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TDA8708 データシート(PDF) 5 Page - NXP Semiconductors |
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TDA8708 データシート(HTML) 5 Page - NXP Semiconductors |
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5 / 24 page  June 1994 5 Philips Semiconductors Product specification Video analog input interface TDA8708A FUNCTIONAL DESCRIPTION The TDA8708A provides a simple interface for decoding video signals. The TDA8708A operates in configuration mode 1 (see Fig.4) when the video signals are weak (i.e. when the gain of the AGC amplifier has not yet reached its optimum value). This enables a fast recovery of the synchronization pulses in the decoder circuit. When the pulses at the GATE A and GATE B inputs become distinct (GATE A and GATE B pulses are synchronization pulses occurring during the sync period and rear porch respectively) the TDA8708A automatically switches to configuration mode 2 (see Fig.5). When the TDA8708A is in configuration mode 1, the gain of the AGC amplifier will be roughly adjusted (sync level to a digital output level of 0 and the peak level to a digital output level of 255). In configuration mode 2 the digital output of the ADC is compared to internal digital reference levels. The resultant outputs control the charge or discharge current of a capacitor connected to the AGC pin. The voltage across this capacitor controls the gain of the video amplifier. This is the gain control loop. The sync level comparator is active during a positive-going pulse at the GATE A input. This means that the sync pulse of the composite video signal is used as an amplitude reference. The bottom of the sync pulse is adjusted to obtain a digital output of logic 0 at the converter output. As the black level is at digital level 64, the sync pulse will have a digital amplitude of 64 LSBs. The peak-white control loop is always active. If the video signal tends to exceed the digital code of 248, the gain will be limited to avoid any over-range of the converter. The use of nominal signals will prevent the output from exceeding a digital code of 213 and the peak-white control loop will be non-active. The clamp level control is accomplished by using the same techniques as used for the gain control. The black-level digital comparator is active during a positive-going pulse at the GATE B input. The clamp capacitor will be charged or discharged to adjust the digital output to code 64. LIMITING VALUES In accordance with the Absolute Maximum Rating System (IEC 134). THERMAL CHARACTERISTICS SYMBOL PARAMETER MIN. MAX. UNIT VCCA analog supply voltage −0.3 +7.0 V VCCD digital supply voltage −0.3 +7.0 V VCCO output supply voltage −0.3 +7.0 V ∆VCC supply voltage difference between VCCA and VCCD −1.0 +1.0 V supply voltage difference between VCCO and VCCD −1.0 +1.0 V supply voltage difference between VCCA and VCCO −1.0 +1.0 V VI input voltage −0.3 VCCA V IO output current 0 +10 mA Tstg storage temperature −55 +150 °C Tamb operating ambient temperature 0 +70 °C Tj junction temperature 0 +125 °C SYMBOL PARAMETER VALUE UNIT Rth j-a thermal resistance from junction to ambient in free air SOT117-1 55 K/W SOT136-1 70 K/W |
同様の部品番号 - TDA8708 |
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同様の説明 - TDA8708 |
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