JTAG Series resistors understanding

[Bjtpower]

Hello Guys,

I am working on the stress analysis of the Resistors.

Where in a case of the JTAG Connections.

there is an Series resistor of 22 ohm between Controller and connectors.

Now if we calculate the current flowing through the resistor is 0.149A (Almost 150mA) and power drop across resistor come across 0.5W.

How we can can work on the duty cycle because it is operating on the almost 12 mhz

Kindly Help

Regards,
MARX

 

[FvM]

Presume the resistors are intended to reduce signal reflections, they may also play a role if ESD protection diodes are present (don't know if). They are surely not intended as short circuit protection, in so far your current and power calculations are inappropriate. Don't think that the involved drivers are capable of continuously supplying 150 mA without damage.

 

[Bjtpower]

No.. For stress analyis we have to consider the voltage across the resistor and and the duty cycle.

I dont know much about the Duty cycle.

I know it is a Fast communications.

Want to understand the dissipation against Frequency of Operations.
Frequency of Controller is 12MHZ

 

[FvM]

No.. For stress analysis we have to consider the voltage across the resistor and and the duty cycle.

Not applicable in this case. JTAG is operated with high impedance load, voltage drop across series resistors occurs only during signal edge when charging line capacitance, or in an unwanted short circuit condition. As said, it's probably useless to design the resistors for short circuit.

 

[Bjtpower]

But there should be some calculations and power loss ocurred across it.
I am using 22.1 OHM Resistor with 3.3 Will be logic high level voltage.

Regards
Marx

 

[FvM]

By nature of a series resistor, it's only generating voltage drop if there's a load current. But there should be no load current in JTAG lines.