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MC141627 bảng dữ liệu(PDF) 9 Page - Motorola, Inc |
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MC141627 bảng dữ liệu(HTML) 9 Page - Motorola, Inc |
9 / 16 page MC141627 9 MOTOROLA APPLICATION DESIGN CONSIDERATIONS VCC, GND To minimize noise effects for A/D, D/A, and all digital VCC and GND, wire up to the power supply separation. Leave the GND line as wide and short as possible. Furthermore, the wiring impedance should be as small as possible on the lay- out. To bypass noise, apply a high–capacity, high–perfor- mance frequency capacitor as close as possible to both analog and digital VCC and ground pins. A 0.1 µF multi–layer ceramic capacitor and a 47 µF tanta- lum capacitor are recommended. Vin In order to prevent flyback noise of the video input, it is necessary to keep the bandwidth to less than one half the clock frequency by using an area filter. Here the amplifier used as an input buffer needs a wide bandwidth and driving capability. Moreover, to minimize external noise effects, an input buffer should be driven by low impedance, and the Vin pin should be laid out as close as possible to the pattern lay- out. When using the built–in clamp circuit, connect CLout with Vin and input signals after ac coupling by using a high– performance capacitor. In this case, keep the Vin, CLout, cou- pling capacitor, and buffer–amplifier wiring as short as possible. Pay particular attention to external noise and para- sitic impedance. A/D Reference Pin The RTP and RBT pins provide a self–bias function that internally generates VTP = 2.5 V and VBT = 0.5 V. Presetting the A/D converter analog input dynamic range. A stable per- formance is achieved by installing high–performance, high– frequency capacitance as close as possible to the RTP and RBT pins and bypassing to GND(AD). A 0.1 µF multi–layer ceramic capacitor and a 10 µF tanta- lum capacitor are recommended. CLC The CLC pin sets the clamp circuit speed with an external capacitor and resistor. Generally, the capacitor and resistor are arranged in a row and connected with GND(AD). Select a capacitor that mini- mizes the dielectric absorbing error. When the capacitor capacity is reduced, the shift speed of the VCR signal to VCC(AD) side is accelerated. When the resistor value is reduced, the shift speed of the VCR signal to GND(AD) is ac- celerated. If the resistor value is too small at this point, sag- ging will appear in the VCR signal. Also, if the capacitor’s capacity is too large, the clamp speed will slow down; there- fore, it is very important to adjust the values of the resistor and capacitance to match the application. D/A Reference REF(DA) is a D/A converter reference decoupling pin for both the Yout and Cout. Bypass to GND(DA) by applying a high–performance frequency capacitor as close to the pin as possible. A 0.1 µF multi–ceramic capacitor is recommended. Clock Input The clock frequency inputs 3.58 MHz/4.43 MHz during nor- mal (FSC) mode, and 14.31818 MHz/17.734475 MHz during the other modes. The minimum input level is 1.0 V p–p. It should be phase–locked to the subcarrier of the video signal. The clock line should be wired with the shortest wire and be separated from other circuits to minimize cross coupling to other signals. The CLK(AD) pin is used only during digital input comb filtering mode; therefore, it should be in GND level except when the digital input comb filtering mode is se- lected. Ibias The Ibias pin is used to set up the bias current for the A/D and D/A converters. Connect an external resistor between the Ibias and GND(DA). Digital Input Comb Filtering Mode Connect CLK(AD) with the GND(D) when the A/D convert- er is not being used. Connect D0 – D7 with GND(D), when the D/A converter and filter are not being used. This is to eliminate any unnecessary operation of blocks which are not being used. At this point, make sure voltage is supplied to the VCC(AD), VCC(DA), and VCC(D). This eliminates latch–up during operating. Latch–Up The VCC(AD), VCC(DA), and VCC(D) pins are power supplies, independent from each other. Therefore, latch–up may occur when the power supply is turned on. To eliminate latch–up, turn on each power supply [VCC(AD), VCC(DA), and VCC(D) pins] simultaneously. |
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Mô tả tương tự - MC141627 |
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