DEMO MANUAL DC1747A LTM2882: Dual Isolated RS232 Module Transceiver + Power DESCRIPTION Demonstration circuit 1747A is a dual isolated RS232 on V . The part generates the output voltage V and CC CC2 Module transceiver with integrated power featuring communicates all necessary signaling across the isola- the LTM 2882. The demo circuit provides a 2-chan- tion barrier using Linear Technologys isolator Module nel, 2500V , galvanically isolated RS232 transceiver technology. RMS interface. The demo circuit features an EMI optimized Design les for this circuit board are available at circuit con guration and printed circuit board layout. All DEMO MANUAL DC1747A OPERATING PRINCIPLES The logic supply voltage V is tied to V on the demo 3. Minimized board/ground plane size. This reduces the L CC circuit. The ON pin and the spare logic channel DIN to dipole antenna formed between the logic side and DOUT, connected to DE, are selectable by jumper pro- isolated side ground planes. gramming only. 4. Optimized top signal routing and ground oods to reduce EMI mitigation techniques used include the following: signal loops, minimizing differential mode radiation. 1. Four layer PCB, allowing for isolated side to logic side 5. Common mode ltering integrated into the input pin bridge capacitor. The bridge capacitor is formed be- header and output DB9 connector. Filtering helps to tween an inner layer of oating copper which overlaps reduce emissions caused by conducted noise and the logic side and isolated side ground planes. This minimizes the effects of cabling to common mode structure creates two series capacitors, each with ap- emissions. proximately 0.008 of insulation, supporting the full 6. A combination of low ESL and high ESR decoupling. dielectric withstand rating of 2500V . The bridge RMS A low ESL ceramic capacitor is located close to the capacitor provides a low impedance return path for module minimizing high frequency noise conduction. injected currents due to parasitic capacitances of the High ESR tantalum capacitors are included to minimize LTM2882s signal and power isolating elements. board resonances and prevent voltage spikes due to hot 2. Discrete bridge capacitors (C3, C4) mounted between plugging of the input supply voltage. GND2 and GND. The discrete capacitors provide ad- EMI performance is shown in Figure 1, measured using ditional attenuation at frequencies below 400MHz. a Gigahertz Transverse Electromagnetic (GTEM) cell and Capacitors are safety rated type Y2, manufactured by method detailed in IEC 61000-4-20, Testing and Mea- Murata, part GA342QR7GF471KW01L. surement Techniques Emission and Immunity Testing in Transverse Electromagnetic Waveguides. 60 DETECTOR = QuasiPeak, R = 120kHz, BW 50 V = 300kHz, SWEEP TIME = 17s BW NUMBER OF POINTS = 501 40 30 20 10 0 10 CISPR 22 CLASS B LIMIT 20 DC1747A-B DC1747A-A 30 0172 3 4 5698 10 FREQUENCY (MHz) DC1747A F01 Figure 1.DC1747A Radiated Emissions dc1747af 2 dBV/m