PM6680 datasheet(22/49 Pages) STMICROELECTRONICS

부품명	PM6680

상세설명	No Rsense dual step-down controller with adjustable voltages for notebook system power

PDF	49 Pages

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제조업체	STMICROELECTRONICS [STMicroelectronics]

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Device description

PM6680

22/49

Figure 28.

Constant ON time PWM control

The duty cycle of the buck converter in steady state is:

Equation 2

The PWM control works at a nearly fixed frequency fSW:

Equation 3

As mentioned the steady state switching frequency is theoretically independent from battery

voltage and from output voltage.

Actually the frequency depends on parasitic voltage drops that are present during the

charging path(high side switch resistance, inductor resistance(DCR)) and discharging

path(low side switch resistance, DCR).

As a result the switching frequency increases as a function of the load current.

Standard switching frequency values can be selected for both sections by pin FSEL as

shown in the following table:

Table 6.

FSEL pin selection: typical switching frequency

Fsw@OUT1 = 1.5 V (kHz)

Fsw@OUT2 = 1.05 V (kHz)

FSEL = GND

200

325

FSEL = VREF

290

425

FSEL = LDO5

390

590

OUT

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OUT

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OUT

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⁄

PM6680 데이터시트(PDF) 22 Page - STMicroelectronics