ssl1750 NXP Semiconductors, ssl1750 Datasheet - Page 11

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

NXP Semiconductors
SSL1750_1
Product data sheet
7.2.6 Burst mode control
When the output power of the flyback converter (see
converter switches over to frequency reduction mode. When frequency reduction mode is
entered by the flyback controller, the power factor correction circuit switches to burst mode
control.
In burst mode control, switching of the power factor correction circuit is inhibited until the
voltage on pin VOSENSE has dropped to V
to avoid audible noise (see
reaches V
soft-stop time the output voltage of the power factor correction circuit overshoots,
depending on the soft-start resistor and capacitor, R
the V
not reach the normal operation output voltage of the power factor correction circuit in a
typical application due to this overshoot.
The burst mode repetition rate is defined by the output power and the value of the bus
capacitor, C
During burst mode operation pin PFCCOMP is clamped between a voltage of 2.7 V (typ)
and 3.9 V (typ). The lower clamp voltage limits the maximum power that is delivered
during burst mode operation and yields a more sinusoidal input current during the burst
pulse. The upper clamp voltage ensures that the PFC can return to its normal regulation
point in a limited amount of time when returning from burst mode.
As soon as the flyback converter leaves frequency reduction mode, the power factor
correction circuit restores normal operation. To prevent continuous on and off switching of
the PFC circuit, a small hysteresis has been built in (50 mV (typ) on pin FBCTRL).
Fig 6.
burst(H)
Soft start-up and soft-stop of PFC
burst(H)
bus
voltage is well below the V
.
the soft-stop circuit is activated, again to avoid audible noise. During the
Rev. 01 — 15 September 2008
R SENSE1
S1
R SS1
C SS1
Section
11
PFCSENSE
I start(soft)PFC
7.2.5). As soon as the voltage on pin VOSENSE
reg(VOSENSE)
burst(L)
60 A
+
0.5 V
SOFT START
SOFT STOP
CONTROL
. Switching then restarts with a soft-start
voltage, the PFC output voltage does
OCP
SS1
Section
SMPS control IC for LED drivers
and C
7.3) is low, the flyback
014aaa018
SS1
on pin PFCSENSE. As
SSL1750
© NXP B.V. 2008. All rights reserved.
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