THVD8000: How about input impedance in receive mode? Does it need input bias network?

Hi John,

This device is 1/8th unit load - so we estimate the minimum input impedance at 12V input to be 96kohms (1 unit load is 12k - 1/8th Unit load is 8 times more resistive so 96k) - generally the input impedance is higher than 96k during operation. 

No bias circuitry is required to bring device up to known DC level - output is balanced with logic 0's being transmitted as a pulse train and logic 1's being transmitted as a 0V differential. 

For standard operation the only external components explicitly needed on the bus are the coupling network inductors and capacitors (below is a two node system example - more nodes can be used than 2 - but basically every node is going to be extremely similar):

Above is for a DC power system - for lower voltage AC power systems (<=36V) there is the need to add a filter capacitance across the main power supply to mitigate OOK signal from leaking to the power line. 

It is also generally a good idea to add a termination resistor between A and B pins of THVD8000 for both start and end node - usually 120 ohms - but this isn't as necessary in THVD80x0 applications because the cable is generally not impedance controlled - however it will help with some noise issues. 

For design reasons I highly encourage you and the end designer to read the following notes as the most common questions for designing with this device are answered there:

THVD8000 Design Guide: This goes over basic DC (<=50V) Power system implementations and walks through all the steps to design these DC systems

THVD80X0 Low Voltage AC (<=36VAC) Power System Application: Essentially modifications when using in an AC power system

High Voltage THVD80x0: If the power system is greater than 50V DC or 36V AC you may need to look at the high voltage implemenation (same for AC and DC systems)

Please let me know if you have any other questions and I will see what I can do!

Best,

Parker Dodson