S-8333CAAA-I8T1U Datasheet, PDF (13/44 Pages) Seiko Instruments Inc – PWM CONTROL SWITCHING REGULATOR CONTROLLER

STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
Rev.4.2_01
S-8333 Series
5. Error amplifier
The error amplifier outputs the PWM control signal so that the voltage of the FB pin is held at a specific value
(1 V). By connecting a resistor (RZ) and capacitor (CZ) to the output pin (CC pin) of the error amplifier in series,
an optional loop gain can be set, enabling stabilized phase compensation.
6. Operation
The following are basic equations [(1) through (7)] of the step-up switching regulator (refer to Figure 10).
L
CONT
D
VIN
VOUT
M1
EXT
FB
CL
VSS
Figure 10 Step-up Switching Regulator Circuit for Basic Equations
Voltage at the CONT pin at the moment M1 is turned ON (current IL flowing through L is zero), VA:
VA = VS^*1 ................................................................................................................................................. (1)
*1. VS: Non-saturated voltage of M1
Change in IL over time:
dl _L
dt
=
V_L
L
=
V_IN −
L
V_S
............................................................................................................................. (2)
Integration of the above equation:
I_L
=


V_IN
−
L
V_S


×
t
.................................................................................................................................. (3)
IL flows while M1 is ON (ton). This time is determined by the oscillation frequency of OSC.
Peak current (IPK) after tON:
I_PK
=


V_IN
−
L
V_S
 × t_ON

........................................................................................................................... (4)
The energy stored in L is represented by
1
2
×
L
(IPK)².
When M1 is turned OFF (tOFF), the energy stored in L is released via a diode, generating a reverse voltage (VL).
VL:
( ) V_L = V_OUT + V_D ^*2 − V_IN ......................................................................................................................... (5)
*2. VD: Diode forward voltage
The voltage on the CONT pin rises only by VOUT + VD.
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