TEA1532 View Datasheet(PDF) - Philips Electronics

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TEA1532

GreenChip™II SMPS control IC

Philips Electronics 

Philips Semiconductors

TEA1532

GreenChip™II SMPS control IC

• When the voltage on pin CTRL is below 0.63 V, the IC is assumed to be out of

regulation (e.g. the control loop is open). In this case activating pin PROTECT

(VPROTECT > 2.5 V) will cause the converter to stop switching. Once VCC drops below

VUVLO, capacitor CVCC will be recharged and the supply will restart. This cycle will be

repeated until the fault condition is removed (safe restart mode)

• When the voltage on pin CTRL is above 0.63 V, the IC is assumed to be in regulation.

In this case activating pin PROTECT (VPROTECT > 2.5 V), by external means, will latch

the IC: The voltage on pin VCC will cycle between Vstart and VUVLO, but the IC will not

start switching again until the latch function is reset. The latch is reset as soon as VCC

drops below 4.5 V (typical value). The internal overtemperature protection will also

trigger this latch; see also Figure 1.

A voltage higher than 3 V on pin PROTECT will always latch the IC. This is independent of

the state of the IC.

7.13 Valley switching

Refer to Figure 8. 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 8 shows the drain voltage, valley signal, secondary stroke

signal 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 possible, preventing large capacitive

switching

losses

 P

=

12--

×

C

×

V2

×

f





,

and

allowing

high

frequency

operation,

which

results in small and cost effective magnetics.

9397 750 13113

Preliminary data sheet

Rev. 01 — 28 May 2004

© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

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