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參數(shù)資料
| 型號(hào)： | LTC3879IUD#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PQCC16 |
| 封裝： | 3 X 3 MM, LEAD FREE, PLASTIC, MO-220WEED-4, QFN-16 |
| 文件頁(yè)數(shù)： | 3/28頁(yè) |
| 文件大?。?/td> | 302K |
| 代理商： | LTC3879IUD#PBF |
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LTC3879
11
3879f
APPLICATIONS INFORMATION
The basic LTC3879 application circuit is shown on the rst
page of this data sheet. External component selection is
largely determined by maximum load current and begins
with the selection of sense resistance and power MOSFET
switches. The LTC3879 uses the on-resistance of the syn-
chronous power MOSFET to determine the inductor current.
The desired ripple current and operating frequency largely
determines the inductor value. Finally, CIN is selected for its
ability to handle the large RMS current into the converter,
and COUT is chosen with low enough ESR to meet output
voltage ripple and transient specications.
Maximum VDS Sense Voltage and VRNG Pin
Inductor current is measured by sensing the bottom
MOSFET VDS voltage that appears between the PGND
and SW pins. The maximum allowed VDS sense voltage is
set by the voltage applied to the VRNG pin and is approxi-
mately equal to (0.133)VRNG. The current mode control
loop does not allow the inductor current valleys to exceed
(0.133)VRNG. In practice, one should allow margin, to ac-
count for variations in the LTC3879 and external component
values. A good guide for setting VRNG is:
VRNG = 7.5 (Maximum VDS Sense Voltage)
An external resistive divider from INTVCC can be used
to set the voltage on the VRNG pin between 0.2V and 2V,
resulting in peak sense voltages between 26.6mV and
266mV. The wide peak voltage sense range allows for a
variety of applications and MOSFET choices. The VRNG pin
can also be tied to either SGND or INTVCC to force internal
defaults. When VRNG is tied to SGND, the device operates
at a valley current sense threshld of 30mV typical. If VRNG
is tied to INTVCC, the device operates at a valley current
sense threshold of 75mV typical.
Power MOSFET Selection
The LTC3879 requires two external N-channel power
MOSFETs, one for the top (main) switch and one for the
bottom (synchronous) switch. Important parameters for
the power MOSFETs are the breakdown voltage VBR(DSS),
threshold voltage VGS(TH), on-resistance RDS(ON), re-
verse transfer capacitance CRSS and maximum current
IDS(MAX).
The gate drive voltages are set by the 5.3V INTVCC supply.
Consequently, logic-level threshold MOSFETs must be used
in LTC3879 applications. If the input voltage is expected
to drop below 5V, then sub-logic level threshold MOSFETs
should be considered.
Using the bottom MOSFET as the current sense element
requires particular attention be paid to its on-resistance.
MOSFET on-resistance is typically specied with a maxi-
mum value RDS(ON)(MAX) at 25°C. In this case additional
margin is required to accommodate the rise in MOSFET
on-resistance with temperature.
R
Max V
Sense Voltage
I
DS ON MAX
DS
OT
()(
)
=
ρ
The
ρT term is a normalization factor (unity at 25°C)
accounting for the signicant variation in on-resistance
with temperature, typically about 0.4%/°C, as shown in
Figure 1. For a maximum junction temperature of 100°C
using a value of
ρT = 1.3 is reasonable.
The power dissipated by the top and bottom MOSFETs
depends upon their respective duty cycles and the load
current. When the LTC3879 is operating in continuous
mode, the duty cycles for the MOSFETs are:
D
V
D
VV
V
TOP
OUT
IN
BOT
IN
OUT
IN
=
–
Figure 1. RDS(ON) vs Temperature
JUNCTION TEMPERATURE (°C)
–50
TNORMALIZED
ON-RESIST
ANCE
(Ω)
1.0
1.5
150
3879 F01
0.5
0
50
100
2.0
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| LTC3880EUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤(pán) 包裝:Digi-Reel® 產(chǎn)品目錄頁(yè)面:1303 (CN2011-ZH PDF) 其它名稱(chēng):LM3754SQDKR |
| LTC3880EUJ#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤(pán) 包裝:帶卷 (TR) |
| LTC3880EUJ#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱(chēng):LM1771SSDX |
| LTC3880EUJ-1#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤(pán) 包裝:Digi-Reel® 產(chǎn)品目錄頁(yè)面:1303 (CN2011-ZH PDF) 其它名稱(chēng):LM3754SQDKR |
| LTC3880EUJ-1#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無(wú) 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤(pán) 包裝:帶卷 (TR) |
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