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PM6670 データシート(PDF) 41 Page - STMicroelectronics

部品番号 PM6670
部品情報  Complete DDR2/3 memory power supply controller
PDF  53 Pages
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メーカー  STMICROELECTRONICS [STMicroelectronics]
ホームページ  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

PM6670 データシート(HTML) 41 Page - STMicroelectronics

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The saturation current of the inductor should be greater than IL,PEAK not only in case of hard
saturation core inductors. Using soft-ferrite cores it is possible (but not advisable) to push
the inductor working near its saturation current.
In Table 13 some inductors suitable for notebook applications are listed.
In Pulse-Skip Mode, low inductance values produce a better efficiency versus load curve,
while higher values result in higher full-load efficiency because of the smaller current ripple.
8.1.2
Input capacitor selection
In a buck topology converter the current that flows through the input capacitor is pulsed and
with zero average value. The RMS input current can be calculated as follows:
Equation 33
Neglecting the second term, the equation 10 is reduced to:
Equation 34
The losses due to the input capacitor are thus maximized when the duty-cycle is 0.5:
Equation 35
The input capacitor should be selected with a RMS rated current higher than ICINRMS(max).
Tantalum capacitors are good in terms of low ESR and small size, but they occasionally can
burn out if subjected to very high current during operation. Multi-Layers-Ceramic-Capacitors
(MLCC) have usually a higher RMS current rating with smaller size and they remain the best
choice. The drawback is their quite high cost.
Table 13. Evaluated inductors (@fsw = 400kHz)
Manufacturer
Series
Inductance (ìH)
+40°C rms
current (A)
-30% saturation
current (A)
COILCRAFT
MLC1538-102
1
13.4
21.0
COILCRAFT
MLC1240-901
0.9
12.4
24.5
COILCRAFT
MVR1261C-112
1.1
20
20
WURTH
7443552100
1
16
20
COILTRONICS
HC8-1R2
1.2
16.0
25.4
2
L
2
LOAD
RMS
Cin
)
I
(
D
12
1
)
D
1
(
D
I
I
∆
⋅
+
−
⋅
⋅
=
)
D
1
(
D
I
I
LOAD
RMS
Cin
−
⋅
=
2
LOAD
Cin
2
CinRMS
Cin
loss
(max))
I
5
.
0
(
ESR
(max)
I
ESR
P
⋅
⋅
=
⋅
=



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