L6599A STMicroelectronics, L6599A Datasheet - Page 21

• Manufacturer Part Number: L6599A
• Description: IMPROVED HIGH-VOLTAGE RESONANT CONTROLLER
• Manufacturer: STMicroelectronics

Specifications of L6599A

• Two-level Ocp: frequency-shift and latched shutdown

L6599A
Figure 24. Burst-mode implementation:
Essentially, RF
enter burst-mode operation. Once fixed fmax, RF
Equation 3
Note that, unlike the f
f
the transformer's peak currents are low enough not to cause audible noise.
Resonant converter's switching frequency, however, depends also on the input voltage;
hence, in case there is quite a large input voltage range with the circuit of
value of Pout
arrangement shown in
added to the voltage applied to the STBY pin. Due to the strongly non-linear relationship
between switching frequency and input voltage, it is more practical to find empirically the
right amount of correction R
careful in choosing the total value R
the LINE pin voltage (see
Whichever circuit is in use, its operation can be described as follows. As the load falls below
the value Pout
the voltage on the STBY pin (V
gate-drive outputs low, so that both MOSFETs of the half-bridge leg are in OFF-state. The
voltage V
stop and, as it exceeds 1.29 V, the IC will restart switching. After a while, V
again in response to the energy burst and stop the IC. In this way the converter will work in a
burst-mode fashion with a nearly constant switching frequency. A further load decrease will
then cause a frequency reduction, which can go down even to few hundred hertz. The timing
diagram of
A small capacitor (typically in the hundred pF) from the STBY pin to ground, placed as close
to the IC as possible to reduce switching noise pick-up, will help get clean operation.
To help the designer meet energy saving requirements even in power-factor-corrected
systems, where a PFC pre-regulator precedes the DC-DC converter, the L6599A allows that
the PFC pre-regulator can be turned off during burst-mode operation, hence eliminating the
max
is associated to some load Pout
STBY
Figure 25
a) narrow input voltage range; b) wide input voltage range
B
B
will now increase as a result of the feedback reaction to the energy delivery
max
would change considerably. In this case it is recommended to use the
the frequency will try to exceed the maximum programmed value fmax and
will define the switching frequency fmax above which the L6599A will
max
illustrates this kind of operation, showing the most significant signals.
Figure 24
considered in the previous section (“
Section 7.6: Line sensing function
A
/ (R
Doc ID 15308 Rev 5
STBY
b, where the information on the converter's input voltage is
A
+ R
) will go below 1.24 V. The IC will then stop with both
A
B
RF
+ R
greater than the minimum one. Pout
B
max
) needed to minimize the change of Pout
B
much greater than R
=
3
8
f
f
RF
max
min
max
min
−
will be found from the relationship:
1
).
Section 7.1: Oscillator
C
to minimize the effect on
Application information
B
STBY
Figure 24
will be such that
will go down
B
. Just be
a the
“), here
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