TEA1552 View Datasheet(PDF) - Philips Electronics
Part Name
Description
View to exact match
TEA1552 Datasheet PDF : 24 Pages
| |||
Philips Semiconductors
GreenChip™II SMPS control IC
Product specification
TEA1552
handbook, full pagewidth
1.5 V − VCTRL current
comparator
CTRL
DRIVER
DRIVER
VCC(5V)
X2
Isense
VCOadj
5 V Vx
V
I
OSCILLATOR
fosc
dV2
fmax
fmin
VSTDBY
(V)
5
0
cycle
skipping
dV1
dV3
dV4
Vx (mV)
VCOadj
Vx (mV)
1
MBL502
0
The voltage levels dV1, dV2, dV3 and dV4 are fixed in the IC to typically 50 mV, 18 mV, 40 mV and 15 mV respectively.
The level at which VCO mode of operation starts or ends can be externally controlled with the VCOadj pin.
Fig.7 A functional implementation of the standby and cycle skipping circuitry.
Vx (mV)
Standby output
The STDBY output pin (VSTDBY = 5 V) can be used to drive
an external NPN transistor or FET in order to e.g.
switch-off a PFC circuit. The STDBY output is activated by
the internal VCO: as soon as the VCO has reduced the
switching frequency to (almost) the minimum frequency of
25 kHz, the STDBY output will be activated (see Fig.7).
The STDBY output will go low again as soon as the VCO
allows a switching frequency close to the maximum
frequency of 125 kHz.
Demagnetization
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
time (tsuppr). This suppression may be necessary in
applications where the transformer has a large leakage
inductance and at low output voltages/start-up.
OverVoltage Protection (OVP)
An OVP mode is implemented in the GreenChip series.
For the TEA1552, 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.
If the output voltage exceeds the OVP trip level, the OVP
circuit switches off the power MOSFET. The controller
then waits until the UVLO level is reached on pin VCC.
When VCC drops to UVLO, capacitor CVCC will be
recharged to the Vstart level, however the IC will not start
switching again. Subsequently, VCC will drop again to the
UVLO level, etc.
2002 Aug 27
7
|
|
Share Link: 