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LM1044 データシート(PDF) 6 Page - National Semiconductor (TI) |
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LM1044 データシート(HTML) 6 Page - National Semiconductor (TI) |
6 / 10 page Application Notes (Continued) Truth Table Control Logic EN C B A Channel Selected 22 19 20 21 1 0 0 0 CV1 RGB Outputs Muted 1 0 0 1 CV2 RGB Outputs Muted 1 0 1 0 CV3 RGB Outputs Muted 1 0 1 1 RGB1 with Sync1 1 1 1 1 RGB2 with Sync2 1 1 1 0 Mute 1 1 0 1 Mute 1 1 0 0 Mute 0 X X X Previous selection retained The shaded section of the truth table indicates selection compatible with the LM1038 four channel stereo audio switch logic to give a possible selection of CV1 a Audio1 CV2 a Audio2 CV3 a Audio3 RGB1 a Audio4 and RGB2 a Mute or Audio4 see Figure 3 The mute conditions in the table correspond to disabled CVSync (output pulled low) and high impedance RGB out- puts which may be connected in parallel with other device outputs for further expansion of the switch system If all the RGB inputs are being used to switch composite video sig- nals then the RGB outputs can be connected into the CV inputs to allow multiplexing down to 1 output from a large number of input signals LOGIC AND ENABLE INPUTS If undriven the enable input will assume a high impedance logic 1 condition and should be defined externally The Log- ic selection inputs have internal pulldowns typically 20 kX which will define logic low levels if unconnected giving CV1 in default of any other control input INPUT BIAS FOR CV CHANNELS The CV and Sync inputs are biased via internal 15 kX and 23 kX resistors respectively to the internally generated 7V bias (VS e 12V) level at pin 14 Input coupling capacitors need to be chosen to give an adequate low frequency re- sponse when driving the 15 kX input impedance for exam- ple for less than 2% tilt on a frame rate waveform 330 mF will be required Depending on the effectiveness of any fol- lowing clamp circuitry the input coupling capacitors may be reduced in value These inputs may also be driven with DC coupled signals provided the standing DC level is sufficient- ly near to 7V to maintain the output within the output signal range (45 to 85V for VS e 12V) The bias at pin 14 has a DC output resistance typically of 1 kX and requires a decoupling capacitor to properly define the gain and crosstalk To ensure an adequate low frequen- cy response this capacitor should be 100 mF or more This pin may also be biased from an external voltage source provided the output remains within the output window Note this bias will also affect the voltage at pin 13 INPUT BIAS FOR RGB CHANNELS The 6 RGB inputs may be biased in one of three ways 1) DC restored above an internal 45V level 2) Clamped to an internal 7V bias level 3) Driven directly with DC coupled signals With an AC coupled input signal and the clamp pulse held low the negative going peaks will DC restore to a level greater than 3 diode drops below the reference bias level at pin 13 typically 45V for VS e 12V The source resistance of the diode restoring path is 1 kX for currents below 200 mA Simplified Schematic of RGB Stage TLH9252 – 6 The simplified schematic of the CV stage is virtually identical to the RGB stage except that the CV stage does not incor- porate the clamp circuitry Clamping to the internal 7V bias is arranged by applying a positive going clamp pulse to pin 18 during a time when the input signals are at a black reference level This is usually during the back porch or during the blanking period of sig- nals without syncs The clamp pulse width should not be less than 3 ms During the time pin 18 is high all six inputs R1 R2 G1 G2 B1 and B2 are connected to the RGB bias voltage developed at pin 13 charging the input coupling capacitors to this level These coupling capacitors are cho- sen to optimize value versus tilt introduced during the active line period A value of 330 mF gives less than 1% tilt for input currents less than 20 mA The effective impedance of the clamp path when conducting is 300X The voltage at pin 13 is a low impedance 60X buffered version of the CV bias voltage at pin 14 and decoupling is required to remove high frequencies and maintain channel separation The voltage at pin 13 may be changed by driving pin 14 as described for CV bias 6 |
同様の部品番号 - LM1044 |
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同様の説明 - LM1044 |
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