S-8331 Seiko Instruments USA, S-8331 Datasheet - Page 14

• Manufacturer Part Number: S-8331
• Description: Step-Up Switching Regulator (DC/DC Converter ICs)
• Manufacturer: Seiko Instruments USA

14
STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL SWITCHING REGULATOR
S-8330/8331 Series
Operation
1. Step-Up DC-DC Converter
The S-8330/31 Series is a DC-DC converter using a pulse width modulation method (PWM) with low
current consumption. Conventional PFM DC/DC converters have a drawback. Namely, an increase in
the ripple voltage occurs because pulses are skipped when low output load current flows and the ripple
frequency of the output voltage varies. In the S-8330/31 Series, the pulse width varies in the range of 0
% to 72 % depending upon the load current, but the switching frequency does not vary. This allows the
ripple voltage due to switching to be reduced with a filter. Also, the internal soft start circuit controls the
rush current and the output voltage overshoot to be generated when the IC starts the step-up operation
by setting the power off pin to "H" level. At powering ON the IC, the rush current flows to charge up
capacitive components of output capacitor "C
The following are fundamental equations of step-up switching regulators [ (1) to (7) ] (see Figure 6).
The pin voltage at CONT immediatetly after M1 is turned ON (current I
Change in I
Integreation of the above equation (I
I
The peak current (I
The energy stored in L is represented by 1/2 L (I
When M1 is turned OFF (t
voltage (V
L
flows into L during t
V
(V
I
I
dI
L
PK
dt
A
S
L
=
= V
=
: Not saturated voltage of M1)
⎛
⎜
⎝
=
⎛
⎜
⎝
V
V
V
L
IN
S
L
L
IN
) generates.
L
−
L
=
L
−
V
with time:
V
V
S
S
IN
⎞
• ⎟
⎠
⎞
• ⎟
⎠
L
−
t
V
t
PK
V
ON
S
) after t
IN
ON
ON/OFF
. The time is determined depending upon the oscillating frequency of the OSC.
OFF
ON
:
), the energy stored in L is transmitted through a diode. Then reverse
OSC
L
Figure 6 Step-Up DC-DC Converter
L
Seiko Instruments Inc.
) is as follows:
CONT
M1
OUT
" and load via coils and diodes.
PK
)
Di
2
.
V
OUT
Electric
Volume
L
+
−
+
-
which flows into L is zero):
C
OUT
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(1)
(2)
(3)
(4)
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