HA16116FP/FPJ, HA16121FP/FPJ
To Vref
C
T
V
DB
R
1
DB
E/O
5k
From UVL
0.8V
V
TH
V
E/O
V
DB
−
+
+
PWM
comparator
V
IN
V
TL
Booster
channel
1.6 V typ
1.0 V typ
On
t
ON
V
IN
Off
GND
V
IN
GND
t
OFF
C
ST
R
2
PWM
pulse
output
Step-down/
inverting
channel
Off
On
T
Figure 3.1 Dead Band Duty Setting
3.2 Soft Start (SST) Setting (each channel)
When the power is turned on, the soft start function gradually raises V
DB
(refer to section 3.1), and the
PWM output pulse width gradually widens. This function is realized by adding a capacitor C
ST
to the DB
pin. The function is realized as follows.
In the figure 3.2, the DB pin is clamped internally at approximately 0.8 V, which is 0.2 V lower than the
triangle wave V
TL
= 1.0 V typ.
t
A
: Standby time until PWM pulse starts widening.
t
B
: Time during which SST is in effect.
During soft start, the DB pin voltage in the figure below is as expressed in the following equation.
V
SST
= V
DB
⋅
1
−
e
Here,
t
0.8
=
−T
ln
1
−
0.8
V
DB
,
T = C
ST
⋅
(R
1
// R
2
)
−t −
t
0.8
T
,
t
SST
= t
A
+ t
B
How to select values: If the soft start time t
SST
is too short, the DC/DC converter output voltage will tend to
overshoot. To prevent this, set t
SST
to a few tens of ms or above.
Rev.2.0, Sep.18.2003, page 11 of 33
RENESAS [ RENESAS TECHNOLOGY CORP ]
