参数资料
| 型号： | LT3682IDD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1A 12DFN |
| 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 ~ 20 V |
| 输入电压： | 3.6 V ~ 36 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 250kHz ~ 2.2MHz |
| 电流 - 输出： | 1A |
| 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： | 12-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 12-DFN |
LT3682
APPLICATIONS INFORMATION
R 1 = R 2 ? OUT ? 1 ?
f SW ( MAX ) =
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to:
? V ?
? 0 . 8 V ?
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.
Setting the Switching Frequency
The LT3682 uses a constant frequency PWM architecture
that can be programmed to switch from 250kHz to 2.2MHz
by using a resistor tied from the R T pin to ground. A table
showing the necessary R T value for a desired switching
frequency is in Figure 1.
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower ef?ciency, 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 OUT + V D
t ON ( MIN ) ( V IN ? V SW + V D )
where V IN is the typical input voltage, V OUT is the output
voltage, V D is the catch diode drop (~0.5V) and 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 Input Voltage Range section, lower frequency allows
a lower dropout voltage. Input voltage range depends on
the switching frequency because the LT3682 switch has
?nite minimum on and off times. An internal timer forces
the switch to be off for at least t OFF(MIN) per cycle; This
SWITCHING FREQUENCY (MHz)
0.25
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.4
1.6
1.8
2.0
R T VALUE (kΩ)
158
127
90.9
71.5
57.6
47.5
40.2
34
29.4
22.6
18.2
14.7
12.1
9.76
timer has a maximum value of 210ns over temp. On the
other hand, delays associated with turning off the power
switch dictate the minimum on time t ON(MIN) before the
switch can be turned off; t ON(MIN) has a maximum value
of 150ns over temp. The minimum and maximum duty
cycles that can be achieved taking minimum on and off
times into account 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 (210ns). These equations show
that duty cycle range increases when switching frequency
is decreased.
2.2 8.06
Figure 1. Switching Frequency vs. R T Value
Operating Frequency Tradeoffs
Selection of the operating frequency is a tradeoff between
ef?ciency, component size, minimum dropout voltage, and
maximum input voltage. The advantage of high frequency
A good choice of switching frequency should allow adequate
input voltage range (see Input Voltage Range section) and
keep the inductor and capacitor values small.
Input Voltage Range
The minimum input voltage is determined by either the
LT3682’s minimum operating voltage of ~3.6V (V BD > 3V)
or by its maximum duty cycle (see equation in Operating
3682f
11
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