Datasheet

PIC32MZ Embedded Connectivity with Floating Point Unit (EF) Family
DS60001320B-page 40 Preliminary  2015 Microchip Technology Inc.
2.9 Designing for High-Speed
Peripherals
The PIC32MZ EF family devices have peripherals that
operate at frequencies much higher than typical for an
embedded environment. Table 2-1 lists the peripherals
that produce high-speed signals on their external pins:
TABLE 2-1: PERIPHERALS THAT
PRODUCE HS SIGNALS ON
EXTERNAL PINS
Due to these high-speed signals, it is important to
consider several factors when designing a product that
uses these peripherals, as well as the PCB on which
these components will be placed. Adhering to these
recommendations will help achieve the following goals:
• Minimize the effects of electromagnetic interference
to the proper operation of the product
• Ensure signals arrive at their intended destination at
the same time
• Minimize crosstalk
• Maintain signal integrity
• Reduce system noise
• Minimize ground bounce and power sag
2.9.1 SYSTEM DESIGN
2.9.1.1 Impedance Matching
When selecting parts to place on high-speed buses,
particularly the SQI bus, if the impedance of the periph
-
eral device does not match the impedance of the pins
on the PIC32MZ EF device to which it is connected,
signal reflections could result, thereby degrading the
quality of the signal.
If it is not possible to select a product that matches
impedance, place a series resistor at the load to create
the matching impedance. See
Figure 2-4 for an
example.
FIGURE 2-4: SERIES RESISTOR
2.9.1.2 PCB Layout Recommendations
The following list contains recommendations that will
help ensure the PCB layout will promote the goals
previously listed.
• Component Placement
- Place bypass capacitors as close to their
component power and ground pins as possible,
and place them on the same side of the PCB
- Devices on the same bus that have larger setup
times should be placed closer to the PIC32MZ EF
device
• Power and Ground
- Multi-layer PCBs will allow separate power and
ground planes
- Each ground pin should be connected to the
ground plane individually
- Place bypass capacitor vias as close to the pad
as possible (preferably inside the pad)
- If power and ground planes are not used,
maximize width for power and ground traces
- Use low-ESR, surface-mount bypass capacitors
• Clocks and Oscillators
- Place crystals as close as possible to the
PIC32MZ EF device OSC/SOSC pins
- Do not route high-speed signals near the clock or
oscillator
- Avoid via usage and branches in clock lines
(SQICLK)
- Place termination resistors at the end of clock
lines
• Traces
- Higher-priority signals should have the shortest
traces
- Match trace lengths for parallel buses (EBIAx,
EBIDx, SQIDx)
- Avoid long run lengths on parallel traces to reduce
coupling
- Make the clock traces as straight as possible
- Use rounded turns rather than right-angle turns
- Have traces on different layers intersect on right
angles to minimize crosstalk
- Maximize the distance between traces, preferably
no less than three times the trace width
- Power traces should be as short and as wide as
possible
- High-speed traces should be placed close to the
ground plane
Peripheral
High-Speed
Signal Pins
Maximum
Speed on
Signal Pin
EBI EBIAx,
EBIDx
50 MHz
SQI1 SQICLK,
SQICSx,
SQIDx
50 MHz
HS USB D+, D- 480 MHz
PIC32MZ
SQI
Flash
Device
50