DC1903A-B Analog Devices

DEMO MANUAL DC1903A LTM2889 Isolated CAN Module Transceiver Plus Power Description Demonstration circuit 1903A is an isolated CAN Module output voltage on V and communicates all necessary CC2 transceiver plus power featuring the LTM 2889. The demo signaling across the isolation barrier through LTCs isolator circuit features an EMI optimized circuit configuration and Module technology. printed circuit board layout. All components are integrated Design files for this circuit board are available at into the Module isolator. The demo circuit operates from DEMO MANUAL DC1903A o p Demo circuit 1903A is available in two configurations, 3. Board/ground plane size has been minimized. This supporting both versions of the LTM2889. Table 1 details reduces the dipole antenna formed between the logic the demo circuit configurations. side and isolated side ground planes. Table 1 4. Top signal routing and ground floods have been op- timized to reduce signal loops, minimizing differential DEMO CIRCUIT INPUT VOLTAGE DEVICE mode radiation. DC1903A-A 3V to 3.6V LTM2889-3 DC1903A-B 4.5V to 5.5V LTM2889-5 5. Common mode filtering is integrated into the input and output pin headers. Filtering helps to reduce emissions The demo circuit has been designed and optimized for low caused by conducted noise and minimizes the effects RF emissions. Some features of the LTM2889 are not avail- of cabling to common mode emissions. able for evaluation on the demo circuit. The logic supply 6. A combination of low ESL and high ESR decoupling is voltage V is tied to V , and the ON and RE pins are not L CC used. A low ESL ceramic capacitor is located close to available on the input pin header, but may be controlled the module minimizing high frequency noise conduction. by jumpers JP1 and JP3 respectively. EMI mitigation A high ESR tantalum capacitor is included to minimize techniques used include the following: board resonances and prevent voltage spikes due to 1. Four layer PCB, allowing for isolated side to logic side hot plugging of the supply voltage. bridge capacitor. The bridge capacitor is formed between EMI performance is shown in Figure 1, measured using a an inner layer of floating copper which overlaps the logic GHz transverse electromagnetic (GTEM) cell and method side and isolated side ground planes. This structure detailed in IEC 61000-4-20, testing and measurement creates two series capacitors, each with approximately techniques emission and immunity testing in transverse 0.008 of insulation, supporting the full dielectric with- electromagnetic waveguides. stand rating of 2500V . The bridge capacitor provides RMS a low impedance return path for injected currents due 60 to parasitic capacitances of the LTM2889s signal and CISPR 22 CLASS B LIMIT 50 power isolating elements. DC1903AA DC1903AB 40 2. Discrete bridge capacitors (C3, C4) mounted between 30 GND2 and GND. The discrete capacitors provide ad- 20 ditional attenuation at frequencies below 400MHz. 10 Capacitors are safety rated type Y2, manufactured by 0 Murata, part number GA342QR7GF471KW01L, rated DETECTOR = QPEAK 10 RBW = 120kHz for 250V . RMS VBW = 300kHz 20 SWEEP TIME = 17s OF POINTS = 501 30 0 100 200 300 400 500 600 700 800 9001000 FREQUENCY (MHz) DC2889a F01 Figure 1. DC1903A Radiated Emissions dc1903af 2 AMPLITUDE (dBV/m) rinciples perating