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PM6670 Fiches technique(PDF) 39 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) 39 Page - STMicroelectronics

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PM6670
Application information
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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's 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
11
250
330
13
300
330
15
350
330
18
400
330
20
450
330
22
500
IN
OSC
OSC
V
V
=
α
OUT
SNS
OUT
V
V
=
α
OSC
2
1
2
OSC
OSC
SW
K
1
R
R
R
K
f
⋅
+
=
α
=



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