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TEA1532CT View Datasheet(PDF) - NXP Semiconductors.

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TEA1532CT
NXP
NXP Semiconductors. NXP
TEA1532CT Datasheet PDF : 23 Pages
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NXP Semiconductors
TEA1532BT; TEA1532CT
GreenChip II SMPS control IC
Vsense(max) (V)
coa016
0.52 V
cycle
skip
active
25 mV
1V
(typ)
1.5 V
(typ) VCTRL (V)
Fig 5. The Vsense(max) voltage as a function of VCTRL
7.6 OverCurrent Protection (OCP)
The primary peak current in the transformer is measured accurately cycle-by-cycle using
the external sense resistor Rsense. The OCP circuit limits the voltage on pin SENSE to an
internal level equal to 1.5 V VCTRL (see also Section 7.5). The OCP detection is
suppressed during the leading edge blanking period, tleb, to prevent false triggering
caused by the switch-on spikes.
7.7 Demagnetization (QR operation)
The system will be in Discontinuous Conduction Mode (DCM) (QR operation) when
resistor RDEM is applied. The oscillator will not start a new primary stroke until the previous
secondary stroke has ended.
Demagnetization features a cycle-by-cycle output short-circuit protection, which
immediately reduces the frequency (longer off-time), thereby reducing the power level.
Demagnetization recognition is suppressed during the first tsup(xfmr_ring) time (typical
1.5 µs). This suppression may be necessary in applications where the transformer has a
large leakage inductance and at low output voltages or start-up.
7.8 Valley switching
Refer to Figure 6. A new cycle starts when the power switch is activated. After the on-time
(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 --------------------1----------------------
2 × π × Lp × Cd
where Lp is the primary self inductance of the transformer and Cd is the capacitance on
the drain node.
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 6 shows the drain voltage, valley signal, secondary stroke
signal and the oscillator signal.
TEA1532BT_TEA1532CT_1
Product data sheet
Rev. 01 — 18 January 2007
© NXP B.V. 2007. All rights reserved.
7 of 23
 

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