tea1781 NXP Semiconductors, tea1781 Datasheet - Page 9

• Manufacturer Part Number: tea1781
• Description: Greenchip Pc Secondary Control Ics
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1781_82_1
Preliminary data sheet
7.4 Enable Normal mode
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, V
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.
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
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
PS_OFF pin of the TEA1782T.
Fig 7.
must be built between the PS_ON# signal from the motherboard and the
Enable Normal mode assures a proper start-up of the forward converter
Figure
7.
Np / Ns
Rev. 01 — 13 February 2009
V
WND_SEC_2
1.25 V
TEA1781T; TEA1782T
Enable NM
GreenChip PC secondary control ICs
stop(VDD)
EN_NM
Digital control
, the IC enters the Start-up
014aaa187
© NXP B.V. 2009. All rights reserved.
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