tea1781 NXP Semiconductors, tea1781 Datasheet - Page 6

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

NXP Semiconductors
7. Functional description
TEA1781_82_1
Preliminary data sheet
7.1 Introduction
Table 3.
A PC power supply has to supply a number of different supply voltages: 12 V, 5 V, 3.3 V,
today require dissipative post regulations.
Because the system must be able to switch off the main supplies (12 V, 5 V, 3.3 V, 12 V)
in Standby mode but keep the 5 V standby in operation, a separate standby supply is still
common practice.
With the GreenChip PC chip set (TEA1771T, TEA1781T, TEA1782T) a system
configuration is introduced that integrates the post regulation and combines the main and
standby converter into a single system. This high level of integration reduces the total cost
of the system.
Because the output voltages are regulated separately, it makes the design of the
converter easier as none of the output voltages is directly related to the number of turns
on the transformer.
One of the main differences of this topology compared to commonly used solutions is the
use of switches instead of Schottky diodes, although the rectifying switch is a so-called
bidirectional switch. This switch is built up by two standard FETs in anti-series.
Symbol
PS_OFF
ENABLE
PGND_12V
GSF_12V
GND
GND
VDD
GSF_STB
PGND_STB
PGOOD
OPTO
VOUT_STB
CS_STB
OCP_STB
DF_STB
GSB_STB
FSB_STB
WND_SEC_1
GSR
FSR
12 V and 5 V standby. To achieve the required output voltage accuracy, the systems of
TEA1782T Pin description
Pin
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Rev. 01 — 13 February 2009
Description
power supply off (via delay network connected to PS_ON#)
enabling Normal mode
power ground 12 V output
gate driver switch SF_12V
ground
ground
supply voltage
gate driver switch SF_stb
power ground standby output
PowerGood (delay setting for power OK)
opto coupler
output voltage standby output
current sense standby output
overcurrent protection standby output
drain voltage of switch SF_stb
gate driver switch SB_stb
gate driver switch SB_stb
secondary transformer 12 V / standby winding voltage
gate driver switch SR (12 V)
floating supply switch SR (12 V)
…continued
TEA1781T; TEA1782T
GreenChip PC secondary control ICs
© NXP B.V. 2009. All rights reserved.
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