tea1533p NXP Semiconductors, tea1533p Datasheet - Page 8

• Manufacturer Part Number: tea1533p
• Description: Greenchip Smps Control Ic
• Manufacturer: NXP Semiconductors

Philips Semiconductors
OverVoltage Protection (OVP)
An OVP mode is implemented in the GreenChip series.
This works for the TEA1533 by sensing the auxiliary
voltage via the current flowing into pin DEM during the
secondary stroke. The auxiliary winding voltage is a
well-defined replica of the output voltage. Any voltage
spikes are averaged by an internal filter.
If the output voltage exceeds the OVP trip level, an internal
counter starts counting subsequent OVP events. The
counter has been added to prevent incorrect OVP
detections which might occur during ESD or lightning
events. If the output voltage exceeds the OVP trip level a
few times and not again in a subsequent cycle, the internal
counter will count down with twice the speed compared
with counting-up. However, when typical 10 cycles of
subsequent OVP events are detected, the IC assumes a
true OVP and the OVP circuit switches the power
MOSFET off. Next, the controller waits until the UVLO
level is reached on pin V
capacitor C
Regarding the TEA1533P, this IC will not start switching
again. Subsequently, V
level, etc. Operation only recommences when the V
voltage drops below a level of approximately 4.5 V
(practically when V
period).
Regarding the TEA1533AP, switching starts again (safe
restart mode) when the V
process is repeated as long as the OVP condition exists.
The output voltage V
can be set by the demagnetization resistor, R
where N
number of auxiliary turns of the transformer.
Current I
The value of R
transformer, thus making an accurate OVP possible.
2002 Aug 23
V
----------- I
N
N
o OVP
aux
GreenChip
s
(OVP)(DEM)
s
(OVP)(DEM)
=
is the number of secondary turns and N
VCC
DEM
will be recharged to the V
mains
can be adjusted to the turns ratio of the
TM
R
is internally trimmed.
o(OVP)
DEM
II SMPS control IC
CC
has been disconnected for a short
CC
+
start
will drop again to the UVLO
at which the OVP function trips,
. When V
V
clamp(DEM)(pos)
level is reached. This
CC
drops to UVLO,
start
level.
DEM
aux
:
CC
is the
8
Valley switching
A new cycle starts when the power MOSFET is switched
on (see Fig.8). After the ‘on-time’ (which is determined by
the ‘sense’ voltage and the internal control voltage), the
switch is opened and the secondary stroke starts. After the
secondary stroke, the drain voltage shows an oscillation
with a frequency of approximately
where L
and C
As soon as the oscillator voltage is high again and the
secondary stroke has ended, the circuit waits for the
lowest drain voltage before starting a new primary stroke.
This method is called valley detection. Figure 8 shows the
drain voltage together with the valley signal, the signal
indicating the secondary stroke and the oscillator signal.
In an optimum design, the reflected secondary voltage on
the primary side will force the drain voltage to zero. Thus,
zero voltage switching is very possible, preventing large
capacitive switching losses
allowing high frequency operation, which results in small
and cost effective inductors.
d
is the capacitance on the drain node.
p
is the primary self inductance of the transformer
TEA1533P; TEA1533AP
P
=
1
-- -
2
---------------------------------------------- -
2
Product specification
C V
2
1
L
p
f
and
C
d