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TEA1771 датащи(PDF) 5 Page - NXP Semiconductors |
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TEA1771 датащи(HTML) 5 Page - NXP Semiconductors |
5 / 25 page TEA1771_1 © NXP B.V. 2009. All rights reserved. Product data sheet Rev. 01 — 6 February 2009 5 of 25 NXP Semiconductors TEA1771 GreenChip PC primary control IC 8. Functional description 8.1 Introduction The TEA1771 is designed to cooperate with the TEA1781 and the TEA1782 secondary side controllers in a forward converter topology, see Figure 11. A typical application area of this converter is a power supply for a desktop PC. The topology supported by the TEA1771 enables transformer resetting using an active reset mechanism. For this purpose a reset switch in the form of a lateral IGBT has been integrated into the IC. This reset switch can operate high-side using an external boost capacitor. Advantage of this active reset mechanism is, compared to a third winding solution, that a higher maximum duty cycle (> 50%) can be achieved. Reducing dissipation by recovering energy is another advantage of the reset mechanism when compared to the standard R/C/D topology. The TEA1771 has a feed-forward control regulation, avoiding high resonant voltage peaks as a result of output load or input voltage transients. 8.2 Supply At power-up, the primary and secondary ICs are not yet supplied via the auxiliary windings as the main switch M1 is off, see Figure 11. Initially, before start-up, the primary IC is in Charge mode and supplies itself with a current Ich(LVIN) from the high voltage pin DM2, see the SUPPLY block in Figure 1. The voltage on pin DM2 is equal to the input voltage in this static situation. It is connected to the input via the transformer and the parallel diode of the reset switch, Drst, see Figure 11. In Charge mode LVIN is charged from DM2 via an internal current source, Ich(LVIN). From LVIN the nodes DECVCC and DECPVCC are supplied by internal regulators. As a result, when LVIN is charged, the DECVCC and DECPVCC nodes, which are decoupled by external capacitors, are charged simultaneously. This is illustrated in the left part of Figure 3. When the voltage at LVIN reaches its start level Vstartup(LVIN) and the voltage on pin VRST is in its start-up window, the IC enters Running mode and starts switching; see M1 signal in Figure 3. The voltage on pin VRST is in the start-up window when the voltage on pin VRST is between the minimum start voltage, Vstart(VRST)(min), and the maximum start voltage, Vstart(VRST)(max). These start-up conditions are pointed out in the STATE DIAGRAM block in Figure 1. If the logic signal VVRSTOK is high, the voltage VVRST is in the start-up window. n.c 22 not connected CB 23 boost capacitor DM1 24 drain main switch (M1) Table 3. Pin description …continued Symbol Pin Description |
Аналогичный номер детали - TEA1771 |
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Аналогичное описание - TEA1771 |
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