参数资料
| 型号： | LT1676IS8#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 7/16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 ~ 51 V |
| 输入电压： | 7.4 V ~ 60 V |
| PWM 型： | 电流模式，混合 |
| 频率 - 开关： | 100kHz |
| 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 |
LT1676
OPERATIO
L = ? OUT ? ? IN OUT ?
Please refer to the High dV/dt Mode Timing Diagram. A
typical oscillator cycle is as follows: The logic section first
generates an SWDR signal that powers up the current
comparator and allows it time to settle. About 1 μ s later, the
SWON signal is asserted and the BOOST signal is pulsed
for a few hundred nanoseconds. After a short delay, the
V SW pin slews rapidly to V IN . Later, after the peak switch
current indicated by the control voltage V C has been
reached (current mode control), the SWON and SWDR
signals are turned off, and SWOFF is pulsed for several
hundred nanoseconds. The use of an explicit turn-off
device, i.e., Q5, improves turn-off response time and thus
aids both controllability and efficiency.
The system as previously described handles heavy loads
(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
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 LT1676 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:
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
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 LT1676 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.
? V ? ? V – V ?
? f ? I PK ? ? V IN ?
For example, substituting 48V, 5V, 200mA and 100kHz
respectively for V IN , V OUT , I PK and f yields a value of about
220 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 50V for 5V OUT , the user should choose an
inductance value based on the maximum input voltage.
7
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| LT1677CN8 | 功能描述:IC OPAMP R-R I/O SGL LN 8DIP RoHS:否 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 标准包装:50 系列:- 放大器类型:通用 电路数:2 输出类型:满摆幅 转换速率:1.8 V/µs 增益带宽积:6.5MHz -3db带宽:4.5MHz 电流 - 输入偏压:5nA 电压 - 输入偏移:100µV 电流 - 电源:65µA 电流 - 输出 / 通道:35mA 电压 - 电源，单路/双路(±):1.8 V ~ 5.25 V，±0.9 V ~ 2.625 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
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