FSP3601 datasheet(7/14 Pages) FOSLINK

7 / 14 page

STEP-UP DC/DC CONTROLLER

2007-6-6

7/14

FSP3601

TIMING WAVEFORM

DETAILED DESCRIPTION

Voltage reference

A 1.25V regulator operating from VCC is used to power the internal circuitry of the FSP3601. An internal resister

divider provides 0.5V reference for the error amplifier, Soft-start (typ. 0.9V) and SCP (typ.0.8V).

Error amplifier

The error amplifier compares a sample of the dc-dc converter output voltage to the 0.5V reference and generates an

error signal for the PWM comparator. Output voltage of the dc-dc converter is setting with the resistor divider using

the following expression (see fig12):

VOUT = (1+R1/ R2)*0.5

Figure 12. Error Amplifier with Feedback resistance divider

OFF

Power supply control

Soft start

Output

short

circuit

Output short circuit

tpe

Short circuit

detection

SCP pin waveforms

OUT pin waveforms

Soft start setting voltage

Idle period setting voltage

Reference input for short circuit

detection comparator

COMP pin voltage

500

Vout

FSP3601

Error Amplifier

36K

0.5V

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