參數(shù)資料
型號(hào)： LT3689EMSE-5#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16
封裝： LEAD FREE, PLASTIC, MSOP-16
文件頁(yè)數(shù)： 14/32頁(yè)
文件大?。?/td> 2188K
代理商： LT3689EMSE-5#TRPBF
LT3689/LT3689-5
21
3689fd
Another way to lower the start-up voltage is by using a
resistor divider on the EN/UVLO pin (see the Shutdown
and Undervoltage Lockout section). A resistor divider on
EN/UVLO pin programs the turn-on threshold to slightly
higher than the minimum VINvoltagerequiredtorunatfull
load. Below the EN/UVLO high voltage, the part will stay
shut off and the output cap will remain discharged during
the worse case slow VIN ramp. When the EN/UVLO pin
crosses the EN/UVLO high threshold, the part will turn on
and the empty output capacitor will provide enough load
to bring the output voltage in regulation. This technique
significantly lowers the start-up voltage of the circuit. The
plot in Figure 7 depicts the minimum load required to start
and run (as a function of input voltage). It also depicts the
benefit of programming the EN/UVLO threshold to lower
the start-up voltage at low load currents. At light loads, the
inductor current becomes discontinuous and the effective
dutycyclecanbeveryhigh.Thisreducestheminimuminput
voltagetoapproximately300mVaboveVOUT.Athigherload
currents, the inductor current is continuous and the duty
cycle is limited by the maximum duty cycle of the LT3689,
requiring a higher input voltage to maintain regulation.
Soft-Start
The LT3689 has an internal soft-start that gradually ramps
uptheswitchcurrentlimitfromabout100mAtotheswitch’s
maximum current limit in typical value of 150s, as shown
in Figure 8. This feature limits the inrush current during
start-upandpreventstheswitchcurrentfromspikingwhen
the EN/UVLO pin crosses the UVLO threshold. A soft-start
sequence is also initiated right after a VIN overvoltage/
undervoltage lockout, or thermal shutdown fault in order
to prevent the switch current from suddenly jumping to
its maximum current limit.
APPLICATIONS INFORMATION
Figure 7. LT3689 Minimum VIN to Start and Run vs Load
Figure 8. Internal Soft-Start
20s/DIV
VOUT
2V/DIV
VIN = 12V
VOUT = 5V
f = 2MHz
CIN = 1F CERAMIC + 100F ELECTROLYTIC
IVIN
0.2A/DIV
IL
0.5A/DIV
3689 F08
LOAD (mA)
1
7.0
V IN
(V
)
7.5
10
100
1000
6.5
6.0
5.5
5.0
8.0
3589 F07a
TO START:
EN/UVLO TIED TO VIN
TO RUN
VOUT = 5V
L = 8.2H
fSW = 800KHz
TA = 25°C
TO START: EN/UVLO HIGH
THRESHOLD = 6.15V
LOAD (mA)
1
5.0
V IN
(V
)
5.5
10
100
1000
4.5
4.0
3.5
3.0
6.0
3589 F07b
TO START:
EN/UVLO TIED TO VIN
TO RUN
VOUT = 3.3V
L = 8.2H
fSW = 800KHz
TA = 25°C
TO START: EN/UVLO HIGH
THRESHOLD = 4.85V
相關(guān)PDF資料
PDF描述
LT3689EUD-5#TRPBF 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PQCC16
LT3689EMSE-5#PBF 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16
LT3689IUD-5#TRPBF 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PQCC16
LT3689IMSE-5#TRPBF 1.95 A SWITCHING REGULATOR, 2160 kHz SWITCHING FREQ-MAX, PDSO16
LT3692IUH#TRPBF 5.8 A DUAL SWITCHING CONTROLLER, 2750 kHz SWITCHING FREQ-MAX, PQCC32
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LT3689EMSE-TRPBF 制造商:LINER 制造商全稱:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer
LT3689EUD#PBF 功能描述:IC REG BUCK ADJ 0.7A 16QFN RoHS:是 類別: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:- 類型:升壓（升壓） 輸出類型: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:AS1323-BTTT-30CT
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LT3689EUD-5#PBF 功能描述:IC REG BUCK 5V 0.7A 16QFN RoHS:是 類別: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:2,500 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，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開(kāi)關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤
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