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PM6670 Fiches technique(PDF) 21 Page - STMicroelectronics

No de pièce PM6670
Description  Complete DDR2/3 memory power supply controller
PDF  53 Pages
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Fabricant  STMICROELECTRONICS [STMicroelectronics]
Site Internet  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

PM6670 Fiches technique(HTML) 21 Page - STMicroelectronics

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PM6670
Device description
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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 29), 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 PM6670
switching frequency can be set by an external divider connected to the VOSC pin.
Figure 29. Switching frequency selection and VOSC pin
The voltage seen at this pin must be greater than 0.8V and lower than 2V in order to ensure
the system's linearity.
D
V
OUT
V
IN
--------------
=
OSC
OUT
OSC
OSC
SNS
OSC
IN
OUT
ON
SW
K
1
V
V
K
V
V
T
D
f
⋅
α
α
=
=
=
α
OSC
V
OSC
V
IN
---------------
=
α
OUT
V
SNS
V
OUT
--------------
=
OSC
2
1
2
OSC
OSC
SW
K
1
R
R
R
K
f
⋅
+
=
α
=
PM6670
VOSC
R1
R2
VIN



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