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| 型号： | LT3645EMSE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 300K |
| 描述： | IC REG DL BUCK/LINEAR 12-MSOP |
| 标准包装： | 2,500 |
| 拓扑： | 降压（降压）（1），线性（LDO）（1） |
| 功能： | 车载 |
| 输出数： | 2 |
| 频率 - 开关： | 750kHz |
| 电压/电流 - 输出 1： | 0.8 V ~ 16 V，500mA |
| 电压/电流 - 输出 2： | 0.8 V ~ 8 V，200mA |
| 带 LED 驱动器： | 无 |
| 带监控器： | 无 |
| 带序列发生器： | 无 |
| 电源电压： | 3.6 V ~ 36 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 12-TSSOP （0.118"，3.00mm 宽）裸露焊盘 |
| 供应商设备封装： | 12-MSOP，裸露焊盘 |
| 包装： | 带卷 (TR) |
LT3645
12
3645f
APPLICATIONS INFORMATION
Output Capacitor
The output capacitor has two essential functions. Along
with the inductor, it lters the square wave generated
by the LT3645 to produce the DC output. In this role it
determines the output ripple so low impedance at the
switching frequency is important. The second function
is to store energy in order to satisfy transient loads and
stabilize the LT3645s control loop.
Ceramic capacitors have very low equivalent series re-
sistance (ESR) and provide the best ripple performance.
A good value is:
C
OUT
= 26.4/(V
OUT
" ?
where f is the switching frequency in MHz and C
OUT
is in
糉. This choice will provide low output ripple and good
transient response. C
OUT
= 10糉 is a good choice for
output voltages above 2.5V. For lower output voltages
use 22糉 or higher.
Transient performance can be improved with a high value
capacitor, but a phase lead capacitor across the feedback
resistor R1 may be required to get the full bene t (see the
Compensation section). Using a small output capacitor
results in an increased loop crossover frequency.
Use X5R or X7R types and keep in mind that a ceramic
capacitor biased with V
OUT
will have less than its nominal
capacitance. High performance electrolytic capacitors can
be used for the output capacitor. Low ESR is important, so
choose one that is intended for use in switching regulators.
The ESR should be speci ed by the supplier and should be
0.1?or less. Such a capacitor will be larger than a ceramic
capacitor and will have a larger capacitance, because the
capacitor must be large to achieve low ESR.
Table 2 lists several capacitor vendors.
Table 2. Capacitor Vendors
AVX
www.avxcorp.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay Siliconix
www.vishay.com
TDK
www.tdk.com
BOOST Pin Considerations
The external capacitor C2 and an internal Schottky diode
connected between the V
CC2
and BOOST pins form a
charge pump circuit which is used to generate a boost
voltage that is higher than the input voltage (V
IN
). In most
application circuits where the duty cycle is less than 50%,
use C2 = 0.1糉. If the duty cycle is higher than 50% then
use C2 = 0.22糉.
The BOOST pin must be at least 2.2V above the SW pin
to fully saturate the NPN power switch (Q1). The forward
drop of the internal Schottky diode is 0.8V. This means
that V
CC2
must be tied to a supply greater than 2.6V.
V
CC2
may be tied to a supply between 2.2V and 2.6V if an
external Schottky diode (such as a BAS70) is connected
from V
CC2
(anode) to BOOST (cathode).
If no voltage supply greater than 2.6V is available, then
an external boost Schottky diode can be tied from the
V
IN
pin (anode) to the BOOST pin (cathode) as shown in
Figure 3. In this con guration, the BOOST capacitor will be
charged to approximately the V
IN
voltage, and will change
if V
IN
changes. In this con guration the maximum operat-
ing V
IN
is 25V, because when V
IN
= 25V, then when the
power switch Q1 turns on, V
SW
~ 25V, and since the boost
capacitor is charged to 25V, the BOOST pin will be at 50V.
This connection is not as ef cient as the others because
the BOOST pin current comes from a higher voltage.
The minimum operating voltage of an LT3645 application
is limited by the undervoltage lockout (~3.4V) and by
the maximum duty cycle as outlined above. For proper
startup, the minimum input voltage is also limited by the
Figure 3.
V
IN
BOOST
GND
SW
V
IN
LT3645
D2
3645 F03
V
OUT
C3
V
BOOST
V
SW
V
IN
MAX V
BOOST
2V
IN
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| LT3645EUD#PBF | 功能描述:IC REG DL BUCK/LINEAR 16-QFN 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:* |
| LT3645EUD#TRPBF | 功能描述:IC REG DL BUCK/LINEAR 16-QFN 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:* |
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| LT3645HMSE#TRPBF | 功能描述:IC REG DL BUCK/LINEAR 12-MSOP 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:* |
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