Tuesday, January 10, 2017

LG Power supply Schematic - 715T3181 - LG 26LG3000 – Using ICs - L6599D – FAN7529

L6599D Resonant controller
The L6599 is a double-ended controller specific for the resonant half-bridge topology. It provides 50 % complementary duty cycle: the high-side switch and the low-side switch are driven ON\OFF 180 degree out-of-phase for exactly the same time. Output voltage regulation is obtained by modulating the operating frequency. A fixed deadtime inserted between the turn-OFF of one switch and the turn-ON of the other one guarantees soft-switching and enables high-frequency operation.
To drive the high-side switch with the bootstrap approach, the IC incorporates a high-voltage floating structure able to withstand more than 600 V with a synchronous-driven high-voltage DMOS that replaces the external fast-recovery bootstrap diode.
At start-up, to prevent uncontrolled inrush current, the switching frequency starts from a programmable maximum value and progressively decays until it reaches the steady-state value determined by the control loop. This frequency shift is non linear to minimize output voltage overshoots; its duration is programmable as well.
Pin functions
PIN NO
Name
Function
1
CSS
Soft start. This pin connects an external capacitor to GND and a resistor to RFmin (pin 4)
that set both the maximum oscillator frequency and the time constant for the frequency shift
that occurs as the chip starts up (soft-start). An internal switch discharges this capacitor
every time the chip turns OFF (VCC < UVLO, LINE < 1.25 V or > 6 V, DIS > 1.85 V, ISEN >
1.5 V, DELAY > 3.5 V) to make sure it will be soft-started next, and when the voltage on the
current sense pin (ISEN) exceeds 0.8V, as long as it stays above 0.75 V.
2
DELAY
Delayed shutdown upon overcurrent. A capacitor and a resistor are connected from this pin
to GND to set both the maximum duration of an overcurrent condition before the IC stops
switching and the delay after which the IC restarts switching. Every time the voltage on the
ISEN pin exceeds 0.8 V the capacitor is charged by an internal 150µA current generator and
is slowly discharged by the external resistor. If the voltage on the pin reaches 2 V, the soft
start capacitor is completely discharged so that the switching frequency is pushed to its
maximum value and the 150 µA is kept always on. As the voltage on the pin exceeds 3.5 V
the IC stops switching and the internal generator is turned OFF, so that the voltage on the
pin will decay because of the external resistor. The IC will be soft-restarted as the voltage
drops below 0.3V. In this way, under short circuit conditions, the converter will work
intermittently with very low input average power.
3
CF
Timing capacitor. A capacitor connected from this pin to GND is charged and discharged by
internal current generators programmed by the external network connected to pin 4 (RFmin)
and determines the switching frequency of the converter.

4
RFmin
Minimum oscillator frequency setting. This pin provides a precise 2 V reference and a
resistor connected from this pin to GND defines a current that is used to set the minimum
oscillator frequency. To close the feedback loop that regulates the converter output voltage
by modulating the oscillator frequency, the phototransistor of an optocoupler will be
connected to this pin through a resistor. The value of this resistor will set the maximum
operating frequency. An R-C series connected from this pin to GND sets frequency shift at
start-up to prevent excessive energy inrush (soft-start).
5
STBY
Burst-mode operation threshold. The pin senses some voltage related to the feedback
control, which is compared to an internal reference (1.25 V). If the voltage on the pin is lower
than the reference, the IC enters an idle state and its quiescent current is reduced. The chip
restarts switching as the voltage exceeds the reference by 50 mV. Soft-start is not invoked.
This function realizes burst-mode operation when the load falls below a level that can be
programmed by properly choosing the resistor connecting the optocoupler to pin RFmin (see
block diagram). Tie the pin to RFmin if burst-mode is not used.
6
ISEN
Current sense input. The pin senses the primary current though a sense resistor or a
capacitive divider for lossless sensing. This input is not intended for a cycle-by-cycle control;
hence the voltage signal must be filtered to get average current information. As the voltage
exceeds a 0.8 V threshold (with 50 mV hysteresis), the soft-start capacitor connected to pin
1 is internally discharged: the frequency increases hence limiting the power throughput.
Under output short circuit, this normally results in a nearly constant peak primary current.
This condition is allowed for a maximum time set at pin 2. If the current keeps on building up
despite this frequency increase, a second comparator referenced at 1.5 V latches the device
off and brings its consumption almost to a “before start-up” level. The information is latched
and it is necessary to recycle the supply voltage of the IC to enable it to restart: the latch is
removed as the voltage on the Vcc pin goes below the UVLO threshold. Tie the pin to GND if
the function is not used.
7
LINE
Line sensing input. The pin is to be connected to the high-voltage input bus with a resistor
divider to perform either AC or DC (in systems with PFC) brownout protection. A voltage
below 1.25 V shuts down (not latched) the IC, lowers its consumption and discharges the
soft-start capacitor. IC’s operation is re-enabled (soft-started) as the voltage exceeds 1.25 V.
The comparator is provided with current hysteresis: an internal 15 µA current generator is
ON as long as the voltage applied at the pin is below 1.25 V and is OFF if this value is
exceeded. Bypass the pin with a capacitor to GND to reduce noise pick-up. The voltage on
the pin is top-limited by an internal zener. Activating the zener causes the IC to shut down
(not latched). Bias the pin between 1.25 and 6 V if the function is not used.
8
DIS
Latched device shutdown. Internally the pin connects a comparator that, when the voltage
on the pin exceeds 1.85 V, shuts the IC down and brings its consumption almost to a “before
start-up” level. The information is latched and it is necessary to recycle the supply voltage of
the IC to enable it to restart: the latch is removed as the voltage on the VCC pin goes below
the UVLO threshold. Tie the pin to GND if the function is not used.
9
PFC_STOP
Open-drain ON/OFF control of PFC controller. This pin, normally open, is intended for
stopping the PFC controller, for protection purpose or during burst-mode operation. It goes
low when the IC is shut down by DIS > 1.85 V, ISEN > 1.5 V, LINE > 6 V and STBY < 1.25 V.
The pin is pulled low also when the voltage on pin DELAY exceeds 2V and goes back open
as the voltage falls below 0.3V. During UVLO, it is open. Leave the pin unconnected if not
used.
10
GND
Chip ground. Current return for both the low-side gate-drive current and the bias current of
the IC. All of the ground connections of the bias components should be tied to a track going
to this pin and kept separate from any pulsed current return.

11
LVG
Low-side gate-drive output. The driver is capable of 0.3 A min. source and 0.8 A min. sink
peak current to drive the lower MOSFET of the half-bridge leg. The pin is actively pulled to
GND during UVLO.
12
VCC
Supply Voltage of both the signal part of the IC and the low-side gate driver. Sometimes a
small bypass capacitor (0.1 µF typ.) to GND might be useful to get a clean bias voltage for
the signal part of the IC.
13
N.C.
High-voltage spacer. The pin is not internally connected to isolate the high-voltage pin and
ease compliance with safety regulations (creepage distance) on the PCB.
14
OUT
High-side gate-drive floating ground. Current return for the high-side gate-drive current.
Layout carefully the connection of this pin to avoid too large spikes below ground.
15
HVG
High-side floating gate-drive output. The driver is capable of 0.3 A min. source and 0.8A min.
sink peak current to drive the upper MOSFET of the half-bridge leg. A resistor internally
connected to pin 14 (OUT) ensures that the pin is not floating during UVLO.
16
VBOOT
High-side gate-drive floating supply Voltage. The bootstrap capacitor connected between
this pin and pin 14 (OUT) is fed by an internal synchronous bootstrap diode driven in-phase
with the low-side gate-drive. This patented structure replaces the normally used external
diode
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