PM6670AS View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'PM6670AS' PDF : 54 Pages View PDF
PM6670AS
Device description
The duty-cycle of the buck converter is, in steady-state conditions, given by
Equation 2
D = -V----O----U---T--
VIN
The switching frequency is thus calculated as
Equation 3
where
VOUT
fSW
=
D
TON
=
VIN
K OSC
VSNS
VOSC
= αOSC ⋅ 1
αOUT KOSC
Equation 4a
αOSC
=
V-----O----S---C--
VIN
Equation 4b
αOUT
=
-V----S---N----S--
VOUT
Referring to the typical application schematic (figures on cover page and Figure 27), the
final expression is then:
Equation 5
fSW
= αOSC
K OSC
= R2
R1 + R2
⋅1
K OSC
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.
Doc ID 14436 Rev 2
21/53
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