参数资料
型号: LTC3634EFE#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 5.5 A DUAL SWITCHING CONTROLLER, 4600 kHz SWITCHING FREQ-MAX, PDSO28
封装: 4.40 MM, LEAD FREE, PLASTIC, TSSOP-28
文件页数: 6/28页
文件大小: 359K
代理商: LTC3634EFE#PBF
LTC3634
14
3634f
applicaTions inForMaTion
core loss, greater ESR loss in the output capacitor, and
larger output voltage ripple. Generally, highest efficiency
operation is obtained at low operating frequency with
small ripple current.
A reasonable starting point is to choose a ripple current
somewhere between 600mA and 1.2A peak-to-peak. Note
that the largest ripple current occurs at the highest VIN.
Exceeding 1.8A is not recommended in order to minimize
outputvoltageripple.Toguaranteethatripplecurrentdoes
not exceed a specified maximum, the inductance should
be chosen according to:
L
=
VOUT
f
IL(MAX)
1
VOUT
VIN(MAX)
Once the value for L is known, the type of inductor must
be selected. Actual core loss is independent of core size
for a fixed inductor value, but is very dependent on the
inductance selected. As the inductance increases, core
losses decrease. Unfortunately, increased inductance
requires more turns of wire, leading to increased DCR
and copper loss.
Ferrite designs exhibit very low core loss and are pre-
ferred at high switching frequencies, so design goals
can concentrate on copper loss and preventing satura-
tion. Ferrite core material saturates “hard”, which means
that inductance collapses abruptly when the peak design
current is exceeded. This results in an abrupt increase in
inductor ripple current, so it is important to ensure that
the core will not saturate.
Differentcorematerialsandshapeswillchangethesize/cur-
rent and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and don’t radiate much energy, but generally cost
more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price versus size requirements
and any radiated field/EMI requirements. Table 1 gives a
sampling of available surface mount inductors.
Table 1. Inductor Selection Table
INDUCTANCE
(H)
DCR
(mΩ)
MAX
CURRENT (A)
DIMENSIONS
(mm)
HEIGHT
(mm)
Würth Electronik WE-HC 744310 Series
0.24
0.55
0.95
1.15
2.00
2.1
3.8
6.4
9.0
14.0
18.0
14.0
11.0
8.5
6.5
7
× 7
3.3
Vishay IHLP-2020BZ-01 Series
0.22
0.33
0.47
0.68
1
5.2
8.2
8.8
12.4
20
15
12
11.5
10
7
5.2
× 5.5
2
Toko FDV0620 Series
0.20
0.47
1.0
4.5
8.3
18.3
12.4
9.0
5.7
7
× 7.7
2.0
Coilcraft D01813H Series
0.33
0.56
1.2
4
10
17
10
7.7
5.3
6
× 8.9
5.0
TDK RLF7030 Series
1.0
1.5
8.8
9.6
6.4
6.1
6.9
× 7.3
3.2
CIN and COUT Selection
The input capacitance, CIN, is needed to filter the trapezoi-
dal wave current at the drain of the top power MOSFET.
To prevent large voltage transients from occurring, a low
ESR input capacitor sized for the maximum RMS current
is recommended. The maximum RMS current for a single
regulator is given by:
IRMS = IOUT(MAX)
VOUT VIN VOUT
(
)
VIN
When both regulators are active, the input current wave-
formissignificantlydifferent. Furthermore,theinputRMS
current varies depending on each output’s load current as
well as whether VTT is sinking or sourcing current.
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