L6699D STMicroelectronics, L6699D Datasheet - Page 28

• 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

Capacitive-mode detection function
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Capacitive-mode detection function
Normally, the resonant half bridge converter operates with the resonant tank current lagging
behind the square-wave voltage applied by the half bridge leg, like a circuit having a
reactance of an inductive nature. In this way the applied voltage and the resonant current
have the same sign at every transition of the half bridge, which is a necessary condition in
order for soft-switching to occur (zero-voltage switching, ZVS at turn-on for both MOSFETs).
Therefore, should the phase relationship reverse, i.e. the resonant tank current anticipates
the applied voltage, like in circuits having a capacitive reactance, soft-switching would be
lost. This is termed capacitive-mode operation and must be avoided because of its
significant drawbacks:
1.
2.
3.
Figure 21. Details of hard-switching transition during capacitive-mode operation
Both MOSFETs feature hard-switching at turn-on, like in conventional PWM-controlled
converters (see
higher than the total power normally dissipated under “soft-switching” conditions and
this may easily lead to their overheating, since heatsinking is not usually sized to
handle this abnormal condition.
The body diode of the MOSFET just switched off conducts current during deadtime and
its voltage is abruptly reversed by the other MOSFET turned on (see
Therefore, once reverse-biased, the conducting body diode keeps its low impedance
until it recovers, therefore creating a condition equivalent to a shoot-through of the half
bridge leg. This is a potentially destructive condition (see next point) and causes
additional power dissipation due to the current and voltage of the conducting body
diode simultaneously high during part of its recovery.
There is an extremely high reverse dv/dt (many tens of V/ns!) experienced by the
conducting body diode at the end of its recovery with the other MOSFET turned on.
This dv/dt may exceed the rating of the MOSFET and lead to an immediate failure
because of the second breakdown of the parasitic BJT intrinsic in its structure. If a
MOSFET is hot, the turn-on threshold of its parasitic BJT is lower, and dv/dt-induced
failure is much more likely. The L6699 may be also damaged if its OUT pin is subject to
a dv/dt exceeding the AMR (50 V/ns).
Figure 21
Doc ID 022835 Rev 2
). The associated capacitive losses may be considerably
Figure 21
).
L6699