MLP2012S datasheet(9/50 Pages) SII

9 / 50 page

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

Rev.2.0_01

S-8363 Series

2. Low voltage start-up

2. 1 Start-up circuit

The S-8363 Series can startup from 0.9 V. When the VOUT voltage at

OFF

= “H” does not reach the STU

release voltage, the start-up circuit starts the operation and outputs the fixed duty pulse to the CONT pin. By

this, the VOUT voltage starts step-up. After that, the VOUT voltage reaches the STU release voltage and the STU

mode circuit is set in STU release condition, therefore, the switching control circuit starts stable operation due

to the soft-start function. Simultaneously, the start-up circuit is set in disable condition, so that the S-8363

Series prevents excessive current consumption.

2. 2 Start-up mode (STU mode) circuit

The STU mode circuit monitors the VOUT voltage, and switches the operation modes between start-up period

and normal control period of the switching control circuit. The STU release voltage is internally fixed at 1.4 V

(typ.), and has hysteresis of approx. 0.15 V. When the VOUT voltage decreases to 1.25 V (typ.) from release

condition, the STU mode circuit is set in the STU detection condition, shifting to the start-up period. Several

μs

to several ten

μs is taken to shift from STU release to PWM release. During this the step-up operation is not

performed, therefore, the VOUT voltage may largely decrease depending on the size of load.

During applying

OFF

= “L”, the STU mode circuit is set in disable condition, so that the S-8363 Series

prevents excessive current consumption.

CONT

VOUT

MUX

Start-up

Circuit

VIN

VOUT

VIN

STU Mode Circuit

Load

L = 2.2

μH

COUT

μF

Switching

Control Circuit

VSS

Figure 8 Start-up Circuit

Time [s]

Switching delay

Output voltage

(VOUT)

Start-up period

CONT voltage

(VCONT)

PWM control period

STU detection

STU release

Figure 9 Start-up Sequence

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