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参数资料
| 型号： | LT3663IMS8E-5#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V 1.2A 8MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 输入电压： | 7.5 V ~ 36 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1MHz |
| 电流 - 输出： | 1.2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 8-MSOP-EP |
| 产品目录页面： | 1332 (CN2011-ZH PDF) |
LT3663
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage of the LT3663 is programmed with a
resistor divider. Choose the 1% resistors according to:
R1 = R2 (V OUT /0.8 – 1)
Reference designators refer to the Block Diagram.
The resistor divider is internal on the fixed output voltage
versions, LT3663-X.
Minimum Duty Cycle
Figure 2. illustrates switching waveforms in pulse skip
mode a 3.3V output application with V IN = 30V.
V SW
20V/DIV
I L
1A/DIV
As the input voltage increases the duty cycle decreases. At
some point, the minimum duty cycle of the IC is reached
and pulse skipping begins. The output voltage continues to
regulate but the output voltage ripple increases. The input
voltage at which this occurs is calculated as follows:
V OUT
200mV/DIV
AC-COUPLED
2.5μs/DIV
Figure 2. Pulse-Skip Mode
3663 F02
V IN =
( V OUT + V F ) – V F + V SW
DC MIN
Inductor Selection
A good first choice for the inductor value is:
Where V F is the forward voltage drop of the catch diode,
D1, and V SW is the voltage drop on the internal switch,
Q1. LT3663 DC MIN is typically 0.12.
For V F = 0.4V, V SW = 0.3V, and V OUT = 3.3V pulse skipping
occurs at about 24.5V.
Figure 1 illustrates switching waveforms in normal mode
for a 3.3V output application with V IN = 20V.
V SW
20V/DIV
I L
1A/DIV
V OUT
200mV/DIV
AC-COUPLED
L = V OUT + V D (μH)
where V D is the voltage drop of the catch diode (~0.4V)
and L is in μH. With this value there is no sub-harmonic
oscillation for applications with 50% or greater duty
cycle. The inductor’s RMS current rating must be greater
than the maximum load current. Size the inductor so the
saturation current rating is about 30% higher than the
maximum load current. The output current limit circuit
tightly controls the maximum average inductor current,
therefore the inductor RMS current rating does not have
to be overrated to handle short circuit or overload condi-
tions. For high efficiency, keep the series resistance (DCR)
less than 0.1Ω. A higher value inductor is larger in size
and slows transient response but reduces output voltage
ripple. A lower value inductor has higher ripple currents
but is physically smaller or, for the same size, it has lower
DCR typically resulting in higher efficiency.
2.5μs/DIV
Figure 1. Normal Operation
3663 F01
8
For more information www.linear.com/LT3663
3663fc
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