L6599 STMicroelectronics, L6599 Datasheet - Page 18

• Manufacturer Part Number: L6599
• Description: High-voltage resonant controller
• Manufacturer: STMicroelectronics

Specifications of L6599

• Dimensions (l/w/h): 132 mm / 52 mm / 22 mm
• Universal Ac Mains Range: 90 VAC to 264 VAC
• High Output Power: 90 W (4.74 A, 19 VDC)
• Very Low Output Noise And Ripple: less than 300 m VP-P
• Very Low Standby Power: less than 0.5 W at 264 V
• Hiccup Mode: Auto recovery with SCP
• Latch Mode: OVP acts while VOUT > 29 VDC

Application information
7.2
18/36
Operation at no load or very light load
When the resonant half-bridge is lightly loaded or unloaded at all, its switching frequency will
be at its maximum value. To keep the output voltage under control in these conditions and to
avoid losing soft-switching, there must be some significant residual current flowing through
the transformer's magnetizing inductance. This current, however, produces some
associated losses that prevent converter's no-load consumption from achieving very low
values.
To overcome this issue, the L6599 enables the designer to make the converter operate
intermittently (burst-mode operation), with a series of a few switching cycles spaced out by
long idle periods where both MOSFETs are in OFF-state, so that the average switching
frequency can be substantially reduced. As a result, the average value of the residual
magnetizing current and the associated losses will be considerably cut down, thus
facilitating the converter to comply with energy saving recommendations.
The device can be operated in burst-mode by using pin 5 (STBY): if the voltage applied to
this pin falls below 1.25 V the IC will enter an idle state where both gate-drive outputs are
low, the oscillator is stopped, the soft-start capacitor C
reference at RF
discharge. The IC will resume normal operation as the voltage on the pin exceeds 1.25 V by
50 mV.
To implement burst-mode operation the voltage applied to the STBY pin needs to be related
to the feedback loop.
input voltage range (e.g. when there is a PFC front-end).
Figure 24. Burst-mode implementation: narrow input voltage range
Figure 25. Burst-mode implementation: wide input voltage range
L6599
min
R
pin stays alive to minimize IC's consumption and V
Fmin
R
Fmin
Figure 24
R
Fmax
R
Fmax
shows the simplest implementation, suitable with a narrow
R
A
RFmin
STBY
RFmin
STBY
4
5
4
5
L6599
L6599
SS
R
keeps its charge and only the 2 V
B
R
A
+ R
7
B
>> R
LINE
C
CC
B+
R
Fmin
capacitor's
R
R
RC
RD
D
C
R
Fmax
L6599