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參數(shù)資料
| 型號： | LT1776IS8#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1 A SWITCHING REGULATOR, 230 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SO-8 |
| 文件頁數(shù)： | 2/20頁 |
| 文件大?。?/td> | 224K |
| 代理商： | LT1776IS8#TR |
10
LT1776
Input Voltage vs Operating Frequency Considerations
The absolute maximum input supply voltage for the LT1776
is specified at 60V. This is based solely on internal semi-
conductor junction breakdown effects. Due to internal
power dissipation, the actual maximum VIN achievable in
a particular application may be less than this.
A detailed theoretical basis for estimating internal power
loss is given in the section, Thermal Considerations. Note
that AC switching loss is proportional to both operating
frequency and output current. The majority of AC switch-
ing loss is also proportional to the square of input voltage.
For example, while the combination of VIN = 40V, VOUT =
5V at 500mA and fOSC = 200kHz may be easily achievable,
simultaneously raising VIN to 60V and fOSC to 400kHz is
not possible. Nevertheless, input voltage
transients up to
60V can usually be accommodated, assuming the result-
ing increase in internal dissipation is of insufficient time
duration to raise die temperature significantly.
A second consideration is controllability. A potential limi-
tation occurs with a high step-down ratio of VIN to VOUT,
as this requires a correspondingly narrow minimum switch
ON time. An approximate expression for this (assuming
continuous mode operation) is given as follows:
M
VV
Vf
ON
OUT
F
IN OSC
in t
=
+
()
where:
VIN = input voltage
VOUT = output voltage
VF = Schottky diode forward drop
fOSC = switching frequency
It is important to understand the nature of minimum
switch ON time as given in the data sheet. This test is
intended to mimic behavior under short-circuit condi-
tions. It is performed with the VC control voltage at its
clamp level (VCL) and uses a fixed resistive load from VSW
to ground for simplicity. The resulting ON time behavior is
overconservative as a general operating design value for
two reasons. First, actual power supply application cir-
cuits present an inductive load to the VSW node. The
APPLICATIONS INFORMATION
WU
U
resulting ramping current behavior helps overdrive the
current comparator (current mode switching) and reduce
its propagation delay, hastening output switch turnoff.
Second, and more importantly, actual power supply op-
eration involves a feedback amplifier that adjusts the VC
node control voltage to maintain proper output voltage. As
progressively shorter ON times are required, the feedback
loop acts to reduce VC, and the resulting overdrive further
reduces the propagation delay in the current comparator.
A suggested worst-case limit for minimum switch ON time
in actual operation is 350ns.
A potential controllability problem arises if the LT1776 is
called upon to produce an ON time shorter than its ability.
Feedback loop action will lower then reduce the VC control
voltage to the point where some sort of cycle-skipping or
odd/even cycle behavior is exhibited.
In summary:
1. Be aware that the simultaneous requirements of high
VIN, high IOUT and high fOSC may not be achievable in
practice due to internal dissipation. The Thermal Con-
siderations section offers a basis to estimate internal
power. In questionable cases a prototype supply should
be built and exercised to verify acceptable operation.
2. The simultaneous requirements of high VIN, low VOUT
and high fOSC can result in an unacceptably short
minimum switch ON time. Cycle skipping and/or odd/
even cycle behavior will result although correct output
voltage is usually maintained.
Minimum Load Considerations
As discussed previously, a lightly loaded LT1776 with VC
pin control voltage below the boost threshold will operate
in low dV/dt mode. This affords greater controllability at
light loads, as minimum tON requirements are relaxed.
However, some users may be indifferent to pulse skipping
behavior, but instead may be concerned with maintaining
maximum possible efficiency at light loads. This require-
ment can be satisfied by forcing the part into Burst Mode
TM
operation. The use of an external comparator whose
Burst Mode is a trademark of Linear Technology Corporation.
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相關代理商/技術參數(shù) |
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| LT1777 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Low Noise Step-Down Switching Regulator |
| LT1777C | 制造商:LINER 制造商全稱: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 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關:600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應商設備封裝:8-SOIC |
| LT1777CS#PBF | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關:2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應商設備封裝:6-SON（1.45x1） 產品目錄頁面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
| LT1777CS#TR | 功能描述:IC REG BUCK ADJ 0.7A 16SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調式 輸出數(shù):1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關:600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應商設備封裝:8-SOIC |
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