L6699D STMicroelectronics, L6699D Datasheet - Page 29

• 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
4.
5.
6.
Resonant converters work in capacitive mode when their switching frequency falls below a
critical value that depends on the loading conditions and the input-to-output voltage ratio.
They are especially prone to enter capacitive-mode when the input voltage is lower than the
minimum specified and/or the output is overloaded or short-circuited. Designing a converter
so that it never works in capacitive-mode, even under abnormal operating conditions, is
definitely possible but this may pose unacceptable design constraints in some cases.
To prevent the severe drawbacks of capacitive-mode operation, while enabling a design that
needs to ensure inductive-mode operation only in the specified operating range, neglecting
abnormal operating conditions, the L6699 provides the capacitive-mode detection function.
The IC monitors the phase relationship between the tank current circuit sensed on the ISEN
pin and the voltage applied to the tank circuit by the half bridge, checking that the former
lags behind the latter (inductive-mode operation). If the phase-shift approaches zero, which
is indicative of impending capacitive-mode operation, the monitoring circuit activates the
OCP procedure (see
frequency rise keeps the converter away from that dangerous condition. Also in this case
the DELAY pin is activated, so that the OLP function, if used, is eventually tripped after a
time T
If the phase relationship reverses abruptly (which may happen in case of dead short at the
converter's output), the L6699 is stopped immediately, the soft-start capacitor C
discharged and a new soft-start cycle is initiated after 50
the PFC_STOP pin is pulled low to stop the PFC stage as well.
When either MOSFET is turned on, the other one can be parasitically turned on too, if
the current injected through its Cgd and flowing through the gate driver's pull-down is
large enough to raise the gate voltage close to the turn-on threshold This would be a
lethal shoot-through condition for the half bridge leg.
The recovery of the body diodes generates large and energetic negative voltage spikes
because of the unavoidable parasitic inductance of the PCB subject to its di/dt. These
are coupled to the OUT pin and may damage the L6699.
There is a large common-mode EMI generation that adversely affects EMC.
SH
causing intermittent operation and reducing thermal stress.
Section 8: Current sensing, OCP and OLP
Doc ID 022835 Rev 2
Capacitive-mode detection function
µ
s idle time. During this idle period
) so that the resulting
SS
is totally
29/38