DM163030 Microchip Technology, DM163030 Datasheet - Page 50

• Manufacturer Part Number: DM163030
• Description: KIT DEV PICDEM LCD2
• Manufacturer: Microchip Technology
• Series: PICDEM™r
• Type: MCUr

Specifications of DM163030

• Contents: Evaluation Board
• Processor To Be Evaluated: PIC18F85J90
• Interface Type: RS-232
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: PIC18F8493
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PICDEM™ LCD 2 Demonstration Kit User’s Guide
DS51662C-page 50
A.14.1
The PICDEM LCD 2 board features an adjustable voltage regulator, the venerable
LM317. It is U3 on the board, and can be recognized by the SO-223 package on the
upper left side. Nearby, there is a header, J10, and two resistors, R25 and R26. R25
and R26 are used to set the output voltage of the LM317. By default, R25 = 1K and
R26 = 330R, which results in an output voltage of 5.0V.
The reason an adjustable voltage regulator is provided is so that the PICDEM LCD 2
Demonstration Board can be used with a wide range of LCD PIC microcontrollers. The
PIC18FXXJ90 family of devices tolerates a maximum V
PIC18FXX90, PIC16F91X and PIC16F946 tolerate a maximum V
adjustable voltage regulator allows a different V
and PIC18F and PIC16F LCD devices.
The switching between 3.6V and 5.5V parts is very convenient. The plug-in module
boards are populated with the R101 and R102, appropriately, according to the proces-
sor module requirement which mates with the daughter board/emulator header that
surrounds the ICE module (U1A). J10 on the PICDEM LCD 2 board is intended to con-
nect with the 3-pin header on the plug-in module. This allows the resistors, R101 and
R102, on the plug-in module to be connected in parallel to the resistors, R25 and R26.
This way V
soldered onto the plug-in module.
The plug-in module is prepopulated with the values shown in Table A-22:
TABLE A-22:
For V
(1% resistors are recommended for precise adjustment of V
Now, let’s look at how to determine R101 and R102 if a different V
it is a good idea to look at the data sheet for the LM317 to understand how the voltage
is adjusted. We will not duplicate all the details here. The following equation is taken
from an LM317 data sheet:
EQUATION A-1:
I
V
and adjustment terminal.
That gives us the following equation:
EQUATION A-2:
PIC18F87J90
PIC18F85J90
PIC18F8490
PIC16F914/917
PIC16F946
PIC16F1946/7
PIC16LF1946/7
ADJ
REF
is minimized by the LM317, so it can be assumed to be zero or at least very small.
V
V
R2 = R25 || R102 = (R25* R102)/(R25+R102)
R1 = R26 || R101.= (R26* R101)/(R26+R101)
DD
=1.25V; it is the reference voltage developed by the LM317 between the output
OUT
OUT
Module
= 3.3 volts, R101 can be left unpopulated and R102 can be 1.18K.
= V
= 1.25V(1+R2/R1)
Using the Adjustable Voltage Regulator
DD
REF
can automatically be adjusted to the voltage appropriate to the part
PIM PREPOPULATED VALUES
(1+ R2/R1) + I
R101
Open
Open
Open
Open
Open
Open
Open
ADJ
* R2
DD
to be provided for PIC18FJ devices
1.18K
1.18K
1.18K
R102
Open
Open
Open
Open
DD
 2010 Microchip Technology Inc.
of 3.6V, whereas the
DD
.)
DD
DD
of 5.5V. The
is desired. First,
3.3V
3.3V
5.0V
5.0V
5.0V
5.0V
3.3V
V
DD