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march 2007 rev 1 1/12 AN2471 application note stmav335 evaluation board & pcb layout recommendation introduction stmav335 has three sets of 3 to 1 switches that are well suited for switching analog video signals on the back panel of television sets or monitors. below is a diagram of an stmav335 typical application configuration: typical display unit back panel video input as illustrated above, stmav335 is used to swit ch one of the three vi deo input sets to the video receiver. depending on the sel inpu ts, ypbpr, rgb, or cvbs&s-video signals will be directed to the video receiver. hence less io is required at the video receiver to handle the many different video signal inputs on the display unit back panel. ultimately, integrating stmav3 35 to the system will result in a straightforward system design and overall cost reduction. ypbpr rgb cvbs&s - video ypbpr or r g b o r c v b s& s-v id eo stmav335 video receiver www.st.com
contents AN2471 2/12 contents 1 evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 video input & output ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 video input conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 pcb layout recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
AN2471 evaluation board 3/12 1 evaluation board the stmav335 evaluation board provides the customer with straightforward evaluation on the performance and the typical use of the switch in the real system. the boards include an stmav335 switch, video input and output connectors, jumper for setting the control lines status, and a power supply portion. 1.1 power supply the board can be powered either directly from a dc power supply or from a dc adaptor. if it is powered from a dc power supply, 5vdc is connected to the power socket labeled vcc5v and the ground is connected to the power socket labeled gnd. the board can also be powered from a dc adaptor having output voltage of 7 v to 15 v. the dc adaptor voltage will be regulated to 5 v by the on -board regulator. the dc adapt or can be center positive or negative and it should be connected to the dc jack. to prevent digital noise from coupling to the analog lines, the power distribution is separated from digital and analog sections. though stmav335 has also two digital lines, which are sel1 and sel2, it should still be powered from the analog supply . the reason is because its main function is to switch analog signals and those two digital lines are mostly static during operation. hence th e analog lines will not be disturbed by the digital part and as such, there is no need to have a separate analog and digital supply for stmav335. the analog and digital sections on the board are isolated by ferrite beads. note: external power can be applied to either vcc5v/gnd or dc jack, but not to both. table 1. power connector designator notes vcc5v connect to 5 v of external power supply. gnd connect to ground of external power supply. dc jack connect to dc adaptor output if the board is to be powered from dc adaptor. input voltage: 7 to 15 v
video input & output ports AN2471 4/12 2 video input & output ports stmav335 can switch three sets of video input to a single set of video output. on the evaluation board, the three sets of video input are: 1. rgb (vga port) 2. ypbpr (3 rca connector) 3. cvbs (rca connector) & s-video ( s-connector) in the real system, the outputs of stmav335 are directly connected to the video receiver. however for the stmav335 evaluation board, each output line branches to three signal lines. the reason for this is because each set of different video signal has a different type of connector. during evaluation, each output line should be branched and be connected to a different video connector on the display unit back panel by a cable. to avoid any pcb trace stub, the 1 to 3 branching of each output line cannot be shorted on the board. the branching of the output line is done by a zero ohm resistor. depending on which particular set of video signal is active, the zero ohm resistors should be soldered such that the output of stmav335 is connected to the right video output connector. note: sel1 jp9, sel2 jp10, open = '1' & close = '0' 2.1 video input conditioning the blanking level might vary between different video transmitters. this stmav335 evaluation board can handle video signals with blanking level of 0v to 2.5 v. if video signal blanking levels are outside the above range, some input conditioning should be done to modify the blanking level to the range specified. table 2. evaluation board video input & output input output sel 0 ? jumper output rgb (vga_in) rgb (vga_out) sel1 = ?1? sel2 = ?0? j11 = ?r? j12 = ?g? j13 = ?b? y (y_in) pb (pb_in) pr (pr_in) y (y_out) pb (pb_out) pr (pr_out) sel1 = ?0? sel2 = ?1? j11 = ?y? j12 = ?pb? j13 = ?pr? cvbs (cvbs_in) s-video (s video_in) cvbs (cvbs_out) s-video (s video_out) sel1 = ?0? sel2 = ?0? j11 = ?cvbs? j12 = ?y(s)? j13 = ?c?
AN2471 video input & output ports 5/12 figure 1. board schematic title number revision size a date: 4/17/2006 sheet of file: c:\documents and settings\..\stmav335.sc hdoc drawn by: sel1 1 y1 2 y2 3 r 4 pb1 5 pb2 6 g 7 pr/b 8 b 9 pr2 10 pr1 11 gnd 12 pb/g 13 y/r 14 sel2 15 vcc 16 u1 stmav335 red_in 1 green_in 2 blue_in 3 id_2 4 gnd 5 red_rtn 6 green_rtn 7 blue_rtn 8 nc 9 sync_rtn 10 id0 11 id1 12 h_sync 13 v_sync 14 id3 15 vga_in vga_con id2 id0 id1 h_sync v_sync id3 agnd r g b 2 1 y_in rca pb_in rca agnd agnd y pb vcc5v gnd 10uf c1 100nf c2 vcc5v 100pf c3 jp9 jp10 10k r1 10k r2 vcc5v_a sel1 sel2 agnd vcc5v_a agnd vcc5v_a red_out 1 green_out 2 blue_out 3 id_2 4 gnd 5 red_rtn 6 green_rtn 7 blue_rtn 8 nc 9 sync_rtn 10 id0 11 id1 12 h_sync 13 v_sync 14 id3 15 vga_out vga_con id2 id0 id1 h_sync v_sync id3 agnd l1 agnd vcc 1 gnd 2 gnd 3 dc jack dc plug + 1 - 2 ~ 3 ~ 4 u4 bridge rect gnd 1 vout 2 vin 3 u5 ld1117v50 10uf c4 vcc5v l2 vcc5v vcc5v_a pr_in rca agnd pr cvbs_in rca agnd cvbs y gnd 1 c gnd 2 y 3 c 4 shld 5 s video_in 2 1 y_out rca agnd pb_out rca agnd pr_out rca agnd cvbs_out rca agnd y gnd 1 c gnd 2 y 3 c 4 shld 5 s video_out agnd agnd vcc5v_a r g b y pb pr cvbs y(s) c c sel1 sel2 cvbs/y/r_out y(s) y(s)/pb/g_out c/pr/b_out in 1 out1 2 out2 3 out3 4 jp11 1 to 3 jumper in 1 out1 2 out2 3 out3 4 jp12 1 to 3 jumper in 1 out1 2 out2 3 out3 4 jp13 1 to 3 jumper cvbs/y/r_out y(s)/pb/g_out c/pr/b_out r_out r_out g_out g_out b_out b_out y_out y_out pb_out pb_out pr_out pr_out cvbs_out cvbs_out y(s)_out y(s)_out c_out c_out
video input & output ports AN2471 6/12 table 3. bill of material no component designator package manufacturer 1 stmav335 u1 tssop16 stmicroelectronics 2 s-video con s video_in, s video_out 3 vga female con vga_in, vga_out 4 rca con y_in, pb_in, pr_in,cvbs_in, y_out, pb_out, pr_out, cvbs_out 5 ld1117v50 u5 to-220 stmicroelectronics 6 df04m rectifier u4 dfm general semi 7 dc jack dc jack 8 power socket vcc5v, gnd 8 power socket vcc5v, gnd 9 ferrite bead l1, l2 1206 10 100 nf cap c2,c3 0603 11 10 f electrolytic cap c1, c4 cap7.62 mm 12 jumper jp9, jp10 hdr 2x1 13 10 k ? resistor r1, r2 0603 14 0 ? resistor jp11, jp12, jp13 0603
AN2471 pcb layout recommendation 7/12 3 pcb layout recommendation for the purpose of maintaining 75 ? track for all the analog lines, a 4-layer structure is recommended. all the analog tracks are routed on the top and bottom layers of the board. the middle two layers are used for both analog and digital ground. the middle two layers are identical and separated into two sections, analog and digital grounds. they are separated by a slot area and are only connected at the top layer through ferrite bead. this ensures th e digital noise will not get coup led to the analog portion. all the analog tracks are referenced to the analog ground and all the digital tracks are referenced to the digital ground. in this evaluation board sel1&sel2, that in the actual system would come from the digital portion of the system, are included in the analog portion. since these two select digital lines will be mostly stat ic during operation, it will not cause any disruption to the analog portion. stmav335 supply is connected to vcc5v analog and gnd analog. to further guarantee the stability of stmav335 supply, a 100 nf capacitor is used to decouple the vcc pin and should be placed as close as possible to the pi n. the stability of the an alog supply lines is of significant importance since the bias level of stmav335 is referenced to it. any instability on the analog supply will affect the switch characteristics. each set of video signals, rgb, ypbpr, and yc (s-video) are routed with the same track length. this will guarantee mi nimum channel-to-channel delay that will lead to minimum display distortion. figure 2. recommended board stack-up for 75 ? impedance
pcb layout recommendation AN2471 8/12 figure 3. pcb top layer
AN2471 pcb layout recommendation 9/12 figure 4. pcb middle layer1&2
pcb layout recommendation AN2471 10/12 figure 5. pcb bottom layer
AN2471 revision history 11/12 4 revision history table 4. document revision history date revision changes 13-mar-2007 1 initial release
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