NXP Semiconductors
IMXRT500HDG
i.MX RT500 Hardware Design Guide
7.5 Trace impedance requirements
The trace impedance requirements for the MIMXRT595-EVK PCB were developed with
the board vendor who provided guidance based on the signal impedance requirements.
•
Except for critical impedance traces, we specified minimum trace widths of 4.0 mils and
minimum spaces of 5.0 mils.
•
For 50 ohm impedances, most single-ended high-speed traces with 4.5 mil widths over
the 2.7 mil dielectric are used.
•
For the USB 90 ohm differential impedance, 4.5 mil widths with 5 mil spaces over the
2.7 mil dielectric are used.
•
The 100 ohm differential impedance for the
MIPI_DSI
signals uses 3.5 mil widths with
7 mil spaces.
•
Additionally, the minimum via diameter of 8mils with an 18 mil pad is used for most
high-speed signals.
MIMXRT595-EVK PCB requirements determined with board vendor, see
:
•
Minimum trace width of 4.0mils and minimum space of 5.0 mils, except for certain
critical impedance traces.
•
50 ohm impedance for most single-ended high-speed traces (use 4.5 mil widths over
2.7 mil dielectric).
•
90 ohm differential impedance for some differential pair traces, like USB (use 4.5 mil
widths and 5 mil spaces).
•
100 ohm differential impedance for other differential pair traces, like MIPI_DSI (use 3.5
mil widths and 7 mil spaces).
•
Dielectric thicknesses of 2.7 mils to 4.0 mils.
•
Minimum via diameter of 8mils with 18 mils pad.
Layers
Trace width
(Mils)
Single ended
L1_TOP
L3 and L4
L6_BOTTOM
4.5
4.5
4.5
50
50
50
4.5
4.5
4.5
5
5
5
90
90
90
3.5
3.5
3.5
7
7
7
100
100
100
Impedance
(Ohms)
Trace width
(Mils)
Single ended
Impedance
(Ohms)
Trace width
(Mils)
Trace spacing
airgap
(Mils)
Differential
Impedance
(Ohms)
Trace width
(Mils)
Trace spacing
airgap
(Mils)
Differential
Impedance
(Ohms)
Trace width
(Mils)
Trace spacing
airgap
(Mils)
Differential
Impedance
(Ohms)
Figure 17. Trace impedance requirements
7.6 General high-speed routing recommendations
It is a general recommendation for high-speed routing, we may overstate the term high-
speed routing, but it has been proven that when all signals are routed as high-speed
signals, the system has better electrical and EMC performance.
High-speed signals (memory buses, serial interfaces, clock signals, and so on) must
have defined return current paths (typically on an adjacent reference plane). Trace length
and impedance control are required to achieve correct communication among high-speed
devices, consider perfect eye diagrams for USB serial data. While low-speed signals do
not necessarily require a reference plane to direct return currents, these signals can be
affected by switching noise or radiating electromagnetic energy without a reference.
High-speed signals must not cross gaps in the reference plane. Gaps cause signal return
discontinuities that cause reflections.
IMXRT500HDG
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User guide
Rev. 0 — 15 November 2022
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