L6599 STMicroelectronics, L6599 Datasheet - Page 24

• 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
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Figure 31. Lossless current sensing technique, with capacitive shunt
pk
The device is equipped with a current sensing input (pin 6, ISEN) and a sophisticated
overcurrent management system. The ISEN pin is internally connected to the input of a first
comparator, referenced to 0.8 V, and to that of a second comparator referenced to 1.5 V. If
the voltage externally applied to the pin by either circuit in
0.8 V the first comparator is tripped and this causes an internal switch to be turned on and
discharge the soft-start capacitor C
increase the oscillator frequency and thereby limit energy transfer. The discharge will go on
until the voltage on the ISEN pin has dropped by 50 mV; this, with an averaging time in the
range of 10/f
operation results in a nearly constant peak primary current.
It is normal that the voltage on the ISEN pin may overshoot above 0.8 V; however, if the
voltage on the ISEN pin reaches 1.5 V, the second comparator will be triggered, the L6599
will shutdown and latch off with both the gate-drive outputs and the PFC_STOP pin low,
hence turning off the entire unit. The supply voltage of the IC must be pulled below the
UVLO threshold and then again above the start-up level in order to restart. Such an event
may occur if the soft-start capacitor C
or in case of transformer's magnetizing inductance saturation or a shorted secondary
rectifier.
In the circuit shown in
low-side MOSFET is used, note the particular connection of the resonant capacitor. In this
way the voltage across R
and is positive most of the switching period, except for the time needed for the resonant
current to reverse after the low-side MOSFET has been switched OFF. Assuming that the
time constant of the RC filter is at least ten times the minimum switching frequency f
approximate value of R
where I
and the primary winding of the transformer, which is related to the maximum load and the
minimum input voltage.
Crpkx
min
is the maximum desired peak current flowing through the resonant capacitor
, ensures an effective frequency rise. Under output short circuit, this
L6599
Figure 30
S
can be found using the empirical equation:
S
6
is related to the current flowing through the high-side MOSFET
ISEN
C
B
τ
where a sense resistor R
R
≈
S
f
10
min
SS
=
1N4148
R
SS
B
(see
Vs
-------------- -
I
Crpkx
is too large, so that its discharge is not fast enough
pkx
Chapter 7.3:
1N4148
≈
C
5 0.8
--------------- -
I
A
Crpkx
⋅
R
A
≈
-------------- -
I
Crpkx
I
Cr
4
Soft-start). This will quickly
S
Figure 30
in series to the source of the
Cr
or
Figure 31
V
Crpk
exceeds
min
L6599
, the