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Power Consumption Question

MixedSignal
Prodigy 220 points

SLVA401 document shows the various power supply options for the C5505.

I notice that the 1.05V supply calls for about 600mA current, and the 3.3V requires about 500mA.

These numbers not make sense compared to the Data Sheet, which specs currents in the mA and tens of mA range.

Can someone from TI explain how we should size our power supplies? If we believe the Data Sheet, we'd be looking at, say, 0.22mW/MHz which is 22mA at 100MHz, and a few other supplies with a few mA.

How did the author of SLVA401 come to suggest over 1A of current supply capability between 3.3V and 1.05V supplies?

I also received a spreadsheet for computing power consumption, and that doesn't call out such high currents either.

I don't know if you're assuming we're driving some large external memory bus at 100MHz?

 

  • 0
    TI__Intellectual 2530 points

    Hi,

    The higher numbers that you mentioned represent the maximum values that the power devices may have to support in a system.  C5505 specific information is in the last column on page 2 of SLVA401.  The information in the datasheet is the right information for C5505, and it is consistent with the information in that last column.

    Best regards, Vishal

  • 0 in reply to Vishal Markandey
    Prodigy 220 points

    Thanks Vishal, I had an out of date copy of the document that did not have the last column in the same detail. This helps.

    However, I cannot find any information in the Data Sheet on current consumption for USB power supplies (USB3V3 and USB1V3) or EMIF power supplies. In SLVA401A, these are specified as very high (300mA and 245mA). I also looked at the Excel spreadsheet and it does not provide any current consumption values for these supplies.Can you give us some info on what the C5505 needs from these supplies?

    I also see in SLVA401A Page 2 that they suggest an LDO for the 1.3V USB supply to reduce noise. This is extremely inconvenient. We'd like to just use one Buck converter for all the 1.3V supplies to keep things simple. Will the USB not work well if powered that way?

    Thanks in advance for your input.

  • 0 in reply to MixedSignal
    TI__Expert 8065 points

    We are working on getting power numbers for all different IOs. Once we have it then we will release the informaiton to TI Web.

    Regarding to the section question, using USB_LDO for the USB core is nothing to do with noise. It may refer to clean power source from LDO... Anyway, yes you can use external 1.3V for all 1.3V supplies including USB core. 

    Regards,

    Peter Chung

     

  • 0 in reply to Peter Chung
    Prodigy 220 points

    Thanks Peter.

    Until you figure out the power consumption on the IO power supplies, how should we size these supplies? To provide 605mA limits our options on PSU chips compared to, say 200mA, which I would imagine is certainly sufficient given how low power the C5505 is generally.

    Thanks.

  • 0 in reply to MixedSignal
    TI__Expert 8065 points

    I can't give you clear answer to it. First of all, I need to know your usage case in detail and then run the same usage case on the C5505 or C5515 EVM and measure the maximum current drawing. For hardware design, I think you should consider maximun current drawing, not average current. The number we are working on is to proivde averge currents for different usage cases. 

    FYI, we have C5515 EVM and C5505EVM schematic availa on the following links. You may want to check them out.

    http://support.spectrumdigital.com/boards/evm5515/revb/

    http://support.spectrumdigital.com/boards/evm5505/revd/

    I hope this helps.

    Best Regards,

    Peter Chung