tea1553t NXP Semiconductors, tea1553t Datasheet - Page 10

• Manufacturer Part Number: tea1553t
• Description: Tea1553t Greenchip Ii Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1553T_1
Product data sheet
7.8 Demagnetization
7.9 Overvoltage protection
The system will be in discontinuous conduction mode all the time. The oscillator will not
start a new primary stroke until the secondary stroke has ended.
Demagnetization features a cycle-by-cycle output short-circuit protection by immediately
lowering the frequency (longer off-time), thereby reducing the power level.
Demagnetization recognition is suppressed during the first t
suppression may be necessary in applications where the transformer has a large leakage
inductance and at low output voltages/start-up.
An OVP mode is implemented in the GreenChip series. For the TEA1553T, this works 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.
Pin OVPFCAP is used to program the OVP function as follows:
In the last case, the number of OVP events can be set by an external capacitor connected
to pin OVPFCAP:
Where n is the number of OVP counts which are allowed to occur before an actual OVP
state is detected.
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 could occur during ESD / lightning events.
If the output voltage exceeds the OVP trip level a few times, and then does not exceed it in
the next cycle, the internal counter will count down twice as fast as it counted up.
However, when typically 10 cycles of subsequent OVP events are detected, the IC
assumes a true OVP state exists and the OVP circuit switches the MOSFET off. Next, the
controller waits until the V
recharged to the V
Operation only recommences when the V
practice this only occurs when the mains input voltage has been disconnected for a short
period of time
The output voltage at which the OVP function trips, V
demagnetization resistor, R
C
1. Pin grounded: OVP is disabled.
2. Pin at 5 V (e.g. connected to pin 12, the VCC5V pin): the internal OVP circuit is
3. A capacitor is connected from the pin to the ground: this capacitor is used to set the
OVP
enabled.
number of OVP events that can occur before the logic determines that an actual OVP
condition exists. The minimum timing is the internal OVP timing.
=
n
I
--------------------------------------------------------------------- -
ch OVPFCAP
startup
V
OVPFCAP
Rev. 01 — 3 July 2007
level.
th(UVLO)
t
DEM
p OVPFCAP
:
level is reached on pin V
CC
voltage drops below a level of about 4.5 V, in
trip(OVPFCAP)
GreenChip II SMPS control IC
CC
sup(xfmr_ring)
, and then capacitor C
, can be set by the
TEA1553T
© NXP B.V. 2007. All rights reserved.
time. This
VCC
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