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參數(shù)資料
| 型號： | LTC4008EGN#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 4A, High Efficiency, Multi-Chemistry Battery Charger; Package: SSOP; No of Pins: 20; Temperature Range: -40°C to +125°C |
| 中文描述： | BATTERY CHARGE CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-20 |
| 文件頁數(shù)： | 8/24頁 |
| 文件大?。?/td> | 221K |
| 代理商： | LTC4008EGN#TRPBF |
LTC4008
16
4008fb
APPLICATIONS INFORMATION
Selection criteria for the power MOSFETs include the “ON”
resistance RDS(ON), total gate capacitance QG, reverse
transfer capacitance CRSS, input voltage and maximum
output current. The charger is operating in continuous
mode so the duty cycles for the top and bottom MOSFETs
are given by:
Main Switch Duty Cycle = VOUT/VIN
Synchronous Switch Duty Cycle = (VIN – VOUT)/VIN.
The MOSFET power dissipations at maximum output
current are given by:
PMAIN = VOUT/VIN(IMAX)2(1 + δΔT)RDS(ON)
+ k(VIN)2(IMAX)(CRSS)(fOSC)
PSYNC = (VIN – VOUT)/VIN(IMAX)2(1 + δΔT)RDS(ON)
Where
δΔT is the temperature dependency of RDS(ON) and
k is a constant inversely related to the gate drive current.
Both MOSFETs have I2R losses while the PMAIN equation
includes an additional term for transition losses, which
are highest at high input voltages. For VIN < 20V the high
current efciency generally improves with larger MOSFETs,
while for VIN > 20V the transition losses rapidly increase to
the point that the use of a higher RDS(ON) device with lower
CRSS actually provides higher efciency. The synchronous
MOSFET losses are greatest at high input voltage or during
a short circuit when the duty cycle in this switch in nearly
100%. The term (1 +
δΔT) is generally given for a MOSFET
in the form of a normalized RDS(ON) vs temperature curve,
but
δ = 0.005/°C can be used as an approximation for low
voltage MOSFETs. CRSS = QGD/ΔVDS is usually specied
in the MOSFET characteristics. The constant k = 2 can be
used to estimate the contributions of the two terms in the
main switch dissipation equation.
If the charger is to operate in low dropout mode or with
a high duty cycle greater than 85%, then the topside P-
channel efciency generally improves with a larger MOSFET.
Using asymmetrical MOSFETs may achieve cost savings
or efciency gains.
The Schottky diode D1, shown in the Typical Application
on the back page, conducts during the dead-time between
the conduction of the two power MOSFETs. This prevents
the body diode of the bottom MOSFET from turning on and
storing charge during the dead-time, which could cost as
much as 1% in efciency. A 1A Schottky is generally a good
size for 4A regulators due to the relatively small average
current. Larger diodes can result in additional transition
losses due to their larger junction capacitance.
The diode may be omitted if the efciency loss can be
tolerated.
Calculating IC Power Dissipation
The power dissipation of the LTC4008 is dependent upon
the gate charge of the top and bottom MOSFETs (QG1 &
QG2 respectively) The gate charge is determined from the
manufacturer’s data sheet and is dependent upon both
the gate voltage swing and the drain voltage swing of the
MOSFET. Use 6V for the gate voltage swing and VDCIN for
the drain voltage swing.
PD = VDCIN (fOSC (QG1 + QG2) + IQ)
Example:
VDCIN = 19V, fOSC = 345kHz, QG1 = QG2 = 15nC,
IQ = 5mA
PD = 292mW
Adapter Limiting
An important feature of the LTC4008 is the ability to auto-
matically adjust charging current to a level which avoids
overloading the wall adapter. This allows the product to
operate at the same time that batteries are being charged
without complex load management algorithms. Addition-
ally, batteries will automatically be charged at the maximum
possible rate of which the adapter is capable.
This feature is created by sensing total adapter output cur-
rent and adjusting charging current downward if a preset
adapter current limit is exceeded. True analog control is
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相關(guān)代理商/技術(shù)參數(shù) |
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| LTC4009 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:High Voltage High Current Controller for Battery Charging and Power Management |
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| LTC4009CUF#TRPBF | 功能描述:IC CHARGER BATTERY MC 20-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 電池管理 系列:- 標(biāo)準(zhǔn)包裝:61 系列:- 功能:電源管理 電池化學(xué):鋰離子（Li-Ion）、鋰聚合物（Li-Pol） 電源電壓:4.35 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:22-WFDFN 裸露焊盤 供應(yīng)商設(shè)備封裝:22-DFN（6x3）裸露焊盤 包裝:管件 |
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