DC1746A-A Linear Technology, DC1746A-A Datasheet - Page 2

• Manufacturer Part Number: DC1746A-A
• Description: EVALUATION KIT LOW EMI LTM2881-3
• Manufacturer: Linear Technology
• Series: µModuler

Specifications of DC1746A-A

• Main Purpose: Interface, Transceiver RS-422/RS-485
• Embedded: No
• Utilized Ic / Part: LTM2881
• Primary Attributes: 3V Supply, Isolated, Transceiver + Power
• Kit Contents: Board, Datasheet
• Tool / Board Applications: Interface-Backplane, PCI, PCI Express, RS-XXX, Digital & Opto Isolator
• Mcu Supported Families: LTM2881
• Development Tool Type: Hardware - Eval/Demo Board
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Secondary Attributes: -

DEMO MANUAL DC1746A
OPERATING PRINCIPLES
EMI mitigation techniques used include the following:
1. Four layer PCB, allowing for isolated side to logic side
2. Discrete bridge capacitors (C3, C4) mounted between
3. Board/ground plane size has been minimized. This
2
‘bridge’ capacitor. The bridge capacitor is formed be-
tween an inner layer of fl oating copper which overlaps
the logic side and isolated side ground planes. This
structure creates two series capacitors, each with ap-
proximately 0.008" of insulation, supporting the full
dielectric withstand rating of 2500V
capacitor provides a low impedance return path for
injected currents due to parasitic capacitances of the
LTM2881’s signal and power isolating elements.
GND2 and GND. The discrete capacitors provide ad-
ditional attenuation at frequencies below 400MHz.
Capacitors are safety rated type Y2, manufactured by
Murata, part # GA342QR7GF471KW01L.
reduces the dipole antenna formed between the logic
side and isolated side ground planes.
RMS
–10
–20
–30
60
50
40
30
20
10
Figure 1. DC1746A Radiated Emissions
0
0
. The bridge
100 200 300 400 500
DC1746A-B
FREQUENCY (MHz)
CISPR 22 CLASS B LIMIT
DETECTOR = QuasiPeak
RBW = 120kHz
VBW = 300kHz
SWEEP TIME = 17s
# OF POINTS = 501
4. Top signal routing and ground fl oods have been opti-
5. Common mode fi ltering is integrated into the input
6. A combination of low ESL and high ESR decoupling is
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”.
600 700 800 900
mized to reduce signal loops, minimizing differential
mode radiation.
pin header and output DB9 connector. Filtering helps
to reduce emissions caused by conducted noise and
minimizes the effects of cabling to common mode
emissions.
used. A low ESL ceramic capacitor is located close to
the module minimizing high frequency noise conduction.
High ESR tantalum capacitors are included to minimize
board resonances and prevent voltage spikes due to hot
plugging of the input supply voltage.
DC1746A F01
1000
dc1746af