TEA1552 查看數據表（PDF） - Philips Electronics
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TEA1552 Datasheet PDF : 24 Pages
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Philips Semiconductors
GreenChip™II SMPS control IC
Product specification
TEA1552
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.
MGU236
handbook, halfpage
Vsense(max)
0.52 V
(typ)
In an optimum design, the reflected secondary voltage on
the primary side will force the drain voltage to zero. Thus,
0.3 V
zero voltage switching is very possible, preventing large
(typ)
capacitive switching losses P = 12-- × C × V2 × f , and
allowing high frequency operation, which results in small
and cost effective inductors.
−100 µA
(typ)
IDEM
−24 µA
(typ)
OverCurrent Protection (OCP)
The cycle-by-cycle peak drain current limit circuit uses the
external source resistor to measure the current accurately.
This allows optimum size determination of the transformer
core (cost issue). The circuit is activated after the leading
edge blanking time tleb. The OCP protection circuit limits
the ‘sense’ voltage to an internal level.
OverPower Protection (OPP)
During the primary stroke, the rectified mains input voltage
is measured by sensing the current drawn from pin DEM.
This current is dependent on the mains voltage, according
to the following formula: IDEM ≈ R--V---D--a--Eu---xM-- ≈ N------×-R----VD----Em---M-a---i-n--s-
where: N = -N--N--a---pu---x
The current information is used to adjust the peak drain
current, which is measured via pin Isense. The internal
compensation is such that an almost mains independent
maximum output power can be realized.
The OPP curve is given in Fig.9.
Fig.9 OPP correction curve.
Minimum and maximum ‘on-time’
The minimum ‘on-time’ of the SMPS is determined by the
Leading Edge Blanking (LEB) time. The IC limits the
‘on-time’ to 50 µs. When the system desires an ‘on-time’
longer than 50 µs, a fault condition is assumed, and the IC
will stop switching and enter the safe restart mode.
Short winding protection
After the leading edge blanking time, the short winding
protection circuit is also activated. If the ‘sense’ voltage
exceeds the short winding protection voltage Vswp, the
converter will stop switching. Once VCC drops below the
UVLO level, capacitor CVCC will be recharged and the
supply will restart again. This cycle will be repeated until
the short-circuit is removed (safe restart mode).
The short winding protection will also protect in case of a
secondary diode short-circuit.
2002 Aug 27
9
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