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参数资料
| 型号： | LTC1877IMS8#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.5 A SWITCHING REGULATOR, 605 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | LEAD FREE, PLASTIC, MSOP-8 |
| 文件页数： | 16/16页 |
| 文件大小： | 234K |
| 代理商： | LTC1877IMS8#TRPBF |
LTC1877
9
1877fa
APPLICATIONS INFORMATION
Accepting larger values of ΔIL allows the use of low in-
ductance, but results in higher output voltage ripple and
greater core losses. A reasonable starting point for setting
ripple current is ΔIL = 0.4(IMAX).
The inductor value also has an effect on Burst Mode opera-
tion. The transition to low current operation begins when
the inductor current peaks fall to approximately 250mA.
Lower inductor values (higher ΔIL) will cause this to occur
at lower load currents, which can cause a dip in efciency
in the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to increase.
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efciency converters generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of more expensive ferrite, molypermalloy,
or Kool Mμ cores. Actual core loss is independent of core
size for a xed inductor value, but it is very dependent
on inductance selected. As inductance increases, core
losses go down. Unfortunately, increased inductance
requires more turns of wire and therefore copper losses
will increase.
Ferrite designs have very low core losses and are pre-
ferred at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates hard, which means that
inductance collapses abruptly when the peak design current
is exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
Kool Mμ (from Magnetics, Inc.) is a very good, low loss core
material for toroids with a soft saturation characteristic.
Molypermalloy is slightly more efcient at high (>200kHz)
switching frequencies but quite a bit more expensive. To-
roids are very space efcient, especially when you can use
several layers of wire, while inductors wound on bobbins
are generally easier to surface mount. New designs for
surface mount inductors are available from Coiltronics,
Coilcraft, Dale and Sumida.
CIN and COUT Selection
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle VOUT/VIN. To prevent large
voltage transients, a low ESR input capacitor sized for the
maximum RMS current must be used. The maximum RMS
capacitor current is given by:
CI
VV
V
IN
OMAX
OUT
IN
OUT
IN
required IRMS
()
[]12/
This formula has a maximum at VIN = 2VOUT, where IRMS
= IOUT/2. This simple worst-case condition is commonly
used for design because even signicant deviations do
not offer much relief. Note the capacitor manufacturer’s
ripple current ratings are often based on 2000 hours of
life. This 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. Always consult
the manufacturer if there is any question.
The selection of COUT is driven by the required effective
series resistance (ESR). Typically, once the ESR require-
ment is satised, the capacitance is adequate for ltering.
The output ripple ΔVOUT is determined by:
Δ Δ
+
V
I ESR
fC
OUT
L
OUT
1
8
where f = operating frequency, COUT = output capacitance
and ΔIL = ripple current in the inductor. The output ripple
is highest at maximum input voltage since ΔIL increases
with input voltage. For the LTC1877, the general rule for
proper operation is:
COUT required ESR < 0.25Ω
The choice of using a smaller output capacitance increases
the output ripple voltage due to the frequency dependent
term but can be compensated for by using capacitor(s) of
very low ESR to maintain low ripple voltage. The ITH pin
compensation components can be optimized to provide
stable high performance transient response regardless of
the output capacitor selected.
ESR is a direct function of the volume of the capacitor.
Manufacturers such as Taiyo Yuden, AVX, Sprague, Kemet
and Sanyo should be considered for high performance ca-
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC1878EMS8 | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1878EMS8#PBF | 功能描述:IC REG BUCK SYNC ADJ 0.6A 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 |
| LTC1878EMS8#TR | 功能描述:IC REG BUCK SYNC ADJ 0.6A 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1878EMS8#TRPBF | 功能描述:IC REG BUCK SYNC ADJ 0.6A 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:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1878EMS8PBF | 制造商:Linear Technology 功能描述: 制造商:Linear Technology 功能描述:DC-DC Converter Step-Down 2.65-6V MSOP8 |
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