PM6670AS datasheet(21/54 Pages) STMICROELECTRONICS

Teilenummer	PM6670AS

Bauteilbeschribung	Complete DDR2/3 memory power supplies controller

PDF	54 Pages

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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21 / 54 page

PM6670AS

Device description

21/54

The duty-cycle of the buck converter is, in steady-state conditions, given by

Equation 2

The switching frequency is thus calculated as

Equation 3

where

Equation 4a

Equation 4b

Referring to the typical application schematic (figures on cover page and Figure 27), the

final expression is then:

Equation 5

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's DCR) introduce voltage drops responsible for slight dependence on load current.

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

PM6670AS switching frequency can be set by an external divider connected to the VOSC

pin.

OUT

--------------

OSC

OUT

OSC

SNS

OSC

OUT

⋅

OSC

---------------

OUT

SNS

OUT

--------------

OSC

⋅

PM6670AS Datenblatt(PDF) 21 Page - STMicroelectronics