FREQ datasheet(13/56 Pages) FUJITSU

13 / 56 page

MB39A214A

Limitation : development tool vendor use only

FUJITSU SEMICONDUCTOR CONFIDENTIAL

DS405-00007-1v0-E

FUNCTION

Bottom detection comparator system for low output voltage ripple

The bottom detection comparator system for low output voltage ripple determines the ON time (tON) using

the input voltage (VIN) and output voltage (VOUT) to hold the ON state to a specified period. During the OFF

period, the reference voltage (INTREF) is compared with the feedback voltage (FB) using the error

comparator (Error Comp.). When the feedback voltage (FB) is below the reference voltage (INTREF) ,

RS-FF is set and the ON period starts again. Switching is repeated as described above. Error Comp. is used

to compare the reference voltage (INTREF) with the feedback voltage (FB) to control the off-duty condition

in order to stabilize the output voltage.

This system adds the inductor current slope detected during the synchronous rectification period (tOFF) to

the reference voltage (INTREF) , and generates an output voltage slope during the OFF period, which is

essential for the bottom detection comparator system, in the IC. This enables the stable control operations

under the low output voltage ripple conditions.

Circuit diagram

Bias

tON

generator

Slope

Detector

Drive

Logic

INTREF

VREF

VIN

VOUT

Bias

Reg.

Lo-side

Drive

RS-FF

Hi-side

Drive

RS out

VIN

VOUT

tON

DRVH

DRVL

Waveforms

tON

tOFF

INTREF

DRVH

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