ssl1750 NXP Semiconductors, ssl1750 Datasheet - Page 16

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

NXP Semiconductors
SSL1750_1
Product data sheet
7.3.4 Demagnetization (pin FBAUX)
7.3.5 Flyback control / time-out (pin FBCTRL)
The driver output is latched in the logic, preventing multiple switch-on.
The system is always in quasi-resonant or discontinuous conduction mode. The internal
oscillator does not start a new primary stroke until the previous secondary stroke has
ended.
Demagnetization features a cycle-by-cycle output short circuit protection by immediately
lowering the frequency (longer off-time), thereby reducing the power level.
Demagnetization recognition is suppressed during the first t
This suppression may be necessary at low output voltages and at start-up and in
applications where the transformer has a large leakage inductance.
If pin FBAUX is open-circuit or not connected, a fault condition is assumed and the
converter stops operating immediately. Operation restarts as soon as the fault condition is
removed.
Pin FBCTRL is connected to an internal voltage source of 3.5 V via an internal resistor
(typical resistance is 3 k ). As soon as the voltage on this pin is above 2.5 V (typ), this
connection is disabled. Above 2.5 V the pin is biased with a small current. When the
voltage on this pin rises above 4.5 V (typ), a fault is assumed and switching is inhibited.
When a small capacitor is connected to this pin, a time-out function can be created to
protect against an open control loop situation (see
function can be disabled by connecting a resistor (100 k ) to ground on pin FBCTRL.
If the pin is shorted to ground, switching of the flyback controller is inhibited.
In normal operating conditions, when the converter is regulating the output, the voltage on
pin FBCTRL is between 1.4 V and 2.0 V (typical values) from minimum to maximum
output power.
Fig 11. Frequency control of flyback part
FBSENSE peak voltage
V
sense(fb)max
Rev. 01 — 15 September 2008
0.52 V
0.13 V
PFC burst mode
cycle skip
flyback
mode
flyback
frequency
reduction
1.4 V
1.5 V
PFC on
Figure 12
2.0 V
discontinuous
SMPS control IC for LED drivers
flyback
or QR
V
FBCTRL
sup(xfmr_ring)
and
014aaa028
Figure
SSL1750
© NXP B.V. 2008. All rights reserved.
time (2 s typ).
13). The time-out
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