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參數(shù)資料
| 型號： | LM3402MM |
| 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)： | 19/22頁 |
| 文件大小： | 840K |
| 代理商： | LM3402MM |
Design Example 2: LM3402HV
(Continued)
The next parameters to be determined are the forward cur-
rent rating and case size. In this example the high duty cycle
(D = 49.2 / 60 = 82%) places less thermals stress on D1 and
more on the internal power MOSFET of the LM3402. The
estimated average diode current is:
I
D
= 0.361 x 0.18 = 65 mA
A Schottky with a forward current rating of 0.5A would be
adequate, however at 100V the majority of diodes have a
minimum forward current rating of 1A. To determine the
proper case size, the dissipation and temperature rise in D1
can be calculated as shown in the Design Considerations
section. V
for a small case size such as SOD-123F in a
100V, 1A Schottky diode at 350 mA is approximately 0.65V
and the
θ
is 88C/W. Power dissipation and temperature
rise can be calculated as:
P
D
= 0.065 x 0.65 = 42 mW
T
RISE
= 0.042 x 88 = 4C
C
B
AND C
F
The bootstrap capacitor C
B
should always be a 10 nF ce-
ramic capacitor with X7R dielectric. A 25V rating is appropri-
ate for all application circuits. The linear regulator filter ca-
pacitor C
F
should always be a 100 nF ceramic capacitor,
also with X7R dielectric and a 25V rating.
EFFICIENCY
To estimate the electrical efficiency of this example the
power dissipation in each current carrying element can be
calculated and summed. Electrical efficiency,
η
, should not
be confused with the optical efficacy of the circuit, which
depends upon the LEDs themselves.
Total output power, P
O
, is calculated as:
P
O
= I
F
x V
O
= 0.361 x 49.2 = 17.76W
Conduction loss, P
C
, in the internal MOSFET:
P
C
= (I
F2
x R
DSON
) x D = (0.361
2
x 1.5) x 0.82 = 160 mW
Gate charging and VCC loss, P
G
, in the gate drive and linear
regulator:
P
= (I
+ f
SW
x Q
G
) x V
P
G
= (600 x 10
-6
+ 3 x 10
5
-9
) x 60 = 90 mW
Switching loss, P
S
, in the internal MOSFET:
P
= 0.5 x V
x I
x (t
R
+ t
) x f
5
P
S
= 0.5 x 60 x 0.361 x 40 x 10
-9
x 3 x 10
= 130 mW
AC rms current loss, P
CIN
, in the input capacitor:
P
CIN
= I
IN(rms)2
x ESR = (0.134)
2
x 0.006 = 0.1 mW (negli-
gible)
DCR loss, P
L
, in the inductor
P
L
= I
F2
x DCR = 0.35
2
x 1.1 = 135 mW
Recirculating diode loss, P
D
= 42 mW
Current Sense Resistor Loss, P
SNS
= 69 mW
Electrical efficiency,
η
= P
O
/ (P
O
+ Sum of all loss terms) =
17.76 / (17.76 + 0.62) = 96%
Temperature Rise in the LM3402HV IC is calculated as:
T
LM3402
= (P
C
+ P
G
+ P
) x
θ
= (0.16 + 0.084 + 0.13) x
200 = 74.8C
Layout Considerations
The performance of any switching converter depends as
much upon the layout of the PCB as the component selec-
tion. The following guidelines will help the user design a
circuit with maximum rejection of outside EMI and minimum
generation of unwanted EMI.
COMPACT LAYOUT
Parasitic inductance can be reduced by keeping the power
path components close together and keeping the area of the
loops that high currents travel small. Short, thick traces or
copper pours (shapes) are best. In particular, the switch
node (where L1, D1, and the SW pin connect) should be just
large enough to connect all three components without ex-
cessive heating from the current it carries. The LM3402/
02HV operates in two distinct cycles whose high current
paths are shown in Figure 6:
L
www.national.com
19
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|---|---|
| LM3402MM/HALF | 制造商:Texas Instruments 功能描述:DRIVER LED 0.5A POWERWISE MSOP8 |
| LM3402MM/NOPB | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 0.5A CONSTANT CRNT BUCK REG 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(guān)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 |
| LM3402MMX | 功能描述:開關(guān)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(guān)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 |
| LM3402MMX/NOPB | 功能描述:開關(guān)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(guān)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 |
| LM3402MR | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 6V to 42V 8-Pin PSOP EP Rail |
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