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V

+ V – V

OUT

F

IN

V

– V

OUT

IN

V

+ V – V

OUT

F

SAT

V

OUT

≈

I

LOAD

1 – D

V – V

IN

SAT

D

L

100,000

•

I

LOAD

∆I

IND

1 – D

2

+

I

LOAD

∆I

IND

1 – D

2

+

V

+ V

OUT

F

V

– V

OUT

SAT

I

LOAD

I

LOAD

∆I

IND

1 – D

2

+

I

LOAD

I

D

V

LOAD

IN

• •

1 – D

50 (1 – D)

+

0.25

Ω

(

(

2

D

1. Output Voltage Section

2. Inductor Selection (L)

TL3577

100-kHz CURRENT-MODE SIMPLE STEP-UP/FLYBACK SWITCHING REGULATOR

SLVS633 – OCTOBER 2006

Duty cycle

D

Average inductor current

Inductor current ripple

∆I

IND

Peak inductor current

Peak switch current

Switch voltage when off

Diode reverse voltage

Average diode current

Peak diode current

Power dissipation

(1)

These limits must be greater than or equal to the values specified in this application.

Resistors R1 and R2 are used to select the desired output voltage. These resistors form a voltage divider and

present a portion of the output voltage to the error amplifier, which compares it to an internal 1.23-V reference.

Select R1 and R2 such that:

A. Preliminary Calculations

To select the inductor, the calculation of the following three parameters is necessary:

E

• T, the product of volts • time that charges the inductor:

E

• T = D

µs)

13

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