• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 1208 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.

LM3414HV instant failure upon powerup

Sid Lori
Prodigy 170 points
Other Parts Discussed in Thread: LM3414HV, LM3414, LM5069, LM5060

I recently started making some LED drivers with the LM3414HV eSO-8, powering 3x 10W LEDs at 33v/664mA from a 55v supply.  (Yes, I know that's not full power into the LEDs.)  Currently, I'm using mostly spec parts (SDR1806-470ML 47µH inductor / 520KHz from a 39K resistor), 2.2µF/100v input filter capacitor,  SS2PH10 diode, 4.7K current limiting resistor, etc.  The only change I made to the circuit is a 10µF, 16v capacitor from VCC to ground, as I am hoping to power a PIC12F1822 for automated dimming control.  (That has not been installed on my boards; there is no load connected to VCC, and nothing connected to the DIM pin.)

Basically, the driver works just fine if I gradually turn up the voltage to 55v, or if I put a 1-ohm resistor in series with input power.  If I directly connect the LED driver to the 55v supply (i.e. like a power switch), the LM3414HV instantly burns out, shorting LX to GND, and 0.14v on VCC.  That has happened with both chips I've tried--and I can easily verify with a multimeter that LX is indeed shorted internally to ground.

 My question: The datasheet specifies a 1µF capacitor from VCC to ground.  I'm suspecting that the use of a 10µF capacitor is overloading and burning out the internal 5.4v regulator, causing a meltdown of the driver MOSFET upon abrupt powerup.  Can someone confirm/deny this? 

If that is indeed the case, I'm assuming that I can use the 1µF capacitor per spec, and use a series resistor to a 10µF capacitor for the PIC.  All I need is a power supply that can power the PIC (i.e. >2v, drawing less than 1mA) for 2 seconds after power is shut off.

  • 0
    TI__Mastermind 25500 points
    Using a 10uF capacitor should be ok and the datasheets simply specifies a minimum of 1uF. The VCC regulator should have a current limit to protect it. In this particular case it is likely overshoot beyond the abs max rating. I have seen it happen often when running near the maximum input voltage. If the slew rate at the input is high enough and/or noisy enough you can easily get overshoot due to parasitic inductances to the board interacting with the input capacitor. If this is a real world condition in the end application you will likely want to protect it with a TVS or a snubber or something else to prevent the overshoot (you could confirm this overshoot with a scope). Maybe just a larger input capacitor value would be enough.
  • 0 in reply to Clinton Jensen
    Prodigy 170 points

    Thanks for your reply.  Yes, this is a real world condition.  The chip's absolute maximum voltage is rated at 65v, and my application will ranges from 44-60v max.  There was a spark when directly connecting the unit up, and I fully understand that that could result in an undesired boost converter through the wiring...which would blow the chip out immediately.  Without a DSO (digital storage oscilloscope)--or enough chips to blow up—I can't determine if it's an overshoot or an undershoot (the latter which could be resolved with a reverse protection diode.)

    That is very interesting to know, as I also purchased some commercial 27W, 60v LED modules from Amazon.  They use a Supertex HV-series controller, and a MOSFET; in typical Chinese style, the diodes (reverse protection, splashback), and MOSFET are all rated at 60v, so it's not safe to run at 60v anyway!  At any rate, I pulled one out of the packaging, connected it up to the system (a battery bank at 52v), and there was a flash and a "crack" from inside--blew a hole in the current sense resistor.  My second power attempt blew a hole through the (450v-rated) Supertex driver.  (I'm suspecting the external 60v MOSFET failed. Interestingly, the 9 3W LEDs are all fine.)  But three other units worked just fine when tested in the same manner.

    What do you suggest for a snubber?  I can't go losing more controllers!

  • 0 in reply to Sid Lori
    TI__Mastermind 25500 points
    A snubber could be designed if you know exactly what the profile will look like which is probably not the case. The safest thing would be to use a 80V or greater schottky for undershoot protection and a TVS for overshoot protection.
  • 0 in reply to Clinton Jensen
    Prodigy 170 points
    I'm not sure how much value a TVS diode would be, as if I choose one rated at 64v (P6SMB75AT3G), it won't clamp a transient until it's between 71-78v (=smoked LM3414). As the maximum system voltage is 60v, I don't think I could use a TVS rated at 58v (P6SMB68AT3G)--but even then, the average clamping voltage is 68v (range 64-71v). Which seems a little above the absolute maximum specification of 65v.

    I think I'll try a 100µF 100v electrolytic capacitor across the input power to the board in addition to the 2.2µF 100v MLCC soldered almost directly to the LM3414.
  • 0 in reply to Sid Lori
    TI__Mastermind 43620 points

    Another option would be to protect the high voltage input with something like the LM5060 or LM5069.

    Regards,

  • 0 in reply to JCHK
    Prodigy 170 points

    It's been a long time, but I can report that the addition of a 100uF, 100v capacitor across the input power leads solved the "blowup problem"; I can make as bad of a connection as I want, and I haven't lost any more LM3414HVs.  But I have lost another one of those 60v Chinese LED fixtures...