PM6670S datasheet(39/53 Pages) STMICROELECTRONICS

tên linh kiện	PM6670S

Giải thích chi tiết về linh kiện	Complete DDR2/3 memory power supply controller

PDF	53 Pages

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39 / 53 page

PM6670S

Application information

39/53

where

Equation 27a

Equation 27b

Referring to the typical application schematic (figure in cover page and Figure 29), the final

expression is then:

Equation 28

The switching frequency directly affects two parameters:

●

Inductor size: greater frequencies mean smaller inductances. In notebook applications,

real estate solutions (i.e. low-profile power inductors) are mandatory also with high

saturation and r.m.s. currents.

●

Efficiency: switching losses are proportional to the frequency. Generally, higher

frequencies imply lower efficiency.

Even if the switching frequency is theoretically independent from battery and output

voltages, parasitic parameters involved in power path (like MOSFETs on-resistance and

inductor DCR) introduce voltage drops responsible for a slight dependence on load current.

In addition, the internal delay is due to a light dependence on input voltage.

Table 12.

Typical values for switching frequency selection

R1 (k

Ω)R2 (kΩ)

Approx switching frequency (kHz)

330

250

330

300

330

350

330

400

330

450

330

500

OSC

OUT

SNS

OUT

OSC

⋅

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