参数资料
| 型号： | LT1938IDD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2.2A 10DFN |
| 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： | 1.27 V ~ 20 V |
| 输入电压： | 3.6 V ~ 25 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 300kHz ~ 2.8MHz |
| 电流 - 输出： | 2.2A |
| 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： | 10-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-DFN（3x3） |
LT1938
APPLICATIONS INFORMATION
R1 = R2 ? OUT – 1 ?
f SW ( MAX ) =
t ON ( MIN ) ( V D IN – V SW )
V IN ( MAX ) =
V OUT + V D
f SW t ON ( MIN )
FBResistorNetwork
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
? V ?
? 1.265 ?
Reference designators refer to the Block Diagram.
Setting the Switching Frequency
The LT1938 uses a constant frequency PWM architecture
that can be programmed to switch from 300kHz to 2.8MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary R T value for a desired switching
frequency is in Figure 1.
SWITCHING FREQUENCY (MHz) R T VALUE (k ? )
0.2 267
0.3 187
0.4 133
0.6 84.5
0.8 60.4
1.0 45.3
1.2 36.5
1.4 29.4
1.6 23.7
1.8 20.5
2.0 16.9
2.2 14.3
2.4 12.1
2.6 10.2
2.8 8.66
Figure 1. Switching Frequency vs R T Value
Operating Frequency Tradeoffs
Selection of the operating frequency is a tradeoff between
efficiency, component size, minimum dropout voltage, and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (f SW(MAX) ) for a
given application can be calculated as follows:
V D + V OUT
+ V
where V IN is the typical input voltage, V OUT is the output
voltage, is the catch diode drop (~0.5V), V SW is the internal
switch drop (~0.5V at max load). This equation shows
that slower switching frequency is necessary to safely
accommodate high V IN /V OUT ratio. Also, as shown in
the next section, lower frequency allows a lower dropout
voltage. The reason input voltage range depends on the
switching frequency is because the LT1938 switch has
finite minimum on and off times. The switch can turn on
for a minimum of ~150ns and turn off for a minimum of
~150ns. This means that the minimum and maximum
duty cycles are:
DC MIN = f SW t ON ( MIN )
DC MAX = 1– f SW t OFF ( MIN )
where f SW is the switching frequency, the t ON(MIN) is the
minimum switch on time (~150ns), and the t OFF(MIN) is
the minimum switch off time (~150ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
A good choice of switching frequency should allow ad-
equate input voltage range (see next section) and keep
the inductor and capacitor values small.
Input Voltage Range
The maximum input voltage for LT1938 applications de-
pends on switching frequency, the Absolute Maximum Rat-
ings on V IN and BOOST pins, and on operating mode.
If the output is in start-up or short-circuit operating modes,
then V IN must be below 25V and below the result of the
following equation:
– V D + V SW
where V IN(MAX) is the maximum operating input voltage,
V OUT is the output voltage, V D is the catch diode drop
(~0.5V), V SW is the internal switch drop (~0.5V at max
load), f SW is the switching frequency (set by R T ), and
t ON(MIN) is the minimum switch on time (~150ns). Note that
a higher switching frequency will depress the maximum
operating input voltage. Conversely, a lower switching
1938fa
10
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| LT1939 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
| LT1939EDD#PBF | 功能描述:IC REG DL BUCK/LINEAR 12DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT1939EDD#TRPBF | 功能描述:IC REG DL BUCK/LINEAR 12DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT1939EDD-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
| LT1939EDD-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
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