L6699D STMicroelectronics, L6699D Datasheet - Page 15

• Manufacturer Part Number: L6699D
• Description: AC/DC Switching Converters Enhanced High Volt Res CTRL 600V
• Manufacturer: STMicroelectronics
• Type: High Voltage Controllersr

Specifications of L6699D

• Product Category: AC/DC Switching Converters
• Output Voltage: 13.3 V
• Input / Supply Voltage (max): 8.85 V
• Input / Supply Voltage (min): 16 V
• Switching Frequency: 235 kHz
• Supply Current: 3 mA
• Operating Temperature Range: - 25 C to + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SO-16
• Number Of Outputs: 1
• Output Current: 800 mA

L6699
6.2
Adaptive deadtime
A deadtime T
complementary one, where both switches are in the OFF-state, is essential to achieve soft-
switching. Its value must be larger than the time T
half bridge midpoint. This duration T
bridge midpoint, which must be completely charged or depleted and the value of the
resonant tank current during the transition.
With good approximation, the tank current during the transition time T
constant and equal to the “switched current” I
transition begins. If C
includes the Coss of the MOSFETs, the transformer's primary winding parasitic
capacitance, plus other stray contributors), the condition for soft-switching is:
Equation 3
which should be met under all operating conditions. This formula suggests that T
large enough to always exceed T
at a minimum and T
soft-switching too: in fact, the tank current must not change its sign within the deadtime,
which could lead to the turn-on of either MOSFET with a non-zero drain-to-source voltage
or, even worse, with the body diode of the other MOSFET conducting (capacitive mode
operation - see
occur at maximum load and minimum Vin, especially when the tank circuit is designed for a
low magnetizing current to optimize light load efficiency. Additionally, a too long deadtime
may increase conduction losses in the body diodes and significantly limit the operating
frequency of the half bridge.
A good approach is to automatically adjust T
operating conditions. This is the objective of the adaptive deadtime function in the L6699.
Figure 7
detector (the |d/dt| block) senses that the half bridge midpoint (connected to the OUT pin) is
swinging from B+ to GND or vice versa through the
the OUT pin (due to Cboot there is a DC voltage difference between them). The output of
the |d/dt| block is high as long as the OUT pin is swinging and, as the transition is
completed, the output goes low. A monostable circuit, sensitive to negative-going edges,
releases a pulse that marks the end of the deadtime.
and
Figure 8
D
inserted between the turn-off of either switch and the turn-on of the
Section 9: Capacitive-mode detection function
T
HB
at a maximum. However, a too long deadtime may lead to the loss of
show the principle schematic and its key waveforms. An edge
denotes the total parasitic capacitance of the half bridge midpoint (it
Doc ID 022835 Rev 2
T
, especially with maximum Vin and at no load, where I
T
T
T
depends on the total parasitic capacitance of the half
=
C
I
HB
S
D
S
, i.e. the value of the tank current as the
so that it tracks T
Vin
T
V
≤
needed for the rail-to-rail swing of the
BOOT
T
D
pin, which moves exactly following
for more details). This may
T
, keeping T
Application information
T
can be considered
T
≤ T
D
D
should be
under all
15/38
S
is