HA16120FP HITACHI [Hitachi Semiconductor], HA16120FP Datasheet - Page 11

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

3.2 Soft-Start Setting
Soft-start avoids overshoot at power-up by widening the PWM output pulses gradually, so that the
converted DC output rises slowly. Soft-start is programmed by connecting a capacitor between the DB pin
and ground. The soft-start time is determined by the time constant of this capacitor and the resistors that
set the voltage at the DB pin.
Note: V
3.3 Quick Shutdown
The quick shutdown function resets the voltages at all pins when the IC is turned off, to assure that PWM
pulse output stops quickly. Since the UVL pull-down resistor in the IC remains on even when the IC is
turned off, the sawtooth wave output, error amplifier output, and DB pin are all reset to low voltage.
This feature helps in particular to discharge capacitor C
capacitance. In intermittent mode (explained on a separate page), this feature enables the IC to soft-start in
each on-off cycle.
V
C
X
1
X
R
R
To Vref
t
R =
V
is the voltage at the DB pin after time t (V
soft
1
2
DB
= C
= Vref
R
R
DB
1
1
+ R
Sawtooth
wave
1
R
E/O
2
2
R
R
UVL sink
transistor
1
R
ln (1
+ R
2
+
+
2
from
UVL
V
V
PWM
COMP
DB
X
Figure 3.2 Soft-Start Setting
)
V
V
V
HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
TH
DB
TL
X
1.6 V
1.0 V
< V
Undervoltage
lockout released
1
DB
in figure 3.2, which has a comparatively large
).
Soft-start time
t
soft
Sawtooth wave
V
X
t
11