Module spare parts UR8AH

Focus on DCS, PLC, robot control system and large servo system.

Main products: various modules / cards, controllers, touch screens, servo drivers.

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9 Power Supply Recommendations The LM3481 is designed to operate from various DC power supply including a car battery. If so, VIN input should be protected from reversal voltage and voltage dump over 48 Volts. The impedance of the input supply rail should be low enough that the input current transient does not cause drop below VIN UVLO level. If the input supply is connected by using long wires, additional bulk capacitance may be required in addition to normal input capacitor. 10 Layout 10.1 Layout Guidelines Good board layout is critical for switching controllers such as the LM3481. First the ground plane area must be sufficient for thermal dissipation purposes and second, appropriate guidelines must be followed to reduce the effects of switching noise. Switch mode converters are very fast switching devices. In such devices, the rapid increase of input current combined with the parasitic trace inductance generates unwanted Ldi/dt noise spikes. The magnitude of this noise tends to increase as the output current increases. This parasitic spike noise may turn into electromagnetic interference (EMI), and can also cause problems in device performance. Therefore, care must be taken in layout to minimize the effect of this switching noise. The current sensing circuit in current mode devices can be easily effected by switching noise. This noise can cause duty cycle jitter which leads to increased spectral noise. Although the LM3481 has 250 ns blanking time at the beginning of every cycle to ignore this noise, some noise may remain after the blanking time. The most important layout rule is to keep the AC current loops as small as possible. Figure 38 shows the current flow of a boost converter. The top schematic shows a dotted line which represents the current flow during onstate and the middle schematic shows the current flow during off-state. The bottom schematic shows the currents we refer to as AC currents. These currents are the most critical currents because current is changing in very short time periods. The dotted lined traces of the bottom schematic are the once to make as short as possible. Figure 38. Current Flow in a Boost Application The PGND and AGND pins have to be connected to the same ground very close to the IC. To avoid ground loop currents attach all the grounds of the system only at one point. A ceramic input capacitor should be connected as close as possible to the Vin pin and grounded close to the GND pin. For a layout example please see AN-2094 LM3481 SEPIC Evaluation Board (SNVA461). For more information about layout in switch mode power supplies refe