Ricoh RV5VH User Manual

Page 43

RV5VH3

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• DC/DC Converter 2

The DC/DC2 can operate by an input voltage to the V

pin. A change in the V

OUT2

will feed back to the internal error

amplifier through external voltage setting resistors. The V

REF

voltage should be provided from externally fixed power sup-

ply such as V

OUT1

When the feed back voltage to the Error Amp.2 is higher than the ground voltage the error amplifier enables oscillation or

otherwise will stop oscillation.

Pulses from the “OSC” circuit have a duty cycle of 50% and it makes VFM operation allowable.

There might be certain cases that the duty cycles becomes smaller temporally at light load current. The output of “EXT2”

is driven by CMOS buffer operated V

and GND.

A PMOS driver will be connected to the “EXT2” pin and its switching operation generates negative output voltage through

energy accumulated in an inductor.

The DC/DC1 can be shut down by CSW pin. When the CSW pin is High, V

level, the DC/DC1 is enabled and when the

CSW pin is Low, GND level, the DC/DC1 is disabled. The EXT2 pin outputs High while the DC/DC2 is disabled.

• Set Output Voltage DC/DC 2

OUT2

is described as follows:

REF

: R1=|–V

OUT2

| : R2

The FB2 voltage is controlled to 0V and V

REF

is provided externally

|–V

OUT2

|=V

REF

R2/R1

so any output voltage of DC/DC2 can be set by changing R1 or/and R2.

Certain temperature coefficient of V

OUT2

can be set by using R1, R2 having such temperature characteristics.

FB2

OUT2

EXT2

–

RV5VH3

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Error Amp.2

VFM2

CSW

SBD

PMOS

OSC

REF