User manual

Board Technical Information
 2010 Microchip Technology Inc. DS51662C-page 51
As stated previously, R25 = 1K and R26 = 330. You can see that without R102 and
R101, V
OUT = 1.25V(1+ 1K/330R) = 5.04V.
For a desired V
OUT, first solve for R2, given R1 = R26 = 330R. Then, knowing R2 and
R25, solve for R102. Determine the nearest available resistor value for R102 and
recalculate the resulting V
DD to make sure it does not exceed the maximum VDD for the
part you will be using.
Table A-23 shows values for R101 and R102 for different V
DD values, assuming that
R25 and R26 on the PICDEM LCD 2 Board are left as their default values of 1K and
330R.
Recommended operating voltages for the various PIMs are:
• PIC18F85J90 and PIC18F87J90 families of devices – 3.3V
• PIC18F8490 family of devices – 5V
• PIC16F917/914 devices – 5V
• PIC16F946 – 5V (when operating on an external 9V DC supply)
• PIC16F1946/7 – 5V
• PIC16LF1946/7 – 3.3V
A.14.2 Slide Switch (S6)
The slide switch allows choosing the BIAS values, either generated by the resistor
ladder, or by the capacitive charge pump. When S6 is switched to the left, the LCDBIAS
pins of the microcontroller are connected to the resistor ladder. When S6 is switched to
the right, the LCDBIAS pins of the microcontroller are connected to the capacitor
network.
TABLE A-23: R101 AND R102 V
DD VALUES
VDD R101 R102
5V Open Open
3.6V Open 1.62K
3.3V Open 1.18K
3.0V Open 866R