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參數(shù)資料
| 型號： | LT3641IUFD#TRPBF |
| 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： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件頁數(shù)： | 6/28頁 |
| 文件大?。?/td> | 416K |
| 代理商： | LT3641IUFD#TRPBF |
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LT3641
14
3641f
APPLICATIONS INFORMATION
where VOUT1 is high voltage channel output voltage, VD is
the forward voltage drop of the catch diode, and fS is the
switching frequency. For example, 3.3μH is a reasonable
inductance for a 3.3V output with 2MHz switching
frequency.
Once the inductance is selected, the inductor current ripple
and peak current can be calculated:
ΔIL1 =
(VOUT1 + VD)
L1 fS
1–
VOUT1 + VD
VIN
IL(PEAK) = IOUT(MAX) +
ΔIL
2
To guarantee sufcient output current, peak inductor
current 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:
L2
= 1.5
VOUT2
fS
For a selected inductance, the inductor current ripple can
be calculated:
ΔIL2 =
VOUT2
L2 fS
1–
VOUT2
VIN2
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 efciency 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 efciency converters generally
cannot afford the core loss found in low cost powdered
iron cores; instead use ferrite, molypermalloy or Kool Mμ
cores. Table 2 lists several vendors and suitable inductor
series.
Table 2. Inductor Vendors
VENDOR
WEBSITE
Murata
www.murata.com
TDK
www.tdk.com
TOKO
www.toko.com
Sumida
www.sumida.com
Cooper/Coiltronics
www.cooperindustries.com
Coilcraft
www.coilcraft.com
Vishay
www.vishay.com
NIC
www.niccomp.com
Würth Elektronik
www.we-online.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 efciency 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 nd optimum
inductors.
Low inductance may result in discontinuous mode oper-
ation, which is okay, but reduces maximum load current.
For details of maximum output current and discontinuous
mode operation, see the Linear Technology Application Note
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 LT3641 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 supply.
The input capacitor is required to reduce the resulting
voltage ripple. Use a ceramic capacitor with:
CIN ≥
10μF
fS
where fS in the switching frequency in MHz.
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