L5988D datasheet(16/52 Pages) STMICROELECTRONICS

tên linh kiện	L5988D

Giải thích chi tiết về linh kiện	Pre-bias start up capability

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Functional description

L5988D

16/52

DocID15324 Rev 4

To improve the line transient performance, the voltage feed forward is implemented by

changing the slope of the sawtooth according to the input voltage change (see Figure 6 a).

Figure 6. Sawtooth: voltage feed forward

The slope of the sawtooth does not change if the oscillator frequency is increased by an

external signal or adjusted by the external resistor (see Figure 7). As a consequence the

gain of the PWM stage is a function of the switching frequency and its contribution must be

taken in account when performing the calculations of the compensation network (see

Section 6.4.1 on page 29 and Section 6.4.2 on page 33).

Figure 7. Sawtooth: synchronization and frequency adjust

Table 8. FSW resistor examples

R1 (k

)fSW (kHz)

R2 (k

)fSW (kHz)

198

360

450

215

180

499

245

120

548

261

594

295

711

110

322

801

150

343

915

220

361

1022

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