L6699DTR STMicroelectronics, L6699DTR Datasheet - Page 22

• Manufacturer Part Number: L6699DTR
• Description: AC/DC Switching Converters Enhanced High Volt Res CTRL 600V
• Manufacturer: STMicroelectronics

Specifications of L6699DTR

• Product Category: AC/DC Switching Converters

Operation at no load or very light load
22/38
Equation 6
Note that, unlike the f
some load Pout
transformer's peak currents are low enough not to cause audible noise.
The resonant converter's switching frequency, however, depends also on the input voltage;
so, in case there is quite a large input voltage range, with the circuit of
Pout
shown in
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
the total value R
(see
Figure 16. Load-dependent operating modes: timing diagram
Whichever circuit is in use, its operation can be described as follows. As the load falls below
the value Pout
voltage on the STBY pin (
outputs low, so that both MOSFETs of the half bridge leg are in the OFF-state. The voltage
V
it exceeds 1.29 V, the IC restarts switching. After a while,
response to the energy burst and stops the IC. In this way the converter works in a burst-
mode fashion with a nearly constant switching frequency. A further load decrease then
increases the time between consecutive bursts and/or reduces the duration of each burst.
This reduces the average switching frequency, which can go down even to few hundred
hertz. The timing diagram of
significant signals. 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, helps obtain
clean operation.
STBY
B
Section 10: Line sensing function
now increases as a result of the feedback reaction to the energy delivery stop and, as
would change considerably. In this case it is recommended to use the arrangement
Figure 15
B
A
B
the frequency tries to exceed the maximum programmed value f
A
/ (R
greater than the minimum one. Pout
+ R
, where the information on the converter's input voltage is added to the
A
max
B
+ R
much greater than R
considered in the
B
V
) needed to minimize the change in Pout
STBY
Figure 16
Doc ID 022835 Rev 2
) goes below 1.26 V. The IC then stops with both gate-drive
RF
).
max
illustrates this kind of operation, showing the most
=
Section 6.1: Oscillator
L
3
8
to minimize the effect on the LINE pin voltage
·
f
f
RF
max
min
min
-
B
1
is normally such that the
V
STBY
goes down again in
, here f
B
. Take care in choosing
Figure 14
max
is associated to
max
the value of
and the
L6699