S-8363B-I6T1U2 Datasheet, PDF (15/50 Pages) Seiko Instruments Inc – PWM/PFM SWITCHABLE SWITCHING REGULATOR

STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM/PFM SWITCHABLE SWITCHING REGULATOR
Rev.2.0_01
S-8363 Series
 Operation Principles
The S-8363 Series is a step-up switching regulator. Figure 14 shows the basic circuit diagram.
Step-up switching regulators start current supply by the input voltage (VIN) when the Nch power MOS FET is turned
on and holds energy in the inductor at the same time. When the Nch power MOS FET is turned off, the CONT pin
voltage is stepped up to discharge the energy held in the inductor and the current is discharged to VOUT through the
diode. When the discharged current is stored in COUT, a voltage is generated, and the potential of VOUT increases
until the voltage of the FB pin reaches the same potential as the internal reference voltage.
For the PWM control method, the switching frequency (fOSC) is fixed and the VOUT voltage is held constant
according to the ratio of the ON time and OFF time (ON duty) of the Nch power MOS FET in each period.
In the PWM control method, the VOUT voltage is held constant by controlling the ON time.
In the PFM control method, the Nch power MOS FET is turned on by fixed duty. When energy is discharged to VOUT
once and the VOUT potential exceeds the set value, the Nch power MOS FET stays in the off status until VOUT
decreases to the set value or less due to the load discharge. Time VOUT decreases to the set value or less depends
on the amount of load current, so, the switching frequency varies depending on this current.
L
V_IN
I₁
Nch power
MOS FET
SD
I₂
V_OUT
I_OUT
CONT
FB
VSS
C_OUT
R_L
Figure 14 Basic Circuit of Step-up Switching Regulator
The ON duty in the current continuous mode can be calculated by using the equation below. Use the S-8363 Series
in the range where the ON duty is less than the maximum duty.
The maximum duty is 88% (typ.).
( ) ^{ON duty =}
1−
VIN
VOUT + VD^*1
× 100 [%]
*1. VD : Forward voltage of diode
15