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Author Topic: (maybe ) silly Pic-Question about Vdd range ...  (Read 958 times)
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TucoRamirez
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« on: December 05, 2012, 04:50:48 04:50 »

hello,

i was reading on the 16LF88 datasheet ....
Code:
Wide operating voltage range: 2.0V to 5.5V

I'm using a pickit3 chinese clone btw ...  

1:  can i program it (a pdip one) on a 5V only programmer then test it on the 3V battery operated circuit with no risk?

2:  And, in case of using a little 3.3V regulator on the side of a target board (and icsp), i have nothing to touch in the side of the programmer?

3:  there's any stuff concerned with LVP prog stuff here?


thanks in advance.
« Last Edit: December 05, 2012, 05:24:10 05:24 by TucoRamirez » Logged

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FTL
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« Reply #1 on: December 05, 2012, 06:40:22 06:40 »

If I understand you correctly, you are programming it separately from operating it?

If so, since the chip supports 3.3 and 5V supplies it will be fine. You can alternate between voltages any time you want. You can even let it vary from 2 to 5v during operation without a problem.

If you plan to connect the 5V programmer while the 3.3V battery is connected, there could be a problem. There are usually restrictions about bringing any pin up above Vdd by more than one diode drop (0.3V actually). If the programmer raises Vdd and is isolated from the battery (i.e. a diode), there should be no problem. It is OK to have pins below Vdd (as long as they remain above Vss-0.3V).

Edit: Corrected reference to Vcc to be Vss as it should be.
« Last Edit: December 05, 2012, 05:11:39 17:11 by FTL » Logged
TucoRamirez
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« Reply #2 on: December 05, 2012, 08:43:15 08:43 »

ok, now imy confusion is now gone Smiley  that and the one of select the correct intosc frequency against Vcc to avoid surprises when going down from 5V.


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« Reply #3 on: December 05, 2012, 05:18:33 17:18 »

The Intosc frequency is not significantly Dependant on the Vdd supply voltage. It probably does change very slightly as Vdd goes through the operating range of the chip, but it is rated as +/- 1% from 2.5-5.5V.
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sarah90
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« Reply #4 on: December 06, 2012, 07:27:09 19:27 »

If you plan to connect the 5V programmer while the 3.3V battery is connected, there could be a problem. There are usually restrictions about bringing any pin up above Vdd by more than one diode drop (0.3V actually). If the programmer raises Vdd and is isolated from the battery (i.e. a diode), there should be no problem. It is OK to have pins below Vdd (as long as they remain above Vss-0.3V).

When you program while the battery is connected, the pickit3 will sense the voltage and program correctly. If you program without the battery you have tell (configure in the menu) how much voltage the pickit3 should apply. Default there will be no voltage applied by the pickit3 (and it will not detect the pic).
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