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Low Power on C5505 - questions

Todd Anderson78572
Guru 14640 points

All:

I have been tasked with making sure that our C5505 runs at the lowest power possible. So far, I have been able to turn off clocks to several peripherals (which were previously powered). That has helped a LOT. I do have a few questions however:

1. When JTAG is connected (for development), how much does that draw in terms of processor power? (I know on MSP430, to do a valid low-power measurement, the JTAG needs to be disconnected from the circuit.)

2. I think I have implemented the code properly to turn off power to the USB (if necessary), but when I set the bit in the CLKSTOP register to request a stop of USB clock, I do not always get a return Status.

3. During IDLE, there are other items that can be taken inactive, like FFT hardware accelerator. How much does that help with lowering power?

4. If I have disabled clocks to a peripheral, are there other things that must be done to get lower power? I know this is true for USB, but what about an unused I2S port or unused I2C port?

probably more questions to come...

Regards,

Todd Anderson

  • 0
    Guru 14640 points

    All

    When the documentation mentions mW/MHz at 0.15 (1.05 v core) - that is for the core only?

    So, at 60 MHz, that is 9 mW as a starting point.

    Anything peripheral used now adds to that baseline, correct?

    If so, is there a "per peripheral" table that shows what to expect when adding a peripheral (as is found in the C28x datasheet)?

  • 0 in reply to Todd Anderson78572
    Prodigy 220 points

    Hi Todd,

    I've been round this loop about a year ago - as far as I know there are still no datasheet values for the power consumption of the individual peripherials - there is a spreadsheet 'guesstimator' if you haven't seen it here:

    http://www.ti.com/dsp/docs/litabsmultiplefilelist.tsp?sectionId=3&tabId=409&literatureNumber=sprabm0&docCategoryId=1&familyId=325

    The 0.15mW/MHz is just for the core - peripherials are on top of this.  On my board clocking down to 8MHz with UART and I2C I got down to about 8mW - powering off the USB made the biggest chunk of power reduction.  I don't know how your system is operating but an issue I've got on the USB is on the cable detection (I'm using the VBUS comparator to see when the board is plugged into a host) - when the USBPWRD is set to power off the USB it looks like it turns off the VBUS comparator too.  Currently I'm leaving the USB on (burning power) - I think I'm going to poll for a cable plug-in once per second (power up the module, check the comparator then turn it off again if VBUS isn't there)... don't know if you're doing anything similar?

    Dave 

  • 0 in reply to David Whitehouse
    Guru 14640 points

    Thanks for the reply. I will definitely look at the material.