Operating Principles - Linear Technology DC1794A Demo Manual

DEMO MANUAL DC1794A

operAting principles

EMI mitigation techniques used include the following:
1. Board/ground plane size has been minimized. This
reduces the dipole antenna formed between the logic
side and isolated side ground planes.
2. Top signal routing and ground floods have been opti-
mized to reduce signal loops, minimizing differential
mode radiation.
3. A high ESR tantalum capacitor is included to minimize
board resonances and prevent voltage spikes due to
hot plugging of the input supply voltage.
2
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4. Optional discrete bridge capacitors (C3, C4) can be
mounted between GND2 and GND. The discrete ca-
pacitors provide additional attenuation at frequencies
below 300MHz as shown in Figure 1. Capacitors are
safety rated type Y1, manufactured by Vishay, part #
VY115K31Y5SQ63V0.
EMI performance is shown in Figure 1, measured using
a Gigahertz Transverse Electromagnetic (GTEM) cell and
method detailed in IEC 61000-4-20, "Testing and Mea-
surement Techniques—Emission and Immunity Testing
in Transverse Electromagnetic Waveguides".
60
50
40 CISPR 22 CLASS B LIMIT
30
20
10
0
DETECTOR = QuasiPeak
–10
RBW = 120kHz
VBW = 300kHz
–20
SWEEP TIME = 17s
# OF POINTS = 501
–30
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (MHz)
Figure 1. DC1794A Radiated Emissions
DC1794A F01
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