Datasheet

 2011-2013 Microchip Technology Inc. DS70657G-page 27
dsPIC33EPXXXGP50X, dsPIC33EPXXXMC20X/50X AND PIC24EPXXXGP/MC20X
2.0 GUIDELINES FOR GETTING
STARTED WITH 16-BIT
DIGITAL SIGNAL
CONTROLLERS AND
MICROCONTROLLERS
2.1 Basic Connection Requirements
Getting started with the dsPIC33EPXXXGP50X,
dsPIC33EPXXXMC20X/50X and
PIC24EPXXXGP/MC20X families requires attention
to a minimal set of device pin connections before
proceeding with development. The following is a list
of pin names, which must always be connected:
•All V
DD and VSS pins
(see Section 2.2 “Decoupling Capacitors”)
•All AV
DD and AVSS pins (regardless if ADC module
is not used)
(see Section 2.2 “Decoupling Capacitors”)
•V
CAP
(see Section 2.3 “CPU Logic Filter Capacitor
Connection (V
CAP)”)
•MCLR
pin
(see Section 2.4 “Master Clear (MCLR) Pin”)
• PGECx/PGEDx pins used for In-Circuit Serial
Programming™ (ICSP™) and debugging purposes
(see Section 2.5 “ICSP Pins”)
• OSC1 and OSC2 pins when external oscillator
source is used
(see Section 2.6 “External Oscillator Pins”)
Additionally, the following pins may be required:
•V
REF+/VREF- pins are used when external voltage
reference for ADC module is implemented
2.2 Decoupling Capacitors
The use of decoupling capacitors on every pair of
power supply pins, such as V
DD, VSS, AVDD and
AV
SS is required.
Consider the following criteria when using decoupling
capacitors:
• Value and type of capacitor: Recommendation
of 0.1 µF (100 nF), 10-20V. This capacitor should
be a low-ESR and have resonance frequency in
the range of 20 MHz and higher. It is
recommended to use ceramic capacitors.
• Placement on the printed circuit board: The
decoupling capacitors should be placed as close
to the pins as possible. It is recommended to
place the capacitors on the same side of the
board as the device. If space is constricted, the
capacitor can be placed on another layer on the
PCB using a via; however, ensure that the trace
length from the pin to the capacitor is within
one-quarter inch (6 mm) in length.
• Handling high-frequency noise: If the board is
experiencing high-frequency noise, above tens of
MHz, add a second ceramic-type capacitor in
parallel to the above described decoupling
capacitor. The value of the second capacitor can
be in the range of 0.01 µF to 0.001 µF. Place this
second capacitor next to the primary decoupling
capacitor. In high-speed circuit designs, consider
implementing a decade pair of capacitances as
close to the power and ground pins as possible.
For example, 0.1 µF in parallel with 0.001 µF.
• Maximizing performance: On the board layout
from the power supply circuit, run the power and
return traces to the decoupling capacitors first,
and then to the device pins. This ensures that the
decoupling capacitors are first in the power chain.
Equally important is to keep the trace length
between the capacitor and the power pins to a
minimum, thereby reducing PCB track
inductance.
Note 1: This data sheet summarizes the
features of the dsPIC33EPXXXGP50X,
dsPIC33EPXXXMC20X/50X and
PIC24EPXXXGP/MC20X families of
devices. It is not intended to be a
comprehensive reference source. To
complement the information in this data
sheet, refer to the related section of the
“dsPIC33E/PIC24E Family Reference
Manual”, which is available from the
Microchip web site (www.microchip.com)
2: Some registers and associated bits
described in this section may not be
available on all devices. Refer to
Section 4.0 “Memory Organization” in
this data sheet for device-specific register
and bit information.
Note: The AV
DD and AVSS pins must be
connected independent of the ADC
voltage reference source.