Hi to all
I was looking the EZ-KIT schematic. About the dual supply for core and I/O(VDDINT, VDDEXT) thelast pin of Vddint31 is connected to Vcc trough a rezistor. Why is that? the sam is for VDDOI19?
Those resistors are zero ohm resistors and are provided in case you want to measure the current. Then you can remove them and measure the current. If you want to design your own custom board and have no plan to measure the current, you can remove the resistors and ties those pins directly to their correct voltages (VDDEXT or VDDINT).
Note: The correct answer is below by Greg. Please ignore this response.
thanks for answer.
I ve got another one question - where can i see how much is the currnet. Beacuse i want to use a buck regulator for example (LM3102) to provide 3.3V and 1.2V for the Vddext & Vddint but i don`t know how to choose it?
In order to find the power requirements for ADSP-21371 DSP you should look in:
EE-318 - Estimating Power Dissipation for ADSP-21371 SHARC® Processors
I read the EE-318 and i saw that the internal current is Iddint = 0.93A. and the external current Iddext = 0.062A. So the total currne is 0.062 + 0.93 = 0.992A? But in data sheet in table of the elecreical characteristics it`s written IDD-INTYP - 400mA or 600mA wich depence on Vddint. And in the EE 318 IDD EXT is 600mA , but in the datasheet this value is for IDD INT! Wich one i s the exact value?
Power consumption and DSP power calculation all depends on your applications. One application might use 5 times more current than another application. It also depends on the core CLOCK. You can not have a fix number number for current for all applications. So in order to design your power supply, you should consider the worst case in your case. As you said, the datasheet mentions the TYP (typical) current and max current can not really be defined. EE-318 will give you a good idea on how to calculate the power and current. If your calculation shows that you will need 400 mA, it is always safe to add 50% to that in designing your ower supply. In this case, the worst case in your design is also covered. VDDEXT is also the same. It depends how many IOs are used in DSP and how much current you are drawing from the DSP. Please let us know if you still have problem and need more help.
I will use the DSP21371 at 264MHz so what would be the currnet than, i mean is it smaller when the is running at smaller frequency. About the I/O i am using DPI Pins 1 2 3 4 6 7 8, and DAI pins 1 2 3 & 4. So i have to sum the current responding ot that pins like is in table 3 of EE-318 note?
Yes, in lower core CLK frequencies, power consumption will be lower. Design your power supply so it can deliver 30% more than your circuit consumes so you will be on the safe side. Do the same thing for the VDDEXT
R7 is placed there because the EZ-Kit originally could handle both 21375 and 21371 DSP's. The 21375 DSP pin 19 is NC (no connect) so by DNP'ing R7 (do not populate) the pin is effectively not connected. The 21371 DSP requires pin 31 to be connected to VDDINT, so by placing a 0 ohm resistor between pin 31 and VDDINT, the pin is powered.
Measure the voltage drop across R143 and divide by resistance value to get the current consumption of the VDDINT rail.
Measure the voltage drop across R149 and divide by resistance value to get the current consumption of the VDDEXT rail.
I would caution against sizing your power regulators too closely to the measured value of one EZ-kit. The max rated current consumption (found in datasheet) needs to be taken into acount when determining power needs. IC's power consumption can vary from part to part.
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