HA16120FP HITACHI [Hitachi Semiconductor], HA16120FP Datasheet - Page 8

• Manufacturer Part Number: HA16120FP
• Description: Switching Regulator for Chopper Type DC/DC Converter
• Manufacturer: HITACHI [Hitachi Semiconductor]

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).
Note: When not using external synchronization, connect the SYNC pin to the Vref pin.
8
V
Sawtooth wave
(f
V
(1.0 V typ)
SYNC pin
(f
OSC
SYNC
TH
TL
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
(1.6 V typ)
)
)
V
TH
’ = (V
TH
Synchronized
at falling edge
V
TL
)
f
f
SYNC
Figure 1.2 External Synchronization
OSC
TH
' can be calculated as follows.
+ V
TL
t
OSC
2
t
1
< f
1
SYNC
/t
2
< 50% (t
< f
OSC
1
2.
= 300 ns Min).
1 V
V
Vref
TH