参数资料
| 型号： | LT1776IS8#TR |
| 厂商： | Linear Technology |
| 文件页数： | 8/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 0.7A 8SOIC |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.24 V ~ 34 V |
| 输入电压： | 7.4 V ~ 40 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 200kHz |
| 电流 - 输出： | 700mA |
| 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： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
LT1776
OPERATIO
L = ? OUT ? ? IN OUT ?
Thesystemaspreviouslydescribedhandlesheavyloads
(continuous mode) at good efficiency, but it is actually
counterproductive for light loads. The method of jam-
ming charge into the PNP bases makes it difficult to turn
them off rapidly and achieve the very short switch ON
times required by light loads in discontinuous mode.
Furthermore, the high leading edge dV/dt rate similarly
adversely affects light load controllability.
The solution is to employ a “boost comparator” whose
inputs are the V C control voltage and a fixed internal
threshold reference, V TH . (Remember that in a current
mode switching topology, the V C voltage determines the
peak switch current.) When the V C signal is above V TH , the
previously described “high dV/dt” action is performed.
When the V C signal is below V TH , the boost pulses are
absent, as can be seen in the Low dV/dt Mode Timing
Diagram. Now the DC current, activated by the SWON
APPLICATIO N S I N FOR M ATIO N
Selecting a Power Inductor
There are several parameters to consider when selecting
a power inductor. These include inductance value, peak
current rating (to avoid core saturation), DC resistance,
construction type, physical size, and of course, cost.
In a typical application, proper inductance value is dictated
by matching the discontinuous/continuous crossover point
with the LT1776 internal low-to-high dV/dt threshold. This
is the best compromise between maintaining control with
light loads while maintaining good efficiency with heavy
loads. The fixed internal dV/dt threshold has a nominal
value of 1.4V, which referred to the V C pin threshold and
control voltage to switch transconductance, corresponds
to a peak current of about 200mA. Standard buck con-
verter theory yields the following expression for induc-
tance at the discontinuous/continuous crossover:
? V ? ? V – V ?
? f ? I PK ? ? V IN ?
signal alone, drives Q4 and this transistor drives Q1 by
itself. The absence of a boost pulse, plus the lack of a
second NPN driver, result in a much lower slew rate which
aids light load controllability.
A further aid to overall efficiency is provided by the
specialized bias regulator circuit, which has a pair of
inputs, V IN and V CC . The V CC pin is normally connected to
the switching supply output. During start-up conditions,
the LT1776 powers itself directly from V IN . However, after
the switching supply output voltage reaches about 2.9V,
the bias regulator uses this supply as its input. Previous
generation buck controller ICs without this provision
typically required hundreds of milliwatts of quiescent
power when operating at high input voltage. This both
degraded efficiency and limited available output current
due to internal heating.
For example, substituting 40V, 5V, 200mA and 200kHz
respectively for V IN , V OUT , I PK and f yields a value of about
100 μ H. Note that the left half of this expression is indepen-
dent of input voltage while the right half is only a weak
function of V IN when V IN is much greater than V OUT . This
means that a single inductor value will work well over a
range of “high” input voltage. And although a progres-
sively smaller inductor is suggested as V IN begins to
approach V OUT , note that the much higher ON duty cycles
under these conditions are much more forgiving with
respect to controllability and efficiency issues. Therefore
when a wide input voltage range must be accommodated,
say 10V to 40V for 5V OUT , the user should choose an
inductance value based on the maximum input voltage.
Once the inductance value is decided, inductor peak
current rating and resistance need to be considered. Here,
the inductor peak current rating refers to the onset of
saturation in the core material, although manufacturers
sometimes specify a “peak current rating” which is de-
rived from a worst-case combination of core saturation
and self-heating effects. Inductor winding resistance alone
8
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1777 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Low Noise Step-Down Switching Regulator |
| LT1777C | 制造商:LINER 制造商全称:Linear Technology 功能描述:Low Noise Step-Down Switching Regulator |
| LT1777CS | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC 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 |
| LT1777CS#PBF | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC 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 |
| LT1777CS#TR | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC 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 |
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