S-8363 Просмотр технического описания (PDF) - Seiko Instruments Inc

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S-8363

STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM / PFM SWITCHABLE SWITCHING REGULATOR

Seiko Instruments Inc 

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

VIN

I1

Nch power

MOS FET

SD

I2

VOUT

IOUT

CONT

FB

VSS

COUT

RL

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

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