Can any champs of video decoder help me to answer below questions? Thanks in advance.
1.The below circuit cut from tvp5158evm. The question is if I change the inverse resistor from 0 ohm to 37.4 ohm, the effect shall not have serious change. Is my suppose right? So, I want to know why use the 37.4 ohm.
2. As the above circuit, If I left open on VIN1-4 and AIN1-4, the external noise will interfere on those pins. Is my suppose right?
For example, if the noise voltage is higher than power IC, the result will generate two ductile problems.
Q1. Does this situation impact the other channels?
Q2. Does this situation make the IC latch-up phenomenon?
1. 37.4-ohms is recommended to match the Thevenin resistance of a 75-ohm video source impedance terminated with 75 ohms (75//75 = 37.5) . 0 ohms would be best if the inputs were driven by a buffer with low source impedance. An incorrect resistor could have some an impact on noise cancelation.
2-1. We sometimes tie unused analog inputs to ground, but this is not an absolute requriement with TVP5158. The analog video inputs have separate paths and should not be affected by unused inputs. Tying these pins to ground using a resistor could potentially reduce internal noise and power consumption, but this could also be accomplished by powering down unused channels using REG 1Ah. Installing a connection to ground using a resistor does provide a way to connect a signal to an input, in case it is needed for evaluation.
2-2. Floating the pins should not result in latch-up.
Thank you so much for your confirmation.
Another question want to consult with you. How do handle the unused pins like pin 16、17 and 19? Can you provide a internal circuit to explain the reason why that can leave open or connect a resistor to the ground? Thanks in advance.
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