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參數(shù)資料
| 型號： | LM3402HVMM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.5A Constant Current Buck Regulator for Driving High Power LEDs |
| 中文描述： | 0.94 A SWITCHING REGULATOR, PDSO8 |
| 封裝： | PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 15/22頁 |
| 文件大?。?/td> | 840K |
| 代理商： | LM3402HVMM |
Design Example 1: LM3402
(Continued)
R
ON
and t
ON
To select R
ON
the expression relating t
ON
to input voltage
from the Controlled On-time Overview section can be re-
written as:
Minimum on-time occurs at the maximum V
IN
, which is 24V
x 110% = 26.4V. R
ON
is therefore calculated as:
R
ON
= (300 x 10
-9
x 26.4) / 1.34 x 10
-10
= 59105
The closest 1% tolerance resistor is 59.0 k
. The switching
frequency of the circuit can then be found using the equation
relating R
ON
to f
SW
:
f
SW
= 3.7 / (59000 x 1.34 x 10
-10
) = 468 kHz
USING AN OUTPUT CAPACITOR
The inductor will be the largest component used in this
design. Because the application does not require any PWM
dimming, an output capacitor can be used to greatly reduce
the inductance needed without worry of slowing the potential
PWM dimming frequency. The total solution size will be
reduced by using an output capacitor and small inductor as
opposed to one large inductor.
OUTPUT INDUCTOR
Knowing that an output capacitor will be used, the inductor
can be selected for a larger current ripple. The desired
maximum value for
i
L
is
±
30%, or 0.6 x 350 mA = 210
mA
P-P
. Minimum inductance is selected at the maximum
input voltage. Re-arranging the equation for current ripple
selection yields the following:
L
MIN
= [(26.4 – 3.7) x 300 x 10
-9
] / (0.6 x 0.35) = 32.4 μH
The closest standard inductor value is 33 μH. Off-the-shelf
inductors rated at 33 μH are available from many magnetics
manufacturers.
Inductor datasheets should contain three specifications
which are used to select the inductor. The first of these is the
average current rating, which for a buck regulator is equal to
the average load current, or I
. The average current rating is
given by a specified temperature rise in the inductor, nor-
mally 40C. For this example, the average current rating
should be greater than 350 mA to ensure that heat from the
inductor does not reduce the lifetime of the LED or cause the
LM3402 to enter thermal shutdown.
The second specification is the tolerance of the inductance
itself, typically
±
10% to
±
30% of the rated inductance. In this
example an inductor with a tolerance of
±
20% will be used.
With this tolerance the typical, minimum, and maximum in-
ductor current ripples can be calculated:
i
L(TYP)
= [(26.4 – 3.7) x 300 x 10
-9
] / 33 x 10
-6
= 206 mA
P-P
i
L(MIN)
= [(26.4 – 3.7) x 300 x 10
-9
] / 39.6 x 10
-6
= 172 mA
P-P
i
L(MAX)
= [(26.4 – 3.7) x 300 x 10
-9
] / 26.4 x 10
-6
= 258 mA
P-P
The third specification for an inductor is the peak current
rating, normally given as the point at which the inductance
drops off by a given percentage due to saturation of the core.
The worst-case peak current occurs at maximum input volt-
age and at minimum inductance, and can be determined
with the equation from the Design Considerations section:
20192119
FIGURE 5. Schematic for Design Example 1
L
www.national.com
15
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM3402HVMM/NOPB | 功能描述:開關變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM3402HVMMX | 功能描述:開關變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM3402HVMMX/NOPB | 功能描述:開關變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM3402HVMR | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 6V to 75V 8-Pin PSOP EP Rail 制造商:Texas Instruments 功能描述:Buck Reg for Hi Pwr LED Drvs, LM3402HVMR |
| LM3402HVMR/NOPB | 功能描述:開關變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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