mixed signal circuits that use separate analog and digital grounds. Due to the operating speed of the AD9561, separate grounds result in erratic performance, which is eliminated by using a single isolated ground plane. This is because the DATA “low” value can be different from the ground value of the AD9561. All pins on the AD9561 labeled GROUND should be connected to the single dedicated ground plane. For best results, it is suggested that this plane be in the first interior layer under the IC. To assure logic level compatibility from the drive circuits to the AD9561, a single connection to the board’s main ground is necessary. The connection between the dedicated ground plane and the board’s main ground should be parallel to the path of the digital signals interfacing to the AD9561. High frequency return current seeks the path most parallel to the signal current. Whenever a parallel path does not exist, ground bounce results. CLOCK, DATA and CONTROL signal traces should run from the drive logic to the AD9561 in a group parallel to the connection between the system ground and the AD9561 ground. Using more than one signal plane will permit these traces to be as close to the ground interconnection as possible. This results in lowest impedance ground return and minimum ground interference due to digital switching. Attention to subtle layout characteristics can yield significant improvement in performance of high speed mixed signal ICs. The AD9561 pinouts were chosen for maximum isolation of sensitive pins such as RSET. The Pin 1 end of the IC should be oriented toward the source of the high speed digital inputs. This will help assure that these signal runs are short, with essentially the same length, thus having equal propagation delays. Most importantly, it will facilitate orienting traces to minimize coupling. High speed digital traces including DATA, CLOCK, SEM/ DEM, LEM/TEM and the OUTPUT should not pass under the body of the IC. The CLOCK, in particular, should enter perpendicular to the IC. For best results, the OUTPUT trace should exit perpendicular to the IC and pass through a via to a signal layer under the ground plane. This trace or any resistor or other component of the output circuit should not be parallel to RSET as electro- magnetic coupling can occur, causing the ramp current reference to be noisy and linearity to deteriorate. Optimally, RSET should be a chip resistor located on the same side of the board as the AD9561. It should be located close to Pin 14, without being close to the other IC pins. RSET should be on the top of the board with the AD9561 with no vias to add stray reactance and additional coupling paths. To reiterate the key layout considerations, high speed digital traces should not be located near the RSET pin or under the center of the IC body. A final interface consideration relates to rise/fall time of the high speed signals. Some logic families have rise and fall times as fast as 2 V/ns. This can result in on-chip parasitic coupling of these signals into the analog section. The undesirable effect can be eliminated by inserting series resistors in the DATA, SEM/DEM and LEM/ TEM connections. These resistors, in conjunction with the capacitance of the input pin and bond pad, will form a low pass filter to limit slew rate of the signals. The value of these resistors should be chosen based on trading off slower rise and fall time to possible interference to set up and hold times for faster clock rates. Power supply noise can also disrupt the linear circuits of the AD9561. Since switching power supplies are becoming the norm in most systems, caution should be exercised to minimize switching noise reaching the AD9561. The IC is designed for maximum power supply rejection. However, frequency content of switching supply noise often exceeds the frequency range of highest rejection. The preferred method would be to use a linear regulator from a higher supply voltage. If this is not practical, insert a ferrite bead in series with the supply connection. If possible, a VDD plane or a substantial width trace should connect VDD to Pin 7 first and then connect to each of the other VDD pins with wide traces. Thorough decoupling will complete a low pass filter for the supply. All VDD connections should be connected together. 0.1 µF chip capacitors should be connected as closely as possible to each VDD pin to the dedicated ground plane. Laboratory results indicate that performance is maximized when these chip capacitors are mounted on the same side of the PC card as the AD9561. If mounting chip components on the same side as the AD9561 is not a preferred manufacturing method, due consideration is encouraged to make an excep- tion, at least in the case of RSET and as many decoupling capacitors as practical. Additionally, a 10 µF tantalum capacitor should decouple the supply on the AD9561 side of the regulator or ferrite bead, also to the dedicated ground plane. For a recommended layout, see the AD9561/PCB data sheet. A copy can be obtained by calling Applications Support at 1-800-ANALOGD. |
Similar Part No. - AD9561JR-REEL |
|
Similar Description - AD9561JR-REEL |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |