ssl1750 NXP Semiconductors, ssl1750 Datasheet - Page 17

• Manufacturer Part Number: ssl1750
• Description: Smps Control Ic For Led Drivers
• Manufacturer: NXP Semiconductors

NXP Semiconductors
SSL1750_1
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 pin VOSENSE reaches the V
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 12. Time-out protection
SoftStart
a. Circuit diagram
b. Timing diagram
=
3
V
TIMEOUT
FBCTRL
voltage
R
output
SS2
Rev. 01 — 15 September 2008
C
start(soft)(fb)
SS2
intended output
reached within
4.5 V
time-out time.
voltage not
2.5 V
is switched on as soon as V
start(fb)
3.5 V
restart
3 k
level and the voltage on pin FBSENSE has
SS2
30 A
and C
SMPS control IC for LED drivers
intended output voltage
reached within time-out
start(soft)(fb)
FBCTRL
SS2
CC
. See
time.
reaches V
Equation
4.5 V
2.5 V
014aaa049
R
014aaa050
SS2
SSL1750
© NXP B.V. 2008. All rights reserved.
startup
, with a
4.
. When the
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