参数资料
| 型号： | LTC3411IMS#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 10MSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.8 V ~ 5 V |
| 输入电压： | 2.63 V ~ 5.5 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 1MHz |
| 电流 - 输出： | 1.25A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-MSOP |
LTC3411
APPLICATIONS INFORMATION
? ? 1 ? OUT ?
V OUT ? V ?
R T = 9 . 78 ? 10 11 ( f O )
( Ω )
AgeneralLTC3411applicationcircuitisshowninFigure 5.
External component selection is driven by the load require-
ment, and begins with the selection of the inductor L1.
Once L1 is chosen, C IN and C OUT can be selected.
Operating Frequency
Selection of the operating frequency is a tradeoff between
ef?ciency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves ef?ciency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency, f O , of the LTC3411 is determined
by an external resistor that is connected between the R T
pin and ground. The value of the resistor sets the ramp
current that is used to charge and discharge an internal
timing capacitor within the oscillator and can be calculated
by using the following equation:
? 1 . 08
The minimum frequency is limited by leakage and noise
coupling due to the large resistance of R T .
Inductor Selection
Although the inductor does not in?uence the operat-
ing frequency, the inductor value has a direct effect on
ripple current. The inductor ripple current Δ I L decreases
with higher inductance and increases with higher V IN or
V OUT :
Δ I L =
f O ? L ? V IN ?
Accepting larger values of Δ I L allows the use of low induc-
tances, but results in higher output voltage ripple, greater
core losses, and lower output current capability.
A reasonable starting point for setting ripple current is 40%
of maximum output current, or Δ I L = 0.4 ? 1.25A = 500mA.
The largest ripple current Δ I L occurs at the maximum input
voltage. To guarantee that the ripple current stays below a
speci?ed maximum, the inductor value should be chosen
according to the following equation:
? ? 1 ?
or can be selected using Figure 2.
The maximum usable operating frequency is limited by
the minimum on-time and the duty cycle. This can be
L =
V OUT
f O ? Δ I L
?
?
V OUT ?
V IN ( MAX ) ? ?
calculated as:
f O(MAX) ≈ 6.67 ? (V OUT / V IN(MAX) ) (MHz)
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
T A = 25°C
The inductor value will also have an effect on Burst Mode
operation. The transition from low current operation
begins when the peak inductor current falls below a level
set by the burst clamp. Lower inductor values result in
0
500
1000
1500
R T (kΩ)
3411 F02
Figure 2. Frequency vs R T
3411fb
9
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