AN3392 datasheet(9/57 Pages) STMICROELECTRONICS

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AN3392

Application information

Doc ID 018749 Rev 1

9/57

Application information

A step-up (or boost) converter is a switching DC-DC converter able to generate an output

voltage higher than the input voltage.

Figure 5.

Step-up converter single-ended architecture

The switching element (Sw) is typically driven by a fixed-frequency rectangular waveform

generated by a PWM controller.

When Sw is closed (Ton), the inductor stores energy and its current increases with a slope

depending on the voltage across the inductor and its inductance value. During this time the

output voltage is sustained by Cout and the diode doesn’t allow any charge transfer from

output to input stages.

When Sw is open (Toff) the current in the inductor flows toward the output until the voltage

on node “A” is higher than the output voltage. During this phase the current in the inductor

decreases while the output voltage increases.

Figure 6 shows the behavior of the current on the inductor.

Figure 6.

Step-up converter in continuous mode

Comparing the energy stored in the inductor during Ton and the energy released during Toff,

the relation between VOUT and Vin is:

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