HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
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.
t
soft
=
−C
1
×
R
×
ln (1
−
R=
R
1
×
R
2
R
1
+ R
2
R
2
R
1
+ R
2
V
X
)
V
DB
V
DB
= Vref
×
Note: V
X
is the voltage at the DB pin after time t (V
X
< V
DB
).
Undervoltage
lockout released
Sawtooth
To Vref wave
−
V
X
R
1
DB
+
C
1
R
2
from
UVL
UVL sink
transistor
t
Soft-start time
t
soft
E/O
+
PWM
COMP
V
TH
V
DB
V
TL
1.0 V
V
X
1.6 V
Sawtooth wave
Figure 3.2 Soft-Start Setting
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
1
in figure 3.2, which has a comparatively large
capacitance. In intermittent mode (explained on a separate page), this feature enables the IC to soft-start in
each on-off cycle.
Rev.2.0, Sep.18.2003, page 11 of 37
RENESAS [ RENESAS TECHNOLOGY CORP ]
