l6599atn STMicroelectronics, l6599atn Datasheet - Page 21

• Manufacturer Part Number: l6599atn
• Description: Improved High-voltage Resonant Controller
• Manufacturer: STMicroelectronics

L6599AT
The circuit shown in
series to C
operates like a capacitive current divider; C
is a low-loss type, and the sense resistor R
Equation 7
and C
If the resistor R
kΩ range), the circuit operates like a divider of the ripple voltage across the resonant
capacitor Cr, which, in turn, is related to its current through the reactance of Cr. Again, C
typically selected equal to Cr/100 or less, this time not necessarily a low-loss type, while R
(provided it is << R
Equation 8
where the reactance of C
I
Whichever circuit is used, the calculated values of Rs or R
preliminary values that may need to be adjusted after experimental verification.
OCP is effective in limiting primary-to-secondary energy flow in case of an overload or an
output short-circuit, but the output current through the secondary winding and rectifiers
under these conditions might be so high that they endanger the converter’s safety if
continuously flowing. To prevent any damage during these conditions it is customary to force
the intermittent operation of the converter, in order to bring the average output current to
values such that the thermal stress for the transformer and the rectifiers can be easily
handled.
With the L6599AT the designer can externally program the maximum time T
converter is allowed to run overloaded or under short-circuit conditions. Overloads or short-
circuits lasting less than T
immunity to short duration phenomena. If, instead, T
(OLP) procedure is activated that shuts down the L6599AT and, in cases of continuous
overload/short-circuit, results in continuous intermittent operation with a user-defined duty
cycle.
Crpk
= I
B
Crpkx
is such that R
A
. Again, C
is small (not above a few hundred ohms, just to limit current spiking) the circuit
A
in series with C
A
) according to:
Figure 11
B
B
·C
is such that R
B
A
SH
is in the range of 10 /f
(X
do not cause any other action, hence providing the system with
CA
b can be operated in two different ways. If the resistor R
Doc ID 15534 Rev 1
) and Cr (X
A
R
is not small (in this case it is typically selected in the ten
R
B
B
=
B
·C
=
I
0
Crpkx
I
8 .
B
0
Crpkx
A
8 .
B
Cr
is in the range of 10 /f
π
is typically selected equal to Cr/100 or less and
is selected as:
) should be calculated at the frequency where
π
⎛
⎜ ⎜
⎝
R
1
min
2
A
+
X
+
C
Cr
C
.
SH
X
A
r
2
C
⎞
⎟ ⎟
⎠
A
is exceeded an overload protection
B
should be considered
min
Application information
.
SH
that the
A
21/31
A
in
is
B