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LT1941 数据表(PDF) 18 Page - Linear Technology |
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LT1941 数据表(HTML) 18 Page - Linear Technology |
18 / 24 page 18 LT1941 1941f In Figure 6a, a larger capacitor on RUN/SS2 delays chan- nel 2 with respect to channel 1. The soft-start capacitor on RUN/SS2 should be at least twice the value of the capacitor on RUN/SS1. A larger ratio may be required, depending on the output capacitance and load on each channel. Make sure to test the circuit in the system before deciding on final values for these capacitors. The circuit in Figure 6b requires the fewest components, with both channels sharing a single soft-start capacitor. The power good comparator of channel 1 disables chan- nel 2 until output 1 is in regulation. For independent control of channel 2, use the circuit in Figure 6c. The capacitor on RUN/SS1 is smaller than the capacitor on RUN/SS2. This allows the LT1941 to start up and enable its power good comparator before RUN/SS2 gets high enough to allow channel 2 to start switching. Channel 2 only operates when it is enabled with the external control signals and output 1 is in regulation. The circuit in Figure 6a leaves both power good indicators free. However, the circuits in Figures 6b and 6c have another advantage. As well as sequencing the two outputs at start-up, they also disable channel 2 if output 1 falls out of regulation (due to a short circuit or a collapsing input voltage). Finally, be aware that the circuit in Figure 6d does not work, because the power good comparators are disabled in shutdown. PCB LAYOUT For proper operation and minimum EMI, care must be taken during printed circuit board (PCB) layout. Figure 7 shows the high current paths in the step-down regulator circuit. Note that in the step-down regulators large, switched currents flow in the power switch, the catch diode and the input capacitor. In the inverter/boost regulator large, switched currents flow through the power switch, the switching diode, and either the output capacitor in boost configuration, or the tank capacitor in the inverter configu- ration. The loop formed by these components should be as small as possible. Place these components, along with the inductor and output capacitor, on the same side of the circuit board and connect them on that layer. Place a local, unbroken ground plane below these components and tie this ground plane to system ground at one location, ideally at the ground terminal of the output capacitor C2. Addi- tionally, keep the SW and BOOST nodes as small as possible. APPLICATIO S I FOR ATIO OFF 1941 F06 RUN/SS1 PG1 ON GND OFF RUN/SS1 LT1941 LT1941 ON GND RUN/SS2 OFF RUN/SS1 ON OFF2 ON2 GND RUN/SS2 RUN/SS2 VC2 PG1 1nF 1nF 1nF 2.2nF 1nF 1.5nF 1.5nF (6b) Fewest Components (6c) Independent Control of Channel 2 OFF RUN/SS1 ON GND RUN/SS2 PG1 (6d) Doesn't Work ! (6a) Channel 2 is Delayed LT1941 LT1941 Figure 6. Several Methods of Sequencing Two Ouputs. Channel 1 Starts First |
类似零件编号 - LT1941 |
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类似说明 - LT1941 |
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