參數(shù)資料
型號(hào)： LT1977EFE
廠(chǎng)商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： High Voltage 1.5A, 500kHz Step-Down Switching Regulator with 100uA Quiescent Current
中文描述： 3.5 A SWITCHING REGULATOR, 575 kHz SWITCHING FREQ-MAX, PDSO16
封裝： 4.4 MM, PLASTIC, TSSOP-16
文件頁(yè)數(shù)： 15/24頁(yè)
文件大?。?/td> 288K
代理商： LT1977EFE
LT1977
15
1977f
APPLICATIOU
low value such that the current doesn’t continue to ratchet
higher. When the FB pin voltage is abnormally low thereby
indicating some sort of short-circuit condition, the oscil-
lator frequency will be reduced. Oscillator frequency is
reduced by a factor of 4 when the FB pin voltage is below
0.4V and increases linearly to its typical value of 500kHz at
a FB voltage of 0.95V (see Typical Performance Character-
istics). In addition, if the current in the switch exceeds 1.5
I
PK
current demanded by the V
C
pin, the LT1977 will skip
the next on cycle effectively reducing the oscillator fre-
quency by a factor of 2. These oscillator frequency reduc-
tions during short-circuit conditions allow the LT1977 to
maintain current control.
W
U
U
SOFT-START
For applications where [V
IN
/(V
OUT
+ V
F
)] ratios > 10 or
large input surge currents can’t be tolerated, the LT1977
soft-start feature should be used to control the output
capacitor charge rate during start-up, or during recovery
from an output short circuit thereby adding additional
control over peak inductor current. The soft-start function
limits the switch current via the V
C
pin to maintain a
constant voltage ramp rate (dV/dt) at the output capacitor.
A capacitor (C1 in Figure 2) from the C
SS
pin to the
regulated output voltage determines the output voltage
ramp rate. When the current through the C
SS
capacitor
exceeds the C
SS
threshold (I
CSS
), the voltage ramp of the
output capacitor is limited by reducing the V
C
pin voltage.
The C
SS
threshold is proportional to the FB voltage (see
Typical Performance Characteristics) and is defeated for
FB voltages greater than 0.9V (typical). The output dV/dt
can be approximated by:
dV
dt
I
C
CSS
SS
=
but actual values will vary due to start-up load conditions,
compensation values and output capacitor selection.
Burst Mode OPERATION
T
o enhance efficiency at light loads, the LT1977 automati-
cally switches to Burst Mode operation (see Typical
Performance Characteristics) which keeps the output
Figure 4. V
OUT
dV/dt
V
1V/DIV
V
IN
= 12V
V
OUT
= 3.3V
1ms/DIV
1977 F04
C
CSS
= 1000pF
C
CSS
= 0.01
μ
F
C
CSS
= 0.1
μ
F
capacitor charged to the proper voltage while minimizing
the input quiescent current. During Burst Mode opera-
tion, the LT1977 delivers short bursts of current to the
output capacitor followed by sleep periods where the
output power is delivered to the load by the output
capacitor. In addition, V
IN
and BIAS quiescent currents
are reduced to typically 45
μ
A and 125
μ
A respectively
during the sleep time. As the load current decreases
towards a no load condition, the percentage of time that
the LT1977 operates in sleep mode increases and the
average input current is greatly reduced resulting in
higher efficiency.
The minimum average input current depends on the V
IN
to
V
OUT
ratio, V
C
frequency compensation, feedback divider
network and Schottky diode leakage. It can be approxi-
mated by the following equation:
I
I
I
V
V
I
I
I
IN AVG
(
VINS
SHDN
OUT
IN
BIASS
FB
S
)
+
+
+
( )
η
+
(
)
where:
I
VINS
= input pin current in sleep mode
V
OUT
= output voltage
V
IN
=
input voltage
I
BIASS
= BIAS pin current in sleep mode
I
FB
= feedback network current
I
S
= catch diode reverse leakage at V
OUT
η
= low current efficiency (non Burst Mode operation)
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LT1977EFE#PBF 功能描述:IC REG BUCK ADJ 1.5A 16TSSOP RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類(lèi)型:降壓（降壓） 輸出類(lèi)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(kāi)關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁(yè)面:1032 (CN2011-ZH PDF) 其它名稱(chēng):296-25628-2
LT1977EFE#TR 功能描述:IC REG BUCK ADJ 1.5A 16TSSOP RoHS:否 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 設(shè)計(jì)資源:Design Support Tool 標(biāo)準(zhǔn)包裝:1 系列:- 類(lèi)型:升壓（升壓） 輸出類(lèi)型:固定 輸出數(shù):1 輸出電壓:3V 輸入電壓:0.75 V ~ 2 V PWM 型:- 頻率 - 開(kāi)關(guān):- 電流 - 輸出:100mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:SOT-23-5 細(xì)型，TSOT-23-5 包裝:剪切帶 (CT) 供應(yīng)商設(shè)備封裝:TSOT-23-5 其它名稱(chēng):AS1323-BTTT-30CT
LT1977EFE#TRPBF 功能描述:IC REG BUCK ADJ 1.5A 16TSSOP RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 設(shè)計(jì)資源:Design Support Tool 標(biāo)準(zhǔn)包裝:1 系列:- 類(lèi)型:升壓（升壓） 輸出類(lèi)型:固定 輸出數(shù):1 輸出電壓:3V 輸入電壓:0.75 V ~ 2 V PWM 型:- 頻率 - 開(kāi)關(guān):- 電流 - 輸出:100mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:SOT-23-5 細(xì)型，TSOT-23-5 包裝:剪切帶 (CT) 供應(yīng)商設(shè)備封裝:TSOT-23-5 其它名稱(chēng):AS1323-BTTT-30CT
LT1977EFEPBF 制造商:Linear Technology 功能描述:LT1977 adj PWM 1.5A SD dc-dc converter
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