tea1781 NXP Semiconductors, tea1781 Datasheet - Page 8

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

NXP Semiconductors
TEA1781_82_1
Preliminary data sheet
7.3 Mode of operation
The VDD capacitor is charged and regulated to the V
the TEA1781T. This VDD voltage is the supply voltage for both secondary ICs.
Once the VDD voltage reaches the V
5 V standby is started up via a so-called soft start. This implies that during a certain time,
t
system is started up, the VDD voltage is taken over by an auxiliary winding of the
5 V standby output, as shown in
during standby and normal operation.
As the secondary ICs are supplied via the TEA1781T and measured in the TEA1782T,
both ICs are disabled in case of an open connection in the supply chain.
If the VDD voltage drops below its V
by actively turning off all switches. This avoids undefined conditions resulting from
charged gate capacitances.
After the system has started up, the TEA1782T defines the mode of operation. It features
four operation modes: Start-up mode, Protection/Standby mode, Normal mode and
System restart mode, as depicted in
When the VDD voltage is below its stop level, the TEA1782T enters the Start-up mode
and the TEA1781T charges the VDD capacitors to V
has charged the VDD capacitor above V
Protection/Standby mode and the 5 V standby output slowly rises from zero to its required
value.
When the PS_OFF signal becomes active low, the system switches to Normal mode
enabling the main outputs (3.3 V, 5 V, 12 V and 12 V). The 12 V (and 12 V) output is
regulated by the TEA1782T itself, whereas the 3.3 V and 5 V output are regulated by the
TEA1781T. The TEA1781T activates the 3.3 V and 5 V outputs via the ENABLE signal.
start(soft)
Fig 6.
, the output voltage slowly ramps up from zero to the required value. Once the
State diagram TEA1771T
Rev. 01 — 13 February 2009
V
V
VDD
ENABLE
NORMAL
+ PS_OFF+ PROT_12V + UVP_STB
< V
I
ENABLE
stop(VDD)
= 11 V
Figure
> I
stop(VDD)
Figure
startup(VDD)
prot(ENABLE)
PS_OFF
V
Digital control
5. This ensures an efficient 12 V VDD voltage
ENABLE
STARTUP
RESTART
startup(VDD)
SYSTEM
TEA1781T; TEA1782T
6.
level, the system disables all output voltages
= 4 V
+ EN_NM
level, measured in the TEA1782T, the
GreenChip PC secondary control ICs
, the TEA1782T jumps into
V
PROT/STDB
V
ENABLE
reg(VDD)
VDD
reg(VDD)
> V
system failure
detection
= 4 V
startup(VDD)
via the start-up pin. When it
level via a linear regulator in
014aaa186
© NXP B.V. 2009. All rights reserved.
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