參數(shù)資料
型號(hào)： LT3640IUFD#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： 3.4 A DUAL SWITCHING CONTROLLER, 2350 kHz SWITCHING FREQ-MAX, PQCC28
封裝： 5 X 4 MM, LEAD FREE, PLASTIC, MO-220, QFN-28
文件頁(yè)數(shù)： 6/24頁(yè)
文件大小： 506K
代理商： LT3640IUFD#PBF
LT3640
3640f
applicaTions inForMaTion
To guarantee sufficient output current, peak inductor cur-
rent must be lower than the switch current limit (ILIM).
The largest inductor current ripple occurs at the highest
VIN. To guarantee current capacity, use VIN(MAX) in the
above formula.
The inductance for the low voltage channel is:
L
V
f
OUT
S
2 1 5
2
= .
For a selected inductance, the inductor current ripple can
be calculated:
I
V
L f
V
L
OUT
S
OUT
IN
2
1
=
–
For robust operation in fault conditions, the inductor
saturation current should be higher than the upper limit
of the corresponding top switch current limit.
To keep the efficiency high, the inductor series resistance
(DCR) should be as small as possible (must be < 0.1Ω),
and the core material should be intended for the chosen
operation frequency. High efficiency converters generally
cannot afford the core loss found in low cost powdered
iron cores; instead use ferrite, molypermalloy or Kool M
cores. Table 2 lists several vendors and suitable inductor
series.
Table 2. Inductor Vendors
PART SERIES
VENDOR
LQH55D
Murata
www.murata.com
SLF7045
SLF10145
TDK
www.componenttdk.com
D62CB, D63CB
D75C, D75F
TOKO
www.toko.com
CR54, CDRH74
CDRH6D38, CR75
Sumida
www.sumida.com
Of course, such a simple design guide will not always
result in the optimum inductors for the applications. A
larger value inductor provides a slightly higher maximum
load current and will reduce the output voltage ripple. A
larger value inductor also results in higher efficiency in the
condition of same DCR and same magnetic loss. However,
for a same series of inductors, a larger value inductor has
higher DCR. The trade-off between inductance and DCR
is not always obvious. Use experiments to find optimum
inductors.
Low inductance may result in discontinuous mode opera-
tion, which is okay, but reduces maximum load current.
For details of maximum output current and discontinuous
modeoperation,seetheLinearTechnologyApplicationNote
44. For duty cycles greater than 50%, there is a minimum
inductance required to avoid subharmonic oscillations.
See the Linear Technology Application Note 19.
Input Capacitor
Bypass the VIN pin of the LT3640 with a ceramic capacitor
of X7R (–55°C to 125°C) or X5R (–55°C to 85°C) type.
Buck converters draw pulse current from the input sup-
ply. The input capacitor is required to reduce the resulting
voltage ripple. Use a ceramic capacitor with:
C
F
f
IN
S
≥
10
where fS in the switching frequency in MHz.
Asecondprecautionregardingtheceramicinputcapacitor
concerns the maximum input voltage rating of the LT3640.
A ceramic input capacitor combined with trace or cable
inductanceformsaunderdampedtankcircuit.IftheLT3640
circuit is plugged into a live supply, the input voltage can
ring to twice its nominal value, possibly exceeding the
LT3640’svoltagerating.Thissituationcanbeeasilyavoided
(see the Linear Technology Application Note 80).
相關(guān)PDF資料
PDF描述
LT3640EUFD#TRPBF 3.4 A DUAL SWITCHING CONTROLLER, 2350 kHz SWITCHING FREQ-MAX, PQCC28
LT3640IUFD#TRPBF 3.4 A DUAL SWITCHING CONTROLLER, 2350 kHz SWITCHING FREQ-MAX, PQCC28
LT3645IUD#TRPBF 1.25 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PQCC16
LT3645IUD#PBF 1.25 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PQCC16
LT3645EUD#TRPBF 1.25 A SWITCHING REGULATOR, 825 kHz SWITCHING FREQ-MAX, PQCC16
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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