S-8337AAAA-P8T1G Datasheet, PDF (14/51 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8337/8338 Series
Rev.4.0_01
6. 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.
7. Operation
The following are basic equations [(1) through (7)] of the step-up switching regulator (refer to
Figure 10).
L
CONT
D
V_IN
V_OUT
M1
EXT
FB
C_L
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:
dlL
dt
=
VL
L
=
VIN − VS
L
…………………………………………………………………………………..…(2)
Integration of the above equation:
IL
=


VIN −
L
VS


•
t
…………………………………………………………………….…………….……(3)
IL flows while M1 is ON (ton). This time is determined by the oscillation frequency of OSC.
Peak current (IPK) after tON:
IPK
=


VIN −
L
VS


•
tON
……………………………………………………………………………………(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:
( ) VL = VOUT + VD^*2 − VIN _{……….………………………………………………………..………………(5)}
*2. VD: Diode forward voltage
The voltage on the CONT pin rises only by VOUT + VD.
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