s-8333aaca-t8t1g Seiko Instruments Inc., s-8333aaca-t8t1g Datasheet - Page 9

• Manufacturer Part Number: s-8333aaca-t8t1g
• Description: Step-up, For Lcd Bias Supply, 1-channel, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

Rev.2.3
STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
Operation
1. Switching control method
2. Soft-start function
1. 1 PWM control
The pulse width of the S-8333 Series varies from 0% to the maximum duty set by RDuty depending on the load
current, but its switching frequency does not change. Consequently, the ripple voltage generated from switching
can be removed easily via a filter.
For this IC, the built-in soft-start circuit controls the rush current and overshoot of the output voltage when
powering on. Reference voltage adjustment and maximum duty control methods are adopted as the soft-start
methods. The following describes the soft-start function at power application.
In the circuit where the input voltage is not directly output at shutdown by inserting a switch (SW) between the
diode (SD) and V
Therefore, the voltage of the FB pin stays 0 V and the EXT output is in the step up status between the “H” and “L”
levels due to the maximum duty. The maximum duty at this time is approximately 7% and the rush current at
power application is controlled. The maximum duty soft start is accomplished by gradually increasing the duty
width up to the maximum duty set by the external resistor RDuty (refer to Figure 8).
The reference voltage of the error amplifier input also gradually increases from 0 V at the same time as the
maximum duty soft start. The increasing of the output voltage is controlled by turning the SW ON. The soft-start
function is realized by controlling the voltage of the FB pin so that it is the same potential as the reference voltage
that is slowly raised. A Rail-to-Rail amplifier is adopted as the error amplifier, which means that the voltage is
loop controlled so that it can be the same as the reference voltage.
Once the reference voltage rises, the voltage cannot be reset (the reference voltage is 0 V) unless making the
power supply voltage lower than the UVLO detection voltage. Conversely, when the power supply voltage rises
up to the reset voltage after it is lowered to the UVLO detection voltage or lower, the output voltage is stepped up
by the soft-start function.
The S-8333 Series is a DC-DC converter using a pulse width modulation method (PWM).
_00
V
IN
OUT
L
output, the V
M1
EXT
OUT
PWM
Comparator
Seiko Instruments Inc.
CZ
CC
RZ
voltage when the V
+
−
Figure 7
Error amplifier
SD
+
−
Error amplifier
reference voltage
IN
0.5 V
0 V
voltage is applied with the SW OFF stays 0 V.
SW
V
FB
ref
RFB1
RFB2
C
V
L
OUT
S-8333 Series
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