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| 型号： | LTC3631EDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 0.1A 8DFN |
| 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： | 0.8 V ~ 45 V |
| 输入电压： | 4.5 V ~ 45 V |
| PWM 型： | Burst Mode? |
| 电流 - 输出： | 100mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-WFDFN 裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 8-DFN-EP（3x3） |
| 产品目录页面： | 1335 (CN2011-ZH PDF) |
LTC3631
APPLICATIONS INFORMATION
? I ? 4 ? 10 – 6 V
L IN
L IN
C IN
This formula has a maximum at V IN = 2V OUT , where
I RMS = I OUT /2. This simple worst-case condition is com-
monly used for design because even significant deviations
do not offer much relief. Note that ripple current ratings
from capacitor manufacturers are often based only on
2000 hours of life which makes it advisable to further
derate the capacitor, or choose a capacitor rated at a
higher temperature than required. Several capacitors may
also be paralleled to meet size or height requirements in
the design.
The output capacitor, C OUT , filters the inductor’s ripple
current and stores energy to satisfy the load current when
the LTC3631 is in sleep. The output ripple has a lower limit
of V OUT /160 due to the 5mV typical hysteresis of the feed-
back comparator. The time delay of the comparator adds
an additional ripple voltage that is a function of the load
current. During this delay time, the LTC3631 continues to
switch and supply current to the output. The output ripple
can be approximated by:
Δ V OUT ≈ ? PEAK – I LOAD ? + OUT
? 2 ? C OUT 160
The output ripple is a maximum at no load and approaches
lower limit of V OUT /160 at full load. Choose the output
capacitor C OUT to limit the output voltage ripple at mini-
mum load current.
The value of the output capacitor must be large enough
to accept the energy stored in the inductor without a large
change in output voltage. Setting this voltage step equal
to 1% of the output voltage, the output capacitor must be:
? I ? 2
C OUT > 50 ? L ? ? PEAK ?
? V OUT ?
Typically, a capacitor that satisfies the voltage ripple re-
quirement is adequate to filter the inductor ripple. To avoid
overheating, the output capacitor must also be sized to
handle the ripple current generated by the inductor. The
worst-case ripple current in the output capacitor is given
by I RMS = I PEAK /2. Multiple capacitors placed in parallel
may be needed to meet the ESR and RMS current handling
requirements.
Tantalum, special polymer, aluminum electrolytic, and
ceramic capacitors are all available in surface mount
packages. Special polymer capacitors offer very low ESR
but have lower capacitance density than other types.
Tantalum capacitors have the highest capacitance density
but it is important only to use types that have been surge
tested for use in switching power supplies. Aluminum
electrolytic capacitors have significantly higher ESR but
can be used in cost-sensitive applications provided that
consideration is given to ripple current ratings and long-
term reliability. Ceramic capacitors have excellent low ESR
characteristics but can have high voltage coefficient and
audible piezoelectric effects. The high quality factor (Q)
of ceramic capacitors in series with trace inductance can
also lead to significant ringing.
Using Ceramic Input and Output Capacitors
Higher value, lower cost ceramic capacitors are now be-
coming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input and
the power is supplied by a wall adapter through long wires,
a load step at the output can induce ringing at the input,
V IN . At best, this ringing can couple to the output and be
mistaken as loop instability. At worst, a sudden inrush
of current through the long wires can potentially cause a
voltage spike at V IN large enough to damage the LTC3631.
For applications with inductive source impedance, such
as a long wire, a series RC network may be required in
parallel with C IN to dampen the ringing of the input supply.
Figure 5 shows this circuit and the typical values required
to dampen the ringing.
LTC3631
V IN
R=
3631 F05
4 ? C IN C IN
Figure 5. Series RC to Reduce V IN Ringing
3631fe
12
For more information www.linear.com/LTC3631
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| LTC3631EMS8E#PBF | 功能描述:IC REG BUCK SYNC ADJ 0.1A 8MSOP 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 |
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