TEA1532 Philips Semiconductors, TEA1532 Datasheet - Page 7

• Manufacturer Part Number: TEA1532
• Description: GreenChip SMPS control IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 13113
Preliminary data sheet
7.10 Adjustable slope compensation
7.4 Oscillator
7.5 Cycle skipping
7.6 Demagnetization (QR operation)
7.7 Continuous Conduction Mode (CCM)
7.8 Overcurrent Protection (OCP)
7.9 Control pin protection
The fixed frequency of the oscillator is set by an internal current source and capacitor.
At very low power levels, a cycle skipping mode activates. An internal control voltage
(V
this voltage increases to a higher value; see
The system will be in Discontinuous Conduction Mode (DCM) (QR operation) when
resistor R
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 t
may be necessary in applications where the transformer has a large leakage inductance
and at low output voltages or start-up.
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
and connecting pin DRAIN to the rectified constant V
The current in the transformer primary is measured accurately by the internal
cycle-by-cycle source current limit circuit using the external sense resistor R
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
internal level, and is activated after the leading edge blanking period, t
Leading Edge Blanking (LEB) circuit.
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.
A slope compensation function has been added at pin CTRL; see
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
pin CTRL and adding a series resistor R
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
sense(max)
DEM
) lower than 25 mV will inhibit switch-on of the external power MOSFET until
is applied. The oscillator will not start a new primary stroke until the
Rev. 01 — 28 May 2004
slopecomp
Figure
. This increases the CTRL voltage
6.
i
voltage; see
GreenChip II SMPS control IC
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
supp
time. This suppression
Figure
Figure
leb
TEA1532
generated by the
7. The slope
13.
sense
.
7 of 27