• State
  • Locked Locked
  • Replies 8 replies
  • Subscribers 63 subscribers
  • Views 702 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

REG103GA-3.3/2K5 Failure on abrupt application of +12V.

Tim Dunn
Prodigy 100 points
Other Parts Discussed in Thread: REG103

REG103GA-3.3/2K5 on an old design is now failing during abrupt application of +12V.  The 3.3V output is minimally loaded at about 7-10mA.  This hard failure causes VOUT to match VIN which destroys a microcontroller.

With the microcontroller removed, I've reproduced the failure using a 470 ohm resistor.

Using a bench supply set to 12.0V.  REG103GA-3.3 circuit has V enable tied to VIN and C-NR is connected 0.1uF to GND.  Tab is not electrically connected.  VOUT load is 470 ohm resistor and about 10.2uF of capacitance.  The 10uF is ceramic but is about 2 inches of PWB trace away so the ESR should be approaching 100mohms.  

I have also seen the original failure with the 10uF removed and with the NR cap changed to 0.01uF.  

  • 0
    Prodigy 100 points
    I would add that the +12V input has a 10uF ceramic plus quantity 3 ceramic 0.1uF caps including one adjacent to pin 1 (VIN) and 3 (GND) of this SOT223-5 package.
  • 0 in reply to Tim Dunn
    TI__Guru 55940 points
    Hi Tim,

    Is it possible that you have a reverse current event?

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 100 points

    Thanks Ryan.  

    In order to keep any transient reverse current out of the REG103, I added a schottky MBD54 anode to cathode from REG103 output pin 2 to input pin 1.  When I ramp +12V slowly I see the REG103 working as expected into the 470 ohm load.  However when removing the banana jack to the supply and reinserting it, the supply jumps to it's 0.4A current limit setting making Vin fall to about 4V and this REG103 also becomes damaged.  I removed the schottky diode and confirmed that it was still intact with a Vf of 2.95V.

    I have one 2mH leg of a common mode choke in the +12V path.  This should be limiting the rate of rise of +12V as the bench supply caps try to push current into the REG103 input.

    It occurs to me to wonder if the VIN is surging too high on removal of the +12V due to the choke but that's a very low amount of energy in 2mH with just 10mA flowing.

  • 0 in reply to Tim Dunn
    TI__Guru 55940 points
    Hi Tim,

    Is it possible to provide scope shots of Vin, Vout, and if possible Iout on the same scope?

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 100 points

    Here is a Vin Vout trace at the application of +12V.  There is a -12V supply in the system and this creates an initial condition of -0.5V on the REG103 output.

  • 0 in reply to Tim Dunn
    TI__Guru 55940 points
    Hi Tim,

    With this fast of a ramp on Vin, it appears that your Vin did have a fairly significant overshoot. Please note that Abs Max for this device is 16V on the input.

    Very Respectfully,
    Ryan
  • 0 in reply to Tim Dunn
    TI__Mastermind 22610 points
    As a test, is there any way to temporarily eliminate the initial condition of -0.5V on the REG103 output?
  • 0 in reply to Donald Jones
    Prodigy 100 points
    I was able to resolve this issue by adding a 15V zener diode to the REG103 input. The very brief voltage surge is still present but the zener takes the current flow so that the REG103 output starts up as expected with a steady ramp to 3.3V over about 2ms.