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SX-Key USB Warm around the coil — Parallax Forums

SX-Key USB Warm around the coil

william chanwilliam chan Posts: 1,326
edited 2008-09-03 16:03 in General Discussion
I like the blue LED light on my new SX-Key during programming.

But I find the area near the coil gets warm after about 20 secs plugged into USB port, even when it is not programming anything.

Is this normal? Now I keep it unplugged from USB when not in use.

I think the SX28 chip on the SX-Key could be continuously generating Vpp voltages when it is supposed to be idle.
How to make it cool down?

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www.fd.com.my
www.mercedes.com.my

Comments

  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2008-09-02 16:30
    William,

    I left an SX-Key USB connected to a USB port for about 30 minutes. It got moderately warm around the SX20 chip and the coil (about 40° C = 104° F). I don't think the coil is producing much heat. Most of it is generated by the SX 20 running at a 32 MHz clock, and the clock generator chip with a 20 MHz master clock.

    You are right, Vpp is generated continuously but not fed through to the OSC1 pin, thus almost no current is drawn from the Vpp source when the Key is idle, so the coil should not heat up normally.

    Nice to hear that you like the blue LED. It is turned on as long as comminication is established between the SX-Key USB and the SX-Key IDE. In a former firmware version, I had the LED flicker while programming a chip was in progress. Maybe, this additional gimmic will be re-introduced in a later firmware version.

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    Greetings from Germany,

    Günther
  • william chanwilliam chan Posts: 1,326
    edited 2008-09-03 00:56
    Why the SX Blitz USB does not warm up like the SX-Key USB?

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    www.fd.com.my
    www.mercedes.com.my
  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2008-09-03 16:03
    On the SX-Blitz USB, only the FTDI 232R chip is powered from the USB port, where the SX20 is powered from the target system. IOW when you keep the Blitz connected to a USB port only but do not connect it to a target system, the SX20 is not powered, and thus does not dissipate heat.

    When designing the SX-Key USB circuit, I decided to power all components from the USB port. This allows to isolate the Vdd signals on the Key from the target, so that targets with Vdd < 5V can be programmed/debugged w/o an extra adapter you will need for the SX Blitz to do programming.

    On the other hand, the SX-Key USB puts much more load on the USB port than the Blitz, so you better do not connect the Key to a passive USB hub. Use one of the PC's USB ports, or one on an active hub, i.e. one with its own power supply.

    This may be the reason why the designer of the SX-Blitz USB has decided to only power the FTDI232R from the USB port.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Greetings from Germany,

    G
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