Hello, Tamas, I hope some analog guru can join the discussion and give some precise current/voltage analysis. I and my team don't see that happen in the past year. Also we could check with the members here see if something similar happened and how they fixed the issue. So, please don't worry too much. Best wish, Funny N. New Bedford, MA http://www.AuElectronics.selfip.com ----- Original Message ---- From: Tamas Rudnai To: Microcontroller discussion list - Public. Sent: Wednesday, January 23, 2008 5:47:55 AM Subject: Re: [PIC] PICkit2 for 3.3V chips Hi Funny, Yes, I understand this part, my worries was around the current withdrawn from the 2550 pins RA2, RA3 and RA4. If VUSB is +5V and VDD_TGT is 3V, then there is a 2V that Q3 and Q5 drops through R14 and R19. That would have been 200mA each (and also there is the AUX, so that it would have been 600mA together). And what I did not quite like is the way it works, as obviously there is no 200mA on that resistor. According to what people say on that link Xiaofan mentioned, it's "only" around 25mA, as this circuit exploits the 2550's output gate: As the current increases, the voltage on the output pin drops - lower output voltage, smaller difference in between the Vdd_TGT and the line, therefore lower current has to be dissipating. The 3 lines, PGC, PGD and PGM (or AUX) consumes 3x25mA, plus I am not sure about the efficiency of Vpp pump, but I assume it needs a lot too, so I was worry if PicKit2 consumes near to the limit of the 100mA USB spec? That external power source capability is definitely looks good especially because of this :-) Thanks Tamas On Jan 23, 2008 2:34 AM, Funny NYPD wrote: > Hi, Tamas, > As far as I understood, the PGD and PGC voltage are regulated by Q3, Q5 > and a clamp reference voltage on PICKit2 design. It is done in a old analog > way. > > We has a schematic might help express the design concept better: > http://www.auelectronics.selfip.com/CB0703_PICKit2_Schematic.pdf > > Also on our web site: "FAQ->Q5-> section 6.2 and 6.3" there is a test of > 3.3V on PGD and PGC; > http://www.auelectronics.selfip.com/Q5.htm > > You should be able to repeat those test with your PICKit2 and take some > measurement with your scope. If possible please let us know what you found. > > You can also test lower voltage, such as a 2.5V, if your last voltage > selection on step 4 is 2.5V. > > regards, > > Funny N. > New Bedford, MA > http://www.AuElectronics.selfip.com > > > > ----- Original Message ---- > From: Tamas Rudnai > To: Microcontroller discussion list - Public. > Sent: Tuesday, January 22, 2008 7:13:35 PM > Subject: Re: [PIC] PICkit2 for 3.3V chips > > Thanks Funny for the info, > > Vdd was ok, I was just scratching my head about the PGD/PGC line - signal > level also has to be regulated and that is quite tricky and simple in the > same time on PicKit2, but was not sure if I can trust on that. Olin's > solution is the opposite - not quite simple but reliable - the price of > that > device is higher though, and the purpose is a bit different. > > Tamas > > > On Jan 22, 2008 11:23 PM, Funny NYPD wrote: > > > Hi, Tamas, > > You are welcome! > > > When PicKit2 programs a 3.3V part, it reduces the Vdd to 3.3V, that's > > > fine, that's done by a PWM driven PN dual mosfet. > > >From what I understood, the 3.3V is regulated by U2 and Q1, the control > > signal of U2 and Q1 is from the PIC18F2550. > > The dual PN mosfet U6 is used for turning on/off power supply to > external > > circuit, and protect the power supply from possible short-circuit. > > The N MOSFET on U6 could also be used to detect exist of external power, > > on some case, this will trigger PICkit2 turn it own Vdd off > automatically > > when external Vdd is found. > > > > Funny N. > > New Bedford, MA > > http://www.AuElectronics.selfip.com > > > > > > > > ----- Original Message ---- > > From: Tamas Rudnai > > To: Microcontroller discussion list - Public. > > Sent: Tuesday, January 22, 2008 2:15:44 PM > > Subject: Re: [PIC] PICkit2 for 3.3V chips > > > > Thanks Xiaofan and Funny, > > > > I think I will use PicKit2 for 5V parts only - I would not like to rely > on > > such a parameter. Olin's USBprog is definitely impressive - the only > > drawback I can see now is that it does not support debugging, but that's > a > > programmer, anyway. > > > > Thanks, > > Tamas > > > > > > > > > > On Jan 22, 2008 2:45 PM, Funny NYPD wrote: > > > > > Hi, Tamas, > > > I remember Microchip support has a very good answer on this question > on > > > "google pickit2 group". Please let me know if you cannot find the > > answer. > > > Some member of PIClist also joined this discussion on the "google > > pickit2 > > > group". > > > > > > Regards, > > > > > > Funny N. > > > New Bedford, MA > > > http://www.AuElectronics.selfip.com > > > > > > > > > > > > ----- Original Message ---- > > > From: Tamas Rudnai > > > To: Microcontroller discussion list - Public. > > > Sent: Tuesday, January 22, 2008 6:06:49 AM > > > Subject: [PIC] PICkit2 for 3.3V chips > > > > > > Hi All, > > > > > > Looking at the PicKit2 schematics, there is one very interesting to > see. > > > When PicKit2 programs a 3.3V part, it reduces the Vdd to 3.3V, that's > > > fine, > > > that's done by a PWM driven PN dual mosfet. But was wondering what > > happens > > > with the PGC/PGD/PGM lines. It can be seen that each line has a 10R > > > resistor > > > and a bipolar that puts the exceeding voltage to the ground. As 10R is > > far > > > too small, too much current would have been taken out from the pin I > was > > > wondering how it works. > > > > > > It turned out, that the output pin of a pic drops the voltage down by > > > withdrawing too much current from it. Therefore as the current > increases > > > the > > > voltage decreases, so less and less current will be flown through on > > that > > > 10R resistor. > > > > > > The question is that is this a sufficient way to limit voltage on > output > > > pin? It seems so weird for me but maybe it was the easiest way to do > > that. > > > Any thoughts? > > > > > > Thanks, > > > Tamas > > > -- > > > http://www.piclist.com PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > > > > > > > > > ____________________________________________________________________________________ > > > Never miss a thing. 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