PicKit3 smoke with low pin count demo board

[manicdoc]

Hi,

Thought I'd just relate a story - I've decide to have a crack at building a robot and using PIC's as the 'middle layer' between sensors/etc and a Raspberry PI. I've programmed PIC's before by an old dedicated parallel port based programmer no problem.

So got myself some PIC's and the PicKit3 programmer with the LPC demo board to give myself a 'gentle' way into this new in circuit programming for me..  Well followed the instructions (as best as I could, someone at microchip needs a kick up the bum to make it into real instructions that actually make sense as a whole). So had the board running its default LED race quite nicely. got the PicKit3 targeted to the PIC on the board, everything seen and set up in the IDE - so went and plugged the PicKit3 into the LPC and everything was recognizing fine - hit program and it got part way and complained about something not being set to what it expected, put the power supply to the board up to exactly 5v (as I'd read elsewhere under supplying a PIC can cause troubles) and then tried again and BANG! literally - one fired PicKit3, magic smoke and all...

Now I've raised a support ticket with microchip and fully expect to get a replacement as I haven't got a clue what I did wrong and I suspect a hardware fault. Everything physically was by the book and plugged in the right way round etc as far as I could make out.

In the future I'm not going to touch their the LPC board and build from scratch myself complete with some aggressive current limiting. Back to basics.

In a word annoying...

Just thought I'd share this and if anybody has some advice on if there is anything else I can do to 'protect' the PicKit3. Also let me know if you think I did something silly.

David: If you want to check out the 'corpse', I'll be at the Home Maker Centre Castle Hill tomorrow.

[David_AVD]

Sounds like you may have connected something up in an incorrect manner.  Without an accurate diagram or picture of the setup in question it's hard to say more.

[manicdoc]

Hi David,

It was literally just the LPC board as is, Vdd and Ground hooked up to a 5v bench power source and the PicKit3 hooked up to the on board connector, with the PicKit3 hooked up via USB to the computer - bog standard as out of the box; and the demo preloaded on the PIC worked fine against the same 5v supply... Hence why it came as such a shock that it went bang.

When I get time I'm going to test the LPC board and see what was going on.. the PIC is rated to 5.5v (not LF)

I know everyone needs to blow up a few things once in a while, need to recycle the smoke, just expected it to be somewhat later... I've ordered myself another Pickit3 and I'll do it my way by the numbers rather than trusting a demo board - so much for a short cut with this.

[David_AVD]

Post a picture of the uncased PicKit3 board (both sides) and the circumstances leading to the smoke may be evident.

[adam1213]

Well followed the instructions (as best as I could, someone at microchip needs a kick up the bum to make it into real instructions that actually make sense as a whole

Please suggest this to Microchip directly if you have not already. Preferably in a slightly more polite way.

[JVR]

Aparrantly you did not read the warning message issued by MPLAB prior to connecting to the PICkit3.

You either had the micro connected to 5V prior to connecting the PK3, or connected 5V after the PK3 was connected. Either way, you did not check the settings supplied and my guess is that the PK3 tried to power the LPC board with 3.3V, while being backfed 5V, boom goes the regulator.

[manicdoc]

Aparrantly you did not read the warning message issued by MPLAB prior to connecting to the PICkit3.

You either had the micro connected to 5V prior to connecting the PK3, or connected 5V after the PK3 was connected. Either way, you did not check the settings supplied and my guess is that the PK3 tried to power the LPC board with 3.3V, while being backfed 5V, boom goes the regulator.

Possible, but the PK3 was set not to supply, quite sure of that. I remember going in and checking and setting it to 5v as well just in case... Anyway's I'm chalking this one up to experience and going from the ground up and ultra safe. Its all a learning opportunity 

[JVR]

That it is.

Just download the PK3 schematics and fix the broken bits. Ive fixed my PK2 and PK3's a few times due to stupidity

[Jon Chandler]

Possible, but the PK3 was set not to supply, quite sure of that. I remember going in and checking and setting it to 5v as well just in case... Anyway's I'm chalking this one up to experience and going from the ground up and ultra safe. Its all a learning opportunity 

I think you're missing the point....

If the PICkit is connected to a powered circuit but not to USB, the PICkit micro's pins will be exposed to greater than 0.3 volts (the maximum permitted is Vdd + 0.3 volts) which could damage the chip.

I just noticed this warning a few days ago in the PICkit 2 documentation.  Makes sense if you happen to think about it.

[David_AVD]

If the PICkit is connected to a powered circuit but not to USB, the PICkit micro's pins will be exposed to greater than 0.3 volts (the maximum permitted is Vdd + 0.3 volts) which could damage the chip.

Interesting.  I'm pretty sure I've unplugged my PicKit3 from the USB occasionally with them still plugged into the (powered) target.  Haven't killed one yet.

[hans]

I've killed my PICKIT2 (I know, not same, but very similar analog design I believe) with the logic analyser tool. I had a MCU powered from it, was probing some SPI signals with it, and didn't trigger at all. I pulled what I believed to be my trigger signal from the board and started poking around. I had it set to trigger when it sees a '0' (CS line). So I thought: does it work at all? Let's connect it to ground.

It just so happens 1 data signal and power are located next to each other. So I ofcourse picked the wrong one. Why? Because I didn't use the right color of wiring from the PICKIT2 connector on my breadboard.
Because the PICKIT2 software was 'BUSY' and polling for a trigger, the software protection for overvoltage, current limiting etc. didn't work. After holding the wire for 2 seconds some magic smoke came out.

I burned a N/P-MOSFET SOT23-6 chip for switching the VDD target power and a schottky diode. I replaced them and it still works today, although the voltage output calibration is incorrect because I couldn't be bothered to place a similarly specced diode in there. Recalibrating doesn't help because of a higher voltage drop under load.

I am uncertain whether PICKIT3 has this bug too, but it is certainly a possibility (and fault from MCH) that there is no protection on the pickit rails if the software is so called 'busy'.


If I connect to a self-powered target, I force the software to never power the target. I don't want the software to figure out anymore whether it needs to supply power or not - I want to be consent of my own test setup.

[ivan747]

Here's a rant. Using the PICKit 3 standalone software (it is necessary when not using MPLAB) I set my voltage to 3V to power a prototype with a PIC and an expensive LCD display. The device selected was the wrong PIC, so I click the drop down menu, select the corresponding PIC18F22K26 and the goddamn thing switches to supply the maximum voltage that part handles, 5V! That POS nearly destroyed my LCD that takes weeks (and $20) to ship to this country.