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Step-Up (Boost) Regulator

Step-Up Regulator Design Procedure

V

SW(OFF)

V

SAT

0 V

0 V

0

0

0

V

F

V

R

I

IND(AVG)

I

SW(PK)

I

D(PK)

I

D(AVG)

∆I

IND

Switch

Voltage

Diode

Voltage

Inductor

Current

Switch

Current

Diode

Current

TL3577

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

SLVS633 – OCTOBER 2006

APPLICATION INFORMATION (continued)

Figure 2 shows a step-up switching regulator utilizing the TL3577. The regulator produces an output voltage

higher than the input voltage. The TL3577 turns its switch on and off at a fixed frequency of 100 kHz, thus

energy stored in the inductor is thus transferred to the output. The output voltage is controlled by the amount of

energy transferred, which is controlled by modulating the peak inductor current. This modulation is accomplished

by feeding a portion of the output voltage to an error amplifier that amplifies the difference between the feedback

voltage and an internal 1.23-V precision reference voltage. The output of the error amplifier is compared to a

voltage that is proportional to the switch current or the inductor current during the switch-on time. A comparator

terminates the switch-on time when the two voltages are equal and, thus, controls the peak switch current to

maintain a constant output voltage. Figure 5 shows voltage and current waveforms for the circuit. Formulas for

calculation are shown in Table 1.

Given:

Figure 5. Step-Up Regulator Waveforms

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