Every design is different in terms of
EMI and EMC mitigation, and all designs require their own solution.
- Apply multiple different capacitors for different frequency
range on decoupling circuits. Each capacitor has different ESL, capacitance and
ESR, and different frequency responses.
- Avoid long traces close to radiation sources, and place them
into an internal layer. It is preferred to have ground shielding and add a
termination circuit at the end of the trace.
- TI recommends single ground: SGND. A multilayer such as 4
layers board is recommended so that one solid SGND is dedicated for return
- Use one whole layer (L2) for SGND plane as shown in
Figure 12-1. Use many vias (such as 9 vias) to connect the extended power pad to
the internal SGND plane layer. It is preferred to have the vias close to
AGND pins and DGND pins of the device.
Figure 12-1 Optional
Ground Layer Assignment
- Add LPF on analog signals close to the header connecting the
control card and the power board.
- Do not use a ferrite bead to connect V33A and V33D instead of
using 1-Ω resistor.
- Avoid negative current and negative voltage on all pins.
Schottky diodes may be needed to clamp the voltage; avoid the voltage spike on
all pins to exceed 3.8 V or below –0.3 V; add Schottky diodes on the pins which
could have voltage spikes during surge test; be aware that Schottky diode has
relatively higher leakage current, which can affect the voltage sensing at high
temperatures. The need for external Schottky diodes is conditional. For example,
the DPWM pins only need external Schottky diodes when there is a long distance,
for example, more than 3 inches, between the control card and main power stage
because in this case, the trace can pick up noise and cause electrical
overstress on the device pins. The same is true for GPIO and PMBus pins.
- The auxiliary supply is normally a flyback converter, and its
power transformer can generate a large electromagnetic field which can interfere
with other electronic circuitry. By shielding the primary side windings, the EMI
can be effectively reduced so that the surrounding circuits can have a quieter