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louwi_138
Joined: 17 Nov 2012
Posts: 23
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| low power pic18f4550 - ccs pcb 4.110 |
 Posted: Sat Nov 17, 2012 8:26 pm |
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Hello 
I want to run my uc with 3.3V.
So should I just put 3.3V in power pins or I should write some code in the uc ? |
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WingNut
Joined: 04 Nov 2012
Posts: 6
Location: NC
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| Posted: Sat Nov 17, 2012 10:27 pm |
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| We can't advise you if you don't tell us what PIC your using. |
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andrewg
Joined: 17 Aug 2005
Posts: 316
Location: Perth, Western Australia
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| Posted: Sun Nov 18, 2012 12:23 am |
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This is the difference between an 18F4550 and an 18LF4550 - "F" vs "LF". If you read the data sheet (always a good idea), you'll find under section "28 Electrical Characteristics" that the "F" chip has a minimum 4.2V. The "LF" is a little more complicated. Lowering the voltage means lowering the maximum clock speed. At 3.3V the maximum clock speed is ~25MHz.
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Andrew |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19260
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| Posted: Sun Nov 18, 2012 3:02 am |
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Max clock at at 3.3v, is 18.7MHz with the LF.
Also, if you want to use USB, _you_ have to generate Vusb. The minimum for the internal regulator to generate this is again the 4.2v.
Consider a different chip. Same comment about you having to generate Vusb, but a chip like the 18F46J50, operates at the full 48MHz at 3.3v, is pin compatible, and offers extra features (faster ADC, second USART, etc. etc.... Draws typically about 1/3rd the power as well.
Best Wishes |
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