TDA3MV Datasheet, PDF (186/256 Pages) Texas Instruments – TDA3x SoC for Advanced Driver Assistance Systems (ADAS) 15mm Package (ABF) Silicon Revision 2.0

TDA3MV, TDA3MA
TDA3LX, TDA3LA
SPRS964C – JUNE 2016 – REVISED JULY 2017
www.ti.com
8.2.6 EMI / EMC Issues Prevention
All high-speed digital integrated circuits can be sources of unwanted radiation, which can affect nearby
sensitive circuitry and cause the final product to have radiated emissions levels above the limits allowed
by the EMC regulations if some preventative steps are not taken.
Likewise, analog and digital circuits can be susceptible to interference from the outside world and picked
up by the circuitry interconnections.
To minimize the potential for EMI/EMC issues, the following guidelines are recommended to be followed.
8.2.6.1 Signal Bandwidth
To evaluate the frequency of a digital signal, an estimated rule of thumb is to consider its bandwidth f_BW
with respect to its rise time, t_R:
f_BW ≈ 0.35 / t_R
This frequency actually corresponds to the break point in the signal spectrum, where the harmonics start
to decay at 40 dB per decade instead of 20 dB per decade.
8.2.6.2 Signal Routing
8.2.6.2.1 Signal Routing—Sensitive Signals and Shielding
Keep radio frequency (RF) sensitive circuitry (like GPS receivers, GSM/WCDMA, Bluetooth/WLAN
transceivers, frequency modulation (FM) radio) away from high-speed ICs (the device, power and audio
manager, chargers, memories, and so forth) and ideally on the opposite side of the PCB. For improved
protection it is recommended to place these emission sources in a shield can. If the shield can have a
removable lid (two-piece shield), ensure there is low contact impedance between the fence and the lid.
Leave some space between the lid and the components under it to limit the high-frequency currents
induced in the lid. Limit the shield size to put any potential shield resonances above the frequencies of
interest; see Figure 8-8, Typical Impedance Profile of a Capacitor.
8.2.6.2.2 Signal Routing—Outer Layer Routing
In case there is a need to use the outer layers for routing outside of shielded areas, it is recommended to
route only static signals and ensure that these static signals do not carry any high-frequency components
(due to parasitic coupling with other signals). In case of long traces, make provision for a bypass capacitor
near the signal source.
Routing of high-frequency clock signals on outer layers, even for a short distance, is discouraged,
because their emissions energy is concentrated at the discrete harmonics and can become significant
even with poor radiators.
Coplanar shielding of traces on outer layers (placing ground near the sides of a track along its length) is
effective only if the distance between the trace sides and the ground is smaller that the trace height above
the ground reference plane. For modern multilayer PCBs this is often not possible, so coplanar shielding
will not be effective. Do not route high-frequency traces near the periphery of the PCB, as the lack of a
ground reference near the trace edges can increase EMI: see Section 8.2.6.3, Ground Guidelines.
8.2.6.3 Ground Guidelines
8.2.6.3.1 PCB Outer Layers
Ideally the areas on the top and bottom layers of the PCB that are not enclosed by a shield should be
filled with ground after the routing is completed and connected with an adequate number of vias to the
ground on the inner ground planes.
186 Applications, Implementation, and Layout
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