HA16114P Datasheet, PDF (8/38 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
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_OSC < f_SYNC < f_OSC × 2.
• The duty cycle of the external sync signal must be in the range 5% < t₁/t₂ < 50% (t₁ = 300 ns Min).
• With external synchronization, V_TH' can be calculated as follows.
V_TH’ = (V_TH − V_TL) ×
f_OSC
f_SYNC
+ V_TL
Note: When not using external synchronization, connect the SYNC pin to the Vref pin.
V_TH (1.6 V typ)
Sawtooth wave
(f_OSC)
V_TL
(1.0 V typ)
SYNC pin
(f _SYNC )
Synchronized
t₁
at falling edge
t₂
Figure 1.2 External Synchronization
V_TH
Vref
1V
8