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Propeller 2 core current draw (1.8v) — Parallax Forums

Propeller 2 core current draw (1.8v)

TubularTubular Posts: 4,622
edited 2013-08-19 02:05 in Propeller 2
I'm looking into a regulator to suit the P2, to drop the 3v3 down to 1.8v for its core.

Anyone know what kind of worst case current draw I could expect on the 1.8v (core) rail?

I'm thinking something like a MCP1727 in a SOIC-8 pack to begin with.

Comments

  • BigFootBigFoot Posts: 259
    edited 2013-02-12 19:40
    I was going to use Ti's TPS 77318 for the 1.8 volt supply but after reading Chips assessment on the power consumption
    for the P2 chip realized that a more powerful regulator was required.
  • jmgjmg Posts: 15,148
    edited 2013-02-12 20:53
    Tubular wrote: »
    I'm thinking something like a MCP1727 in a SOIC-8 pack to begin with.

    Looks quite good, reasonable price and margin, and has a proper Reset signal.
    I would layout for the Adjustable version, initially, as often first silicon has different voltage sweet spots...
    Looks to be an easy change.
  • TubularTubular Posts: 4,622
    edited 2013-02-12 21:14
    Thanks for checking, jmg. Yes I put the adjustable version down so the voltage can be tweaked a little bit as required.

    I'm not really sure whether there are other regulators compatible in the same footprint - they seem to have subtle differences in soic8 pinout. But I'll go with it for now until advised otherwise.

    I've pretty well finished a breakout board design and hope to send it off to the fab next week when they are back from new year holidays. Just the basics onboard - xtal, regulator, flash, prop plug
  • TubularTubular Posts: 4,622
    edited 2013-02-12 21:21
    BigFoot wrote: »
    I was going to use Ti's TPS 77318 for the 1.8 volt supply but after reading Chips assessment on the power consumption
    for the P2 chip realized that a more powerful regulator was required.

    Hi BigFoot,

    Did Chip already mention something about it? Perhaps I missed it.

    I vaguely recall some mention of the leakage currents involved, but I'm more after the maximum operating current draw, which will depend on frequency of course. It'll also help me decide whether to hang the 1v8 regulator under the 3v3 one (likely) or run it separately from the 5v incoming...
  • jmgjmg Posts: 15,148
    edited 2013-02-12 21:42
    Tubular wrote: »
    Just the basics onboard - xtal, regulator, flash, prop plug

    I would also suggest doing an option for Xtal or Oscillator module, like a 5mm x 3.2mm FOX924B TCXO.- those are high precision, and come from 10MHz to 27MHz, which is outside the Prop 1 range...
  • TubularTubular Posts: 4,622
    edited 2013-02-12 22:05
    Jmg,

    That's a really nice part. I didn't know they did such nice things in such small packages. I'll add the supply rails to the other 2 pins.

    As it happens I could only fit a 5x3.2 xtal near the prop2 anyway, plus there are also XI and XO pins broken out maybe 4cm away, with the ability to cut the tracks to the broken out pins if required.

    Thanks for the advice.
  • SeairthSeairth Posts: 2,474
    edited 2013-02-13 05:11
    Tubular wrote: »
    Did Chip already mention something about it?

    Big foot may have been referring to this post: http://forums.parallax.com/showthread.php/125543-Propeller-II-update-BLOG?p=1162345&viewfull=1#post1162345

    Assuming Chip's estimate is accurate, then a 1.5A regulator seems like a good start.
  • BigFootBigFoot Posts: 259
    edited 2013-02-13 08:18
    Seairth wrote: »
    Big foot may have been referring to this post: http://forums.parallax.com/showthread.php/125543-Propeller-II-update-BLOG?p=1162345&viewfull=1#post1162345

    Assuming Chip's estimate is accurate, then a 1.5A regulator seems like a good start.

    Yes, that is the post. He mentioned 1.5 Watts which is allot by today's standards and is going to make it difficult to use the chip
    in battery powered applications. I have always thought that the P2 would be awesome to use for a quad copter and hope he was
    talking about absolute maximum power consumption.
  • TubularTubular Posts: 4,622
    edited 2013-02-13 12:46
    Ok, the 1.5watts at 1.8 volts means the current draw is around 0.83A, which presents a few design challenges. I was hoping to follow a simple microUSB powered, LDO design, and while this is still possible, it's clear that switching regulator design is going to be the way to go down the track.

    Ordinary USB can only supply 0.5A / 2.5 watts, not enough to power Prop2 without a switching reg. I can use a 1.0 Amp wall wart like used for the Pi, samsung phone chargers, ipads etc (1 amp /5 watts)

    The MCP1727 still appeals, but its SOIC-8 package thermals at 150 C per watt are out of the question.

    The DFN version of the MCP1727 (3x3mm, with exposed pad and vias underneath) is 41 degrees per watt, resulting in a 57 degree temperature rise for the 5v to 3v3 regulation, and 51 degree rise for the 3v3 to 1v8 regulator. That's burn territory so I'll try spreading the heat out with a pcb heatsink and see if we can get that well down.

    And I guess start looking at suitable switcher solutions too
  • jmgjmg Posts: 15,148
    edited 2013-02-13 13:13
    Tubular wrote: »
    The DFN version of the MCP1727 (3x3mm, with exposed pad and vias underneath) is 41 degrees per watt, resulting in a 57 degree temperature rise for the 5v to 3v3 regulation, and 51 degree rise for the 3v3 to 1v8 regulator.
    Sounds good, spread them apart and use maximal copper, and thicker copper too.

    Note that current spec will be all COGs at full speed, which is a rare combination So an Analog regulator should comfortably deliver the peak, but typical use will have much lower average powers.

    There is a little bit of voltage margin from 5V to 3v3, so adding (say) 2 x 1206 1 ohm (or less) resistors, spreads that thermal load a little and gives you a nice means to check the actual current.
  • jmgjmg Posts: 15,148
    edited 2013-02-14 17:54
    Tubular wrote: »
    And I guess start looking at suitable switcher solutions too

    The ideal here is a part that work from under 5V, and up to plug-pack regions, and has PowerGood, and avoids an external Schottly.
    Dual would be nice, but they seem to be quite a jump in price.

    The Richtek RT7250BZSP is ADJ 2A 8SOP, Stocked at DigiKey, 25 : $0.6244, and frees you to choose anything for the 3v3 side.
    - so looks a good match for Prop 2 ?
  • TubularTubular Posts: 4,622
    edited 2013-02-15 09:36
    jmg,

    that looks like a nice and well priced part.

    For now I think I'll measure the temp rise on the MCP1727's by simulating the1.5 watt core loading with the board I just posted. I figure the power rail arrangement (node-gnd-3v) means 7805 switching regulator replacements (cui inc at up to 2 amps, but no 1v8, or recom 5v to 1v8) are easy to fit and add external smoothing caps to.

    It would be easy enough to try a Richtek based plugin board in the same format, and then perhaps revise the main breakout board accordingly. I think that's how I'm going to tackle it.

    Great work digging out these useful parts...
  • tonyp12tonyp12 Posts: 1,950
    edited 2013-03-01 17:50
    Just hit the market, adjustable output. Enable and Power Good
    AP717xx.jpg
    http://www.mouser.com/ProductDetail/Diodes-Inc/AP7175MP-13/?qs=sGAEpiMZZMv4Mmfa%252bK8JIj5e7r4%252b51XfB6ybjpS8c94%3d
    33cents for 100 units (Wow!)

    the AP7176B can handle Vin of 5.5v but a little harder to find at the moment.
  • NumPyNumPy Posts: 27
    edited 2013-03-26 18:29
    Forgive me if I havent done my homework here. I have searched the forums and the docs but I dont see a figure for the lowest possible power in a "sleep" mode. I think the P1 was around 5 micro amps. Is there a value for the P2 yet?
  • NumPyNumPy Posts: 27
    edited 2013-03-27 02:25
    0.5mA per MIPS (MIPS = Freq in MHz / 4 * Number of Active Cogs)

    I believe this is the correct spec for P1
  • LeonLeon Posts: 7,620
    edited 2013-03-27 03:01
    The supplies might need to be sequenced. Does anyone know if that is the case?
  • cgraceycgracey Posts: 14,133
    edited 2013-03-27 15:45
    Leon wrote: »
    The supplies might need to be sequenced. Does anyone know if that is the case?

    It doesn't matter, as long as the I/O supply is within 50ms of the core 1.8V supply.

    For our little module, we found a nice Micrel part that is only 2x2mm and uses one 1uH inductor and two 4.7uF 0603 caps to regulate 1.8V@2A:

    Micrel.png


    The minimum current draw of the Prop2 will probably by about 1mA because of leakage.

    Chip
    Micrel.png
    916 x 421 - 27K
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2013-03-27 15:57
    cgracey wrote: »
    It doesn't matter, as long as the I/O supply is within 50ms of the core 1.8V supply.

    For our little module, we found a nice Micrel part that is only 2x2mm and uses one 1uH inductor and two 4.7uF 0603 caps to regulate 1.8V@2A:

    Micrel.png


    The minimum current draw of the Prop2 will probably by about 1mA because of leakage.

    Chip

    Great, I need to make some final adjustments and that part looks good at around a buck. Are there any other hard and fast figures available yet (or maybe not so hard and fast).
  • tonyp12tonyp12 Posts: 1,950
    edited 2013-08-14 16:05
    This seems like a nice part, two 800mA for heavy duty work and 2 ldo for noise free analog work etc.
    LFCSP24.jpg
    http://www.mouser.com/ProductDetail/Analog-Devices/ADP5037ACPZ-3-R7/?qs=sGAEpiMZZMtitjHzVIkrqYThiPHWFX9axPSzmoXpPc8%3d
  • TubularTubular Posts: 4,622
    edited 2013-08-19 02:05
    I really like a lot of the AD stuff. It's a bit on the expensive side but nicely designed.

    You're right about the ldo for analog, but that'd be at 3v3, so guess you'd have to feed both an ldo and a switcher off say a 3v7 or above rail...
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