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參數(shù)資料
| 型號(hào)： | LTC3544EUD |
| 廠(chǎng)商： | LINEAR TECHNOLOGY CORP |
| 元件分類(lèi)： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 2700 kHz SWITCHING FREQ-MAX, PQCC16 |
| 封裝： | 3 X 3 MM, LEAD FREE, PLASTIC, MO220WEED-2, QFN-16 |
| 文件頁(yè)數(shù)： | 4/16頁(yè) |
| 文件大小： | 295K |
| 代理商： | LTC3544EUD |
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LTC3544
12
3544fa
top and bottom MOSFET RDS(ON) and the duty cycle
(DC) as follows:
RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC)
The RDS(ON) for both the top and bottom MOSFETs can
be obtained from the Typical Performance Characteristics
curves. Thus, to obtain I2R losses, simply add RSW to
RL and multiply the result by the square of the average
output current.
Other losses when in switching operation, including CIN
and COUT ESR dissipative losses and inductor core losses,
generally account for less than 2% total additional loss.
Thermal Considerations
The LTC3544 requires the package backplane metal to be
well soldered to the PC board. This gives the QFN package
exceptional thermal properties, making it difcult in normal
operation to exceed the maximum junction temperature
of the part. In most applications the LTC3544 does not
dissipate much heat due to its high efciency. In appli-
cations where the LTC3544 is running at high ambient
temperature with low supply voltage and high duty cycles,
such as in dropout, the heat dissipated may exceed the
maximum junction temperature of the part if it is not well
thermally grounded. If the junction temperature reaches
approximately 150°C, the power switches will be turned
off and the SW nodes will become high impedance.
To avoid the LTC3544 from exceeding the maximum junc-
tion temperature, the user will need to do some thermal
analysis. The goal of the thermal analysis is to determine
whether the power dissipated exceeds the maximum
junction temperature of the part. The temperature rise is
given by:
TR = PD θJA
where PD is the power dissipated by the regulator and θJA
is the thermal resistance from the junction of the die to
the ambient temperature.
The junction temperature, TJ, is given by:
TJ = TA + TR
where TA is the ambient temperature.
As an example, consider the LTC3544 in dropout at an
input voltage of 2.5V, a total load current (all four regula-
tors) of 800mA and an ambient temperature of 85°C. From
the Typical Performance graphs of switch resistance, the
RDS(ON) of the 300mA P-channel switch at 85°C can be
estimated as 0.67Ω. Therefore, power dissipated by the
300mA channel is:
PD = ILOAD2 RDS(ON) = 60mW
Similar analysis on the other channels gives a total power
dissipation of 138mW. For the 3mm × 3mm QFN package,
the θJA is 68°C/W. Thus, the junction temperature of the
regulator is:
TJ = 85°C + (0.138)(68) = 94.4°C
which is well below the maximum junction temperature
of 125°C.
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance RDS(ON).
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to (ΔILOAD ESR), where ESR is the effective series
resistance of COUT. ΔILOAD also begins to charge or dis-
charge COUT, which generates a feedback error signal. The
regulator loop then acts to return VOUT to its steady-state
value. During this recovery time VOUT can be monitored
for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
A second, more severe transient is caused by switching
in loads with large (>1μF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in paral-
lel with COUT, causing a rapid drop in VOUT. No regulator
can deliver enough current to prevent this problem if the
load switch resistance is low and it is driven quickly. The
only solution is to limit the rise time of the switch drive
so that the load rise time is limited to approximately (25
CLOAD). Thus, a 10μF capacitor charging to 3.3V would
require a 250μs rise time, limiting the charging current
to about 130mA.
APPLICATIONS INFORMATION
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LTC3544EUD#PBF | 功能描述:IC REG BUCK SYNC ADJ QUAD 16QFN 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 |
| LTC3544EUD#TRPBF | 功能描述:IC REG BUCK SYNC ADJ QUAD 16QFN 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:2,500 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，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(lèi)型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤(pán) 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤(pán) |
| LTC3544EUDPBF | 制造商:Linear Technology 功能描述:2.25MHz Sync Step-Down Converter LTC3544 |
| LTC3544EUD-PBF | 制造商:LINER 制造商全稱(chēng):Linear Technology 功能描述:Quad Synchronous Step-Down Regulator: 2.25MHz, 300mA, 200mA, 200mA, 100mA |
| LTC3544EUD-TR | 制造商:LINER 制造商全稱(chēng):Linear Technology 功能描述:Quad Synchronous Step-Down Regulator: 2.25MHz, 300mA, 200mA, 200mA, 100mA |
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