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L6699 Schematic ( PDF Datasheet ) - STMicroelectronics
| Teilenummer | L6699 |
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| Beschreibung | Enhanced high voltage resonant controller | |
| Hersteller | STMicroelectronics | |
| Logo |  |
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Gesamt 30 Seiten 
L6699
Enhanced high voltage resonant controller
Features
■ Symmetrical duty cycle, variable frequency
control of resonant half bridge
■ Self-adjusting adaptive deadtime
■ High-accuracy oscillator
■ 2-level OCP: frequency-shift and immediate
shutdown
■ Interface with PFC controller
■ Anti-capacitive-mode protection
■ Burst-mode operation at light load
■ Input for brownout protection or power-on/off
sequencing
■ “Safe-start” procedure prevents hard switching
at startup
■ 600 V rail compatible high-side gate driver with
integrated bootstrap diode and high dv/dt
immunity
■ -300/800 mA high-side and low-side gate
drivers with UVLO pull-down
■ SO16N package
Datasheet − production data
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Applications
■ SMPS for LCD TVs, desktop and AIO PCs,
servers, Telecom power
■ AC-DC adapter, open frame SMPS
Table 1. Device summary
Order codes
Package
L6699D
L6699DTR
SO16N
Packing
Tube
Tape and reel
Figure 1. Block diagram
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January 2013
This is information on a product in full production.
Doc ID 022835 Rev 2
1/38
www.st.com
38
 
Pin connections
4 Pin connections
L6699
Figure 2. Pin connections (top view)
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Table 4. Pin functions
N. Name
Function
Soft-start. This pin connects an external capacitor to GND and a resistor to
RFmin (pin 4) that set both the initial oscillator frequency and the time constant
for the frequency shift that occurs as the chip starts up (soft-start). An internal
1
CSS
switch discharges this capacitor every time the chip turns off (VCC < UVLO,
LINE < 1.25 V, DIS > 1.85 V, ISEN > 1.5 V, DELAY > 2 V) to make sure it is soft-
started next. Additionally the switch is activated when the voltage on the current
sense pin (ISEN) exceeds 0.8 V or when the converter is working too close to,
or in, the capacitive-mode operation.
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 350 µA current pulses and is slowly discharged by the external
resistor. If the voltage on the DELAY pin reaches 2 V, the soft-start capacitor is
completely discharged so that the switching frequency is pushed to its
maximum value and the 350 µA current source is kept always on. As the
voltage on the DELAY pin exceeds 3.5 V the IC stops switching and the internal
2 DELAY generator is turned off, so that the voltage on the pin decays because of the
external resistor. The IC is soft-restarted as the voltage drops below 0.3 V. In
this way, under short-circuit conditions, the converter works intermittently with
very low input average power.
If the voltage on the ISEN pin exceeds 1.5 V, the L6699 is immediately stopped
and the 350 µA current source is kept on until the voltage on the DELAY pin
reaches 3.5 V. Then, the generator is turned off and the voltage on the pin
decays because of the external resistor. Also in this case the IC is soft-restarted
as the voltage drops below 0.3 V.
Timing capacitor. A capacitor connected from this pin to GND is charged and
3
CF
discharged by internal current generators programmed by the external network
connected to pin 4 (RFmin) and determines the switching frequency of the
converter.
6/38 Doc ID 022835 Rev 2
6 Page 
Application information
6 Application information
L6699
The L6699 is an advanced double-ended controller specific to resonant half bridge topology.
In these converters the MOSFETs of the half bridge leg are alternately switched on and off
(180° out-of-phase) for exactly the same time. This is commonly referred to as symmetrical
operation at “50% duty cycle”, although the real duty cycle, i.e. the ratio of the ON-time of
either switch to the switching period, is actually less than 50%. The reason is that there is a
deadtime TD inserted between the turn-off of either MOSFET and the turn-on of the other
one, where both MOSFETs are off. This deadtime is essential in order for the converter to
work correctly: it enables soft-switching and, then, high-frequency operation with high
efficiency and low EMI emissions.
A special feature of this IC is that it is able to automatically adjust TD within a range so that it
best fits the transition times of the half bridge midpoint (adaptive deadtime). This allows the
user to optimize the design of the resonant tank so that soft-switching can be achieved with
a lower level of reactive energy (i.e. magnetizing current), therefore optimizing efficiency
under a broader load range, from full to light load.
To perform converter output voltage regulation the device is able to operate in different
modes (Figure 1), depending on the load conditions:
1. Variable frequency at heavy and medium/light load. A relaxation oscillator (see
Section 6.1: Oscillator for more details) generates a symmetrical triangular waveform,
which MOSFET switching is locked to. The frequency of this waveform is related to a
current that is modulated by the feedback circuitry. As a result, the tank circuit driven by
the half bridge is stimulated at a frequency dictated by the feedback loop to keep the
output voltage regulated, therefore exploiting its frequency-dependent transfer
characteristics.
2. Burst-mode control with no or very light load. When the load falls below a value, the
converter enters a controlled intermittent operation, where a series of a few switching
cycles at a nearly fixed frequency are spaced out by long idle periods where both
MOSFETs are in the OFF-state. A further load decrease is translated into longer idle
periods and then in a reduction of the average switching frequency. When the converter
is completely unloaded, the average switching frequency can go down even to few
hundred hertz, therefore minimizing magnetizing current losses as well as all
frequency-related losses and making it easier to comply with energy saving
specifications.
Figure 4. Multimode operation of the L6699
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12/38
Doc ID 022835 Rev 2
12 Page | ||
| Seiten | Gesamt 30 Seiten | |
| PDF Download | [ L6699 Schematic.PDF ] | |
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