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UCC3580D-1 Datasheet(PDF) 7 Page - Texas Instruments |
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UCC3580D-1 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 18 page 7 UCC1580-1,-2,-3,-4 UCC2580-1,-2,-3,-4 UCC3580-1,-2,-3,-4 Output Configurations The UCC3580 family of ICs is designed to provide con- trol functions for single ended active clamp circuits. For different implementations of the active clamp approach, different drive waveforms for the two switches (main and auxiliary) are required. The -3 and -4 versions of the IC supply complementary non-overlapping waveforms (OUT1 and OUT2) with programmable delay which can be used to drive the main and auxiliary switches. Most active clamp configurations will require one of these out- puts to be transformer coupled to drive a floating switch (e.g. Figure 5). The -1 and -2 versions have the phase of OUT2 inverted to give overlapping waveforms. This con- figuration is suitable for capacity coupled driving of a ground referenced p-channel auxiliary switch with the OUT2 drive while OUT1 is directly driving an n-channel main switch (e.g. Figure 4). The programmable delay can be judiciously used to get zero voltage turn-on of both the main and auxiliary switches in the active clamp circuits. For the UCC3580, a single pin is used to program the delays between OUT1 and OUT2 on both sets of edges. Figure 1 shows the relationships between the outputs. Figure 2 gives the ratio between the two delays. During the transition from main to auxiliary switch, the delay is not very critical for ZVS turn-on. For the first half of OUT1 off-time, the body diode of the auxiliary switch conducts and OUT2 can be turned on any time. The transition from auxiliary to main switch is more critical. Energy stored in the parasitic in- ductance(s) at the end of the OUT2 pulse is used to dis- charge the parasitic capacitance across the main switch during the delay time. The delay (Delay 1) should be op- timally programmed at 1/4 the resonant period deter- mined by parasitic capacitance and the resonant inductor (transformer leakage and/or magnetizing induc- tances, depending on the topology). However, depend- ing on other circuit parasitics, the resonant behavior can change, and in some cases, ZVS turn-on may not be ob- tainable. It can be shown that the optimum delay time is independent of operating conditions for a specific circuit and should be determined specifically for each circuit. APPLICATION INFORMATION (cont.) Figure 4. Active clamp forward converter. UDG-95071-2 |
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