"Pump" Your PICkit 2's VPP

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PICkit2Dev
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2008/06/16 13:10:04 (permalink)
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"Pump" Your PICkit 2's VPP

The VPP (programming voltage) charge pump on PICkit 2 units supplies limited current at 12 Volts.
Older "Black Button" units can only supply about 3 mA.
Newer "Red Button" units can supply about 6 mA.
(The exact threshold will depend on component tolerances in a particular unit).

This is sufficient to program any circuit following the ICSP guidelines in Chapter 3 of the PICkit 2 User's guide. (The exception being the new PIC16F72x parts with some Black Button units.)  However, there might be situations where an abnormally heavily load is present on the VPP pin, such as an older board not following the ICSP design guidelines.  In these situations it can be very helpful to be able to supply more current from the PICkit 2 VPP pin.

The PICkit 2 may be modified to supply up to about 13-15 mA at 12 Volts from VPP.  This modification applies to all PICkit 2 units (Red & Black button).
To increase the charge pump current capability, replace the 3 components at the following reference designators with these new components:

R21 - replace with 0603 510 Ohm 5% Resistor

L1 - replace with Murata LQH43MN681J03L   (available from Mouser)

C15 - replace with 68uF 10% 20V Tantalum cap, such as Kemet T491D686K020AT (available from Mouser)
NOTE: If you only need 10-12mA, replacing C15 is not necessary.

Please note that this modification is purely optional, and is posted solely for information purposes for those interesting in tinkering with their PICkit 2 unit.
post edited by PICkit2Dev - 2008/06/16 13:12:11
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    hycom
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    RE: "Pump" Your PICkit 2's VPP 2008/06/17 02:38:52 (permalink)
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    Please note that this modification is purely optional, and is posted solely for information purposes for those interesting in tinkering with their PICkit 2 unit.

    So that means, this change will never go into new PK2s ?
    (Perhaps the one with the Green Button )



    p-brane resident
    #2
    xiaofan
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    RE: "Pump" Your PICkit 2's VPP 2008/06/17 07:21:21 (permalink)
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    I agree with you that this is good to have for next hardware revision of PICkit 2.

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    #3
    dchisholm
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    RE: "Pump" Your PICkit 2's VPP 2008/06/17 08:13:57 (permalink)
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    ORIGINAL: PICkit2Dev

    . . . This is sufficient to program any circuit following the ICSP guidelines in Chapter 3 of the PICkit 2 User's guide. . . . However, there might be situations where an abnormally heavily load is present on the VPP pin, such as an older board not following the ICSP design guidelines . . .
    Analyzing from a slightly different perspective (please correct me if I'm wrong here):
    • With the exception of the 16F72x series, no PIC processor draws more than 3 mA from Vpp while being programmed.
    • The initial release version of the PICKit2 can supply 3 mA (nom) from Vpp.
    • The revised PICKit2 can supply 6 mA.  That allows 3 mA, over and above the actual programming current, to supply application circuitry connected to the MCLR/Vpp pin.
    • The modifications described here can increase the Vpp capability to at least 10 mA, perhaps 15 mA.  At least 7 mA (and perhaps as much as 12 mA) can be available for driving any stuff the user has connected to MCLR/Vpp.
    I'm curious what sort of practical application circuitry might be connected to MCLR, that draws more than a couple mA of current during programming.  (I realize Vpp is more than 5V, typically 10V - 15V, during programming.)  This pin can only be an input, so there won't be an LED, or transistor base circuit, hung on MCLR.  For many years, Microchip has warned against direct (no pullup resistance) connections from MCLR to Vdd - and even a modest pullup resistance of 2K ohms would keep the Vpp current within the 6 mA limit - so what kinds of networks might draw significant current from Vpp?

    Also - The First Rework Instructions for the PICKit2 changed R21 to 1K ohms (but didn't mention the previous value).  I presume this accounts for the increase in Vpp capability from 3 mA to 6 mA.  The current set of rework instructions reduces R21 to 510 ohms, and changes other energy storage components in the power converter.  Since resistors and electrolytic capacitors are MUCH more likely to be FOB (Found On Bench) than miniature drum-core inductors, can you suggest practical limiting values (minimum R21 and maximum C15) that can be used with the original L1?

    Dale
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    PICkit2Dev
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    RE: "Pump" Your PICkit 2's VPP 2008/06/17 09:08:27 (permalink)
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    With the exception of the 16F72x series, no PIC processor draws more than 3 mA from Vpp while being programmed.

    It is, of course, important to consider any external components as well as the need to drive parasitic capacitance and still meet the Programming Specification rise time. 

    Thus, I would not really agree with these statements:


  • The revised PICKit2 can supply 6 mA.  That allows 3 mA, over and above the actual programming current, to supply application circuitry connected to the MCLR/Vpp pin.
  • The modifications described here can increase the Vpp capability to at least 10 mA, perhaps 15 mA.  At least 7 mA (and perhaps as much as 12 mA) can be available for driving any stuff the user has connected to MCLR/Vpp.


  • While a steady-state current of 3mA may possibly be "available" the effect of additional loads on inrush current and rise time may be much more significant.

    I would strongly recommend against intentional additional loading of VPP during programming.  Instead, it might be useful as a quick, low-power 12V supply using the Tools > Troubleshoot... dialog to turn on VPP.  Make sure the Midrange/Standard or PIC18F family is selected to get 12V.

    can you suggest practical limiting values (minimum R21 and maximum C15) that can be used with the original L1?


    Dropping R21 from 1K to 510 Ohm by itself gains around an additional 800uA.  I would not suggest going any lower, as it starts to pull a lot of extra current from the USB supply.  The original value was 10K.

    I don't think increasing C15 with the existing L1 will have much of any effect, and would not recommend it.  Increasing C15 creates its own set of problems.
     
     
     
     
    (hycom)
    So that means, this change will never go into new PK2s ?

     
    If there is another critical issue requiring a hardware update, it may be looked into.  However, it adds little value in and of itself for the vast majority of users to justify the expense of changing a product.
     
     
    post edited by PICkit2Dev - 2008/06/17 09:16:47
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    dchisholm
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 10:24:55 (permalink)
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    ORIGINAL: PICkit2Dev

    I would strongly recommend against intentional additional loading of VPP during programming.
    That's not what I had in mind.  I was more interested in knowing what sort of circuit-design things I might have done to the MCLR/Vpp pin that unintentionally loaded it to the point where program loading became problematical.

    Instead, it might be useful as a quick, low-power 12V supply using the Tools > Troubleshoot... dialog to turn on VPP.  Make sure the Midrange/Standard or PIC18F family is selected to get 12V.
    That's a clever idea!  I'll start composing a standard answer for Forum posts such as:
    ORIGINAL: The_Most_Humbly_Magnificent_XBox_Champ_of_the_Galaxy

      ! ! ! !   URGENT   ! ! ! !

    I am improving my game console with a PIC to create some new sound effects.  To get the volume I need, the sounds play back through 17 LM741 op-amps connected in parallel and powered from the Vpp voltage on the PICKit2 . . . .


    Dale
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    DarioG
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 13:39:00 (permalink)
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    LOL grin nice one!

    quando a trump ci prende il CANCRAZZO è sempre troppo tardi.
    #7
    PICkit2Dev
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 15:52:22 (permalink)
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    I was more interested in knowing what sort of circuit-design things I might have done to the MCLR/Vpp pin that unintentionally loaded it to the point where program loading became problematical.
    I'm curious what sort of practical application circuitry might be connected to MCLR, that draws more than a couple mA of current during programming.  (I realize Vpp is more than 5V, typically 10V - 15V, during programming.)  This pin can only be an input, so there won't be an LED, or transistor base circuit, hung on MCLR.  For many years, Microchip has warned against direct (no pullup resistance) connections from MCLR to Vdd - and even a modest pullup resistance of 2K ohms would keep the Vpp current within the 6 mA limit - so what kinds of networks might draw significant current from Vpp?

     
    OK.  I misunderstood - apparently didn't read it carefully enough.
     
    So, hopefully, you haven't done anything to highly load VPP wink but some examples of problematic circuits include:
    Design with 1K pullup on MCLR, especially with 3.3V VDD (12-3.3 / 1K = ~9mA)
    In addition to pullup on MCLR, circuit has large cap from MCLR to GND. (and no isolation R or diode).
    Improperly isolated external reset circuit (such as CPU monitor or watchdog) that activates during programming.
     
    I looked into this to address a specific issue that an FAE came across, and thought I would post the modification in case anyone else found it useful.
     
    #8
    FunnyNYPD
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 16:03:33 (permalink)
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    ORIGINAL: PICkit2Dev
    So, hopefully, you haven't done anything to highly load VPP wink but some examples of problematic circuits include:
    Design with 1K pullup on MCLR, especially with 3.3V VDD (12-3.3 / 1K = ~9mA)
    In addition to pullup on MCLR, circuit has large cap from MCLR to GND. (and no isolation R or diode).
    Improperly isolated external reset circuit (such as CPU monitor or watchdog) that activates during programming.

    I looked into this to address a specific issue that an FAE came across, and thought I would post the modification in case anyone else found it useful.

    If 1K is too "small", what's a good pull-up resistor value you recommend?
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    PICkit2Dev
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 16:54:11 (permalink)
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    If 1K is too "small", what's a good pull-up resistor value you recommend?


    Please see Chapter 3 "Using ICSP" of the PICkit 2 User's Guide, and the ICSP Guide
    post edited by PICkit2Dev - 2008/06/18 16:56:31
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    FunnyNYPD
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 17:50:02 (permalink)
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    So a 10 Kohm is recommended. Thanks.
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    xiaofan
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 18:40:05 (permalink)
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    Last time there were many circuits using 10k/10nF combination for the MCLR pin. Some uses 10k/100nF. These circcuits do not have isolation diode or resistor like the circuit in the PICkit 2 user guide.
     
    This kind of circuit can pose problems for programmers with low Vpp driving capability like PICkit 2. Programmers like PM3 should have no problems with them.

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    #12
    FunnyNYPD
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    RE: "Pump" Your PICkit 2's VPP 2008/06/18 20:05:11 (permalink)
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    1k is too "small", 10K creats issues, so what's the best value in a real world?
    #13
    BruceTElliott
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    RE: "Pump" Your PICkit 2's VPP 2008/06/19 00:39:10 (permalink)
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    I've been using 10K with and (mostly) without an isolating diode for years with no problems (ICD2, Real Ice, Pickit2).
    Of course, good software never needs to be reset ... ;-)
    #14
    xiaofan
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    RE: "Pump" Your PICkit 2's VPP 2008/06/19 05:02:09 (permalink)
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    ORIGINAL: FunnyNYPD

    1k is too "small", 10K creats issues, so what's the best value in a real world?


    Hmm, 10k has no issues. 100nF is the issue here if no isolation diode/resistor is used.

      USB_Links and libusb
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    PICkit2Dev
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    RE: "Pump" Your PICkit 2's VPP 2008/06/19 08:23:33 (permalink)
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    Yes, the issue is not the 10K, it's the direct cap to ground.  When using a cap, it should be isolated per the ICSP documents mentioned above.
    #16
    dchisholm
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    RE: "Pump" Your PICkit 2's VPP 2008/06/19 11:53:46 (permalink)
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    ORIGINAL: DarioG

    LOL grin nice one!
    It's good to know that at least TWO people appreciate my work!  (You also co-operated with "drh" on another of my recent efforts.)

    Dale
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    dchisholm
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    RE: "Pump" Your PICkit 2's VPP 2008/06/19 12:10:19 (permalink)
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    ORIGINAL: PICkit2Dev

    OK.  I misunderstood - apparently didn't read it carefully enough . . .

    . . . I looked into this to address a specific issue that an FAE came across, and thought I would post the modification in case anyone else found it useful.
    Thanks for sharing that info!  I thoroughly enjoy anything that's close to "hardware-hacking", though 0603 component packages make it a lot less fun than playing with the Dynaco Stereo 70.  (On the other hand, the PICKit2 can't make you bounce upon your buttocks in a decidedly non-professional manner.)

    There's a PICKit2 floating around my client's lab someplace.  I've never actually used it - I'm thoroughly attached to my ICD2 - but the more I hear about the PICKit2, the more I want to give it a try.

    As you see, your post generated some good discussion and created a thread that'll probably get pointed to in the future.  Thanks again!

    Dale
    #18
    FunnyNYPD
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    RE: "Pump" Your PICkit 2's VPP 2008/06/19 12:19:59 (permalink)
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    The PICkit 2 is definitely worth every penny you spend. Hope it will support the old dsPIC30Fs very soon.

    #19
    pswsm
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    RE: "Pump" Your PICkit 2's VPP 2008/06/27 01:05:52 (permalink)
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    May I suggest that before doing the suggested hardware changes that the start up Vpp error with some devices is sorted out first.
     
    I have both an ungraded old black button PicKit and the new red button PicKit. They both give the same error message at start up when connected to different chips even through the circuit board has not changed and older version of the PicKit applications software works.
     
    I have found that the 16f690 on the LCDemo board is programed ok but when I try to program a smd 16f690 in circuit on pcb the PicKit comes up the error. Similarly before version 2.5 I had not trouble programing a 16f946 smd decive in circuit on a pcb board. Further programing a 12f675 smd on a breadboard worked fine but the same circuit with no changes on pcb the device gives the Vpp error.
     
    I have an ICD2 that programs all the devices ok
     
    #20
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