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参数资料
| 型号： | LT3681EDE |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 4.4 A SWITCHING REGULATOR, 3100 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封装： | 4 X 3 MM, PLASTIC, DFN-14 |
| 文件页数： | 3/24页 |
| 文件大小： | 367K |
| 代理商： | LT3681EDE |
LT3681
11
3681f
Of course, such a simple design guide will not always re-
sult in the optimum inductor for your application. A larger
value inductor provides a slightly higher maximum load
current and will reduce the output voltage ripple. If your
load is lower than 2A, then you can decrease the value of
the inductor and operate with higher ripple current. This
allows you to use a physically smaller inductor, or one
with a lower DCR resulting in higher efciency. There are
several graphs in the Typical Performance Characteristics
section of this data sheet that show the maximum load
current as a function of input voltage and inductor value
for several popular output voltages. Low inductance may
result in discontinuous mode operation, which is okay
but further reduces maximum load current. For details of
maximum output current and discontinuous mode opera-
tion, see Linear Technology Application Note 44. Finally,
for duty cycles greater than 50% (VOUT/VIN > 0.5), there
is a minimum inductance required to avoid subharmonic
oscillations. See Application Note 19.
Input Capacitor
Bypass the input of the LT3681 circuit with a ceramic capaci-
tor of X7R or X5R type. Y5V types have poor performance
over temperature and applied voltage, and should not be
used. A 4.7F to 10F ceramic capacitor is adequate to
bypass the LT3681 and will easily handle the ripple current.
Note that larger input capacitance is required when a lower
switching frequency is used. If the input power source has
high impedance, or there is signicant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage
ripple at the LT3681 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7F capacitor is capable of this task, but only if it is
placed close to the LT3681 and the catch diode (see the
PCB Layout section). A second precaution regarding the
ceramic input capacitor concerns the maximum input
voltage rating of the LT3681. A ceramic input capacitor
combined with trace or cable inductance forms a high
quality (under damped) tank circuit. If the LT3681 circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT3681’s
voltage rating. This situation is easily avoided (see the Hot
Plugging Safely section).
For space sensitive applications, a 2.2F ceramic capaci-
tor can be used for local bypassing of the LT3681 input.
However, the lower input capacitance will result in in-
creased input current ripple and input voltage ripple, and
may couple noise into other circuitry. Also, the increased
voltage ripple will raise the minimum operating voltage
of the LT3681 to ~3.7V.
Output Capacitor and Output Ripple
The output capacitor has two essential functions. Along
with the inductor, it lters the square wave generated by the
LT3681 to produce the DC output. In this role it determines
the output ripple, and low impedance at the switching
frequency is important. The second function is to store
energy in order to satisfy transient loads and stabilize the
LT3681’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
C
Vf
OUT
OUT SW
=
100
where fSW is in MHz, and COUT is the recommended
output capacitance in F. Use X5R or X7R types. This
choice will provide low output ripple and good transient
response. Transient performance can be improved with
a higher value capacitor if the compensation network is
also adjusted to maintain the loop bandwidth. A lower
value of output capacitor can be used to save space and
cost but transient performance will suffer. See the Fre-
quency Compensation section to choose an appropriate
compensation network.
APPLICATIONS INFORMATION
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相关代理商/技术参数 |
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| LT3681EDE#PBF | 功能描述:IC REG BUCK ADJ 2A 14DFN 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 |
| LT3681EDE#PBF | 制造商:Linear Technology 功能描述:IC STEP-DOWN REGULATOR DFN-14 |
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| LT3681EDEPBF | 制造商:Linear Technology 功能描述:36V 2.8MHz Step-Down Regulator LT3681 |
| LT3682 | 制造商:LINER 制造商全称:Linear Technology 功能描述:42V, 750mA Step-Down Regulator with 2.5μA |
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