2003 May 12

7

Philips Semiconductors

Product specification

GreenChip

™II SMPS control IC

TEA1654

handbook, full pagewidth

MDB219

1.5 V

− VCTRL

fosc

fmax

fmin

Vx (mV)

CTRL

VCC(5V)

current

comparator

cycle

skipping

X2

V

I

1

0

Vx

OSCILLATOR

DRIVER

DRIVER

5 V

Vx (mV)

Vx (mV)

dV4

dV2

dV1

dV3

VSTDBY

(V)

5

0

VCOadj

VCOadj

Isense

Fig.7 A functional implementation of the standby and cycle skipping circuitry.

The level at which VCO mode of operation starts or ends can be controlled externally with the VCOadj pin.

Standby output

an external NPN transistor or FET in order to e.g.

switch-off a PFC circuit. The STDBY output is activated by

the internal VCO: as soon as the VCO has reduced the

switching frequency to (almost) the minimum frequency of

24 kHz, the STDBY output will be activated (see Fig.7).

The STDBY output will go low again as soon as the VCO

allows a switching frequency close to the maximum

frequency of 65 kHz.

Demagnetization

The system will be in discontinuous conduction mode all

the time. The oscillator will not start a new primary stroke

until the secondary stroke has ended.

Demagnetization features a cycle-by-cycle output

short-circuit protection by immediately lowering the

frequency (longer off-time), thereby reducing the power

level.

Demagnetization recognition is suppressed during the first

applications where the transformer has a large leakage

inductance and at low output voltages/start-up.

OverVoltage Protection (OVP)

An OVP mode is implemented in the GreenChip series.

For the TEA1654, this works by sensing the auxiliary

voltage via the current flowing into pin DEM during the

secondary stroke. The auxiliary winding voltage is a

well-defined replica of the output voltage. Any voltage

spikes are averaged by an internal filter.

If the output voltage exceeds the OVP trip level, the OVP

circuit switches off the power MOSFET. The controller

UVLO level, etc.