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Preliminary data sheet

Rev. 01 — 28 May 2004

7 of 27

Philips Semiconductors

TEA1532

GreenChip

™II SMPS control IC

7.4 Oscillator

The fixed frequency of the oscillator is set by an internal current source and capacitor.

7.5 Cycle skipping

At very low power levels, a cycle skipping mode activates. An internal control voltage

this voltage increases to a higher value; see Figure 6.

7.6 Demagnetization (QR operation)

The system will be in Discontinuous Conduction Mode (DCM) (QR operation) when

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.

may be necessary in applications where the transformer has a large leakage inductance

and at low output voltages or start-up.

7.7 Continuous Conduction Mode (CCM)

It is also possible to operate the IC in the so-called Fixed Frequency Continuous

Conduction Mode (FF CCM). This mode is activated by connecting pin DEM to ground

7.8 Overcurrent Protection (OCP)

The current in the transformer primary is measured accurately by the internal

The accuracy of the current limit circuit allows the transformer core to have a minimum

specification for the output power required. The OCP circuit limits the ‘sense’ voltage to an

Leading Edge Blanking (LEB) circuit.

7.9 Control pin protection

If pin CTRL becomes open-circuit or is disconnected, a fault condition is assumed and the

converter will stop operating immediately. Operation recommences when the fault

condition is removed.

7.10 Adjustable slope compensation

A slope compensation function has been added at pin CTRL; see Figure 7. The slope

compensation function prevents sub-harmonic oscillation in CCM at duty cycles over

50 %. The CTRL voltage is modulated by sourcing a (non-constant) current out of

proportionally with the on-time, which therefore limits the OCP level. Thus, a longer

on-time results in a higher CTRL voltage, however, this increase in CTRL voltage will

actually decrease the on-time. Slope compensation can be adjusted by changing the