HA16114P/PJ/FP/FPJ, HA16120FP/FPJ

Rev.2.0, Sep.18.2003, page 8 of 37

1.2 External Synchronization

These ICs have a sync input pin so that they can be synchronized to a primary-control AC/DC converter.

Pulses from the secondary winding of the switching transformer should be dropped through a resistor

voltage divider to the sync input pin. Synchronization takes place at the falling edge, which is optimal for

multiple-output power supplies that synchronize with a flyback AC/DC converter.

The sync input pin (

SYNC) is connected internally through a synchronizing circuit to the sawtooth

oscillator to synchronize the sawtooth waveform (see figure 1.2).

• Synchronization is with the falling edge of the external sync signal.

• The frequency of the external sync signal must be in the range f

• The duty cycle of the external sync signal must be in the range 5% < t

• With external synchronization, V

Note:

When not using external synchronization, connect the

SYNC pin to the Vref pin.

Sawtooth wave

SYNC pin

Synchronized

at falling edge

(1.0 V typ)

Vref

1 V

Figure 1.2 External Synchronization