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TEA1781T Scheda tecnica(PDF) 9 Page - NXP Semiconductors |
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TEA1781T Scheda tecnica(HTML) 9 Page - NXP Semiconductors |
9 / 32 page TEA1781_82_1 © NXP B.V. 2009. All rights reserved. Preliminary data sheet Rev. 01 — 13 February 2009 9 of 32 NXP Semiconductors TEA1781T; TEA1782T GreenChip PC secondary control ICs At any failure condition or as soon as the PS_OFF signal is high, the system switches to Protection / Standby mode. When a failure, such as a shorted or overloaded output, is detected, the system enters the Protection mode, disabling the main output circuits but leaving the standby output in operation. However, when, for example, a secondary FET is shorted, the system enters the System restart mode and switches off the primary side. When VDD is discharged below its minimum level, Vstop(VDD), the IC enters the Start-up mode and all switches are disabled. When the system is in Protection / Standby mode, the systems lowers its duty cycle and operating frequency to optimize the system’s efficiency. 7.4 Enable Normal mode In Standby mode, an optional PFC may be switched off. When switched to Normal mode, the system has a programmable delay before the main outputs (3.3 V, 5 V and 12 V) are switched on. During this delay the PFC can be activated. An extra safety feature has been built in when enabling Normal mode. If the input voltage is too low, which can occur when the PFC fails, the system stays in Standby mode. The input voltage is measured on a rectified secondary voltage, reflecting the input voltage; see Figure 7. In addition to a minimum input voltage, a delay can also be made to assure a proper start-up of the PFC before the system switches to Normal mode. A circuit according to Figure 8 must be built between the PS_ON# signal from the motherboard and the PS_OFF pin of the TEA1782T. Fig 7. Enable Normal mode assures a proper start-up of the forward converter Np / Ns VWND_SEC_2 Enable NM Digital control 1.25 V EN_NM 014aaa187 |
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