AN-8006

AN-8006 Capacitor Selection for the FMS6410B S-Video Filter December 2005 AN-8006 Capacitor Selection for the FMS6410B S-Video Filter Method The FMS6410B requires 0.1µF input coupling capacitors, but may be AC or DC coupled out. Finding video quality — i.e., low ESR, equivalent series resistance, low inductance, low leakage, and constant capacitance over a frequency range from 20Hz to 6MHz — 0.1µF capacitors presents no problem. Surface mount capacitors meeting these requirements are both inexpensive and plentiful. The FMS6410B, when AC coupled out, also requires four 220µF output coupling capacitors if all outputs are to be used. See Figure 1. However, some users may use values up to 1000µF to pass “TILT” specifications in the two-field test. In the past, when wideband signals such as video needed coupling capacitors in the hundreds of µF’s, tantalums were the only choice. This presents a problem. The FMS6410B was designed for lowcost applications. In the quantities needed, the cost of the tantalums is greater than the cost of the filter and the other associated components. There is a solution: modern, surface mount, aluminum electrolytic capacitors designed for use in high-frequency switching power supplies have all the necessary qualities. For a given capacitance and voltage rating these electrolytics are about the same size as the tantalums. They also have low equivalent series resistance, low inductance, and low leakage. Since they are intended for use as bypass capacitors in switching power supplies operating up to 1MHz, they have an adequate frequency response as video coupling capacitors. Several types from several manufacturers have been investigated. Some 220µF surface mount aluminum electrolytic capacitors from Cornell Dubilier, Elna, and United Chemi-Con were indistinguishable from highquality, high-cost tantalums, as can be seen by comparing Figures 2 and 4 with Figures 3 and 5. It should be pointed out that these are not the only suppliers of usable capacitors. Any physically small, surface mount, 220µF, 6V to 10V, aluminum electrolytic capacitor with ESR less than 1Ω at 6MHz and with less than 2% capacitance change from 20Hz to 6MHz is a candidate for use in FMS6410B circuits. Many capacitors meet these requirements. With the right capacitors, their cost is no barrier to using the FMS6410B. FMS6410B 0.1µF YIN 1 5th-Order Filter + 8 220µF 75Ω Video Cables YOUT 75Ω 6 220µF 75Ω 75Ω 5 220µF 75Ω 75Ω C* 2 5V 220µF 75Ω 75Ω 7 3 R* On-Channel Modulator, VCR, and TV Σ + 0.1µF CIN 4 5th-Order Filter CVOUT CVOUT COUT 0.1µF 1µF * C and R depend on the input impedance of load Figure 1. AC Coupled S-Video and Composite Video Line Driver for NTSC AN-8006 Rev. 1.0 1 www.fairchildsemi.com ©2005 Fairchild Semiconductor Corporation AN-8006 Capacitor Selection for the FMS6410B S-Video Filter 0 1 2 0 1 2 Amplitude (dB) 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 Amplitude (dB) 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 Frequency (MHz) Frequency (MHz) Figure 2. -3dB Response with Tantalum Capacitor Figure 3. -3dB Response with Aluminum Electrolytic Capacitor 0 -10 0 -10 Amplitude (dB) -30 -40 -50 -60 -70 -80 10 100 1k 10k 100k 1M 10M 100M Amplitude (dB) -20 -20 -30 -40 -50 -60 -70 -80 10 100 1k 10k 100k 1M 10M 100M Frequency (Hz) Frequency (Hz) Figure 4. Wideband Response with Tantalum Capacitor Figure 5. Wideband Response with Aluminum Electrolytic Capacitor www.fairchildsemi.com 2 AN-8006 Rev. 1.0 AN-8006 Capacitor Selection for the FMS6410B S-Video Filter TRADEMARKS The following are registered and unregistered trademarks Fairchild Semiconductor owns or is authorized to use and is not intended to be an exhaustive list of all such trademarks. ACEx™ FAST® ActiveArray™ FASTr™ Bottomless™ FPS™ Build it Now™ FRFET™ CoolFET™ GlobalOptoisolator™ CROSSVOLT™ GTO™ DOME™ HiSeC™ EcoSPARK™ I2C™ E2CMOS™ i-Lo™ EnSigna™ ImpliedDisconnect™ FACT™ IntelliMAX™ FACT Quiet Series™ Across the board. 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PRODUCT STATUS DEFINITIONS Definition of Terms Datasheet Identification Advance Information Product Status Formative or In Design Definition This datasheet contains the design specifications for product development. Specifications may change in any manner without notice. This datasheet contains preliminary data, and supplementary data will be published at a later date. Fairchild Semiconductor reserves the right to make changes at any time without notice in order to improve design. This datasheet contains final specifications. Fairchild Semiconductor reserves the right to make changes at any time without notice in order to improve design. Preliminary First Production No Identification Needed Full Production Obsolete Not In Production This datasheet contains specifications on a product that has been discontinued by Fairchild semiconductor. The datasheet is printed for reference information only. Rev. I16 AN-8006 Rev. 1.0 3 www.fairchildsemi.com