TEA1750 NXP Semiconductors, TEA1750 Datasheet - Page 16

• Manufacturer Part Number: TEA1750
• Description: GreenChip III SMPS control IC
• Manufacturer: NXP Semiconductors

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NXP Semiconductors
TEA1750_2
Product data sheet
7.3.6 Soft start-up (pin FBSENSE)
To prevent audible transformer noise during start-up, the transformer peak current, I
slowly increased by the soft start function. This can be achieved by inserting a resistor
and a capacitor between pin FBSENSE and the current sense resistor.
An internal current source charges the capacitor to V = I
maximum of approximately 0.5 V.
The start level and the time constant of the increasing primary current level can be
adjusted externally by changing the values of R
The soft start current I
voltage on the VOSENSE pin reaches the V
has reached 0.5 V, the flyback converter starts switching.
The soft start current flows as long as the voltage on pin FBSENSE is below
approximately 0.5 V. If the voltage on pin FBSENSE exceeds 0.5 V, the soft start current
source starts limiting the current. After the flyback converter has started, the soft start
current source is switched off.
Fig 11. Time-out protection
SoftStart
a. Circuit diagram
b. Timing diagram
=
3
V
TIMEOUT
FBCTRL
voltage
output
R
SS2
Rev. 02 — 15 December 2008
start(soft)(fb)
C
SS2
intended output
reached within
4.5 V
time-out time.
voltage not
2.5 V
is switched on as soon as V
3.5 V
start(fb)
3 k
restart
SS2
30 A
level and the voltage on pin FBSENSE
and C
intended output voltage
reached within time-out
start(soft)(fb)
FBCTRL
GreenChip III SMPS control IC
SS2
CC
.
time.
reaches V
x R
4.5 V
2.5 V
014aaa049
014aaa050
SS2
TEA1750
© NXP B.V. 2008. All rights reserved.
startup
, with a
. When the
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