參數(shù)資料
型號: PM6675
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, QCC24
封裝: 4 X 4 MM, VFQFPN-24
文件頁數(shù): 29/47頁
文件大小: 650K
代理商: PM6675
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PM6675
Application information
35/47
The saturation current of the inductor should be greater than IL,PEAK as well as for case of
hard saturation core inductors. Using soft-ferrite cores is possible (but not advisable) to push
the inductor working near its saturation current.
In Table 9 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.
7.1.2
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 34
Neglecting the second term, the equation 10 is reduced to:
Equation 35
The losses due to the input capacitor are thus maximized when the duty-cycle is 0.5:
Equation 36
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 9. 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
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
+
=
)
D
1
(
D
I
LOAD
RMS
Cin
=
2
LOAD
Cin
2
CinRMS
Cin
loss
(max))
I
5
.
0
(
ESR
(max)
I
ESR
P
=
=
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