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参数资料
| 型号： | LT3685IDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2A 10DFN |
| 标准包装： | 121 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.79 V ~ 20 V |
| 输入电压： | 3.6 V ~ 36 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 200kHz ~ 2.4MHz |
| 电流 - 输出： | 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： | 管件 |
| 供应商设备封装： | 10-DFN（3x3） |
| 产品目录页面： | 1332 (CN2011-ZH PDF) |
LT3685
APPLICATIONS INFORMATION
R 1 = R 2 ? OUT – 1 ?
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
? V ?
? 0 . 79 V ?
Reference designators refer to the Block Diagram.
Setting the Switching Frequency
The LT3685 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.4MHz
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.
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 next section, lower frequency allows a lower dropout
voltage. The reason input voltage range depends on the
switching frequency is because the LT3685 switch has ?nite
minimum on and off times. The switch can turn on for a
minimum of ~150ns and turn off for a minimum of ~150ns.
Typical minimum on time at 25°C is 80ns. 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
SWITCHING FREQUENCY (MHz)
0.2
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
2.2
2.4
R T VALUE (kΩ)
187
121
88.7
68.1
56.2
46.4
40.2
34
29.4
23.7
19.1
16.2
13.3
11.5
9.76
8.66
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 LT3685 applications
depends on switching frequency, the Absolute Maximum
Ratings of the V IN and BOOST pins, and the operating
mode.
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
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:
The LT3685 can operate from input voltages up to 38V,
and safely withstand input voltages up 60V. Note that
while V IN > 38V (typical), the LT3685 will stop switching,
allowing the output to fall out of regulation.
While the output is in start-up, short-circuit, or other
overload conditions, the switching frequency should be
chosen according to the following discussion.
For safe operation at inputs up to 60V the switching fre-
quency must be set low enough to satisfy V IN(MAX) ≥ 40V
according to the following equation. If lower V IN(MAX) is
f SW ( MAX ) =
V D + V OUT
t ON ( MIN ) ( V D + V IN – V SW )
desired, this equation can be used directly.
3685fb
9
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3685IDD-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:36V, 2A, 2.4MHz Step-Down Switching Regulator |
| LT3685IMSE#PBF | 功能描述:IC REG BUCK ADJ 2A 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT3685IMSE#PBF | 制造商:Linear Technology 功能描述:DC-DC CONVERTER BUCK 2.4MHZ 制造商:Linear Technology 功能描述:DC-DC CONVERTER, BUCK, 2.4MHZ, MSOP-10 |
| LT3685IMSE#TRPBF | 功能描述:IC REG BUCK ADJ 2A 10MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT3685IMSEPBF | 制造商:Linear Technology 功能描述:36V 2A 2.4MHz Switch. Regulator MSOP10EP |
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