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LM1203 データシート(PDF) 9 Page - National Semiconductor (TI) |
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LM1203 データシート(HTML) 9 Page - National Semiconductor (TI) |
9 / 16 page Circuit Description (Continued) The ‘‘Drive’’ pin will allow the user to trim the Q9 gain of each amplifier to correct for differences in the CRT and high voltage cathode driver gain stages A small capacitor (33 pF) at this pin will extend the high frequency gain of the video amplifier by compensating for some of the internal high frequency roll off To use this capacitor and still provide variable gain adjustment the 51X and series 100X pot should be used with the red and green drive pins The 91X resistor used with the blue drive pin will set the system gain to approximately 62 and allow adjustment of the red and green gains to 62 plus or minus 25% The video signal at the collector of Q9 is buffered and level shifted down by Q10 and Q11 to the base of the output emitter follower Q12 Between the emitter of Q12 and the video output pin is a 40X resistor which was included to prevent spurious oscilla- tions when driving capacitive loads An external emitter re- sistor must be added between the video output pin and ground The value of this resistor should not be less than 390X or package power limitations may be exceeded when worst case (high supply max supply current max temp) cal- culations are made If negative going pulse slewing is a problem because of high capacitive loads (l10 pF) a more efficient method of emitter pull down would be to connect a suitable resistor to a negative supply voltage This has the effect of a current source pull down when the minus supply voltage is b12V and the emitter current is approximately 10 mA The system gain will also increase slightly because less signal will be lost across the internal 40X resistor Pre- cautions must be taken to prevent the video output pin from going below ground because IC substrate currents may cause erratic operation The collector currents from the vid- eo output transistors are returned to the power supply at VCC 2 pin 23 When making power dissipation calculations note that the data sheet specifies only the VCC 1 supply current at 12V The IC power dissipation contribution of VCC 2 is dependent upon the video output emitter pull down load In applications that require video amplifier shut down be- cause of fault conditions detected by monitor protection cir- cuits pin 11 and the wiper arms of the contrast and bright- ness controls can be grounded without harming the IC This assumes some series resistance between the top of the control pots and VCC Figure 7 shows the internal construction of the pin 11 24V reference circuit which is used to provide temperature and supply voltage tracking compensation for the video amplifier inputs The value of the external DC biasing resistors should not be larger than 10 kX because minor differences in input bias currents to the individual video amplifiers may cause offsets in gain TLH9178 – 7 FIGURE 7 LM1203 Video Input Voltage Reference and Contrast Control Circuits http www nationalcom 9 |
同様の部品番号 - LM1203 |
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同様の説明 - LM1203 |
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