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參數(shù)資料
| 型號： | LM3502 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Step-Up Converter for White LED Applications |
| 中文描述： | 升壓轉(zhuǎn)換器的白色發(fā)光二極管應(yīng)用 |
| 文件頁數(shù)： | 16/18頁 |
| 文件大?。?/td> | 928K |
| 代理商： | LM3502 |
Application Information
(Continued)
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Yuden
muRata
GMK212BJ105MD
(0805/35V)
GRM40-035X7R105K
(0805/50V)
C3216X7R1H105KT
(1206/50V)
C3216X7R1C475K
(1206/16V)
08053D105MAT
(0805/25V)
08056D475KAT
(0805/6.3V)
1206ZD475MAT
(1206/10V)
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www.murata.com
TDK
www.tdktca.com
AVX
www.avxcorp.com
DIODE SELECTION
To maintain high efficiency it is recommended that the aver-
age current rating (I
or I
) of the selected diode should be
larger than the peak inductor current (I
). At the mini-
mum, the average current rating of the diode should be
larger than the maximum LED current. To maintain diode
integrity the peak repetitive forward current (I
) must be
greater than or equal to the peak inductor current (I
).
Diodes with low forward voltage ratings (V
) and low junction
capacitance magnitudes (C
or C
or C
) are conducive to
high efficiency. The chosen diode must have a reverse
breakdown voltage rating (V
and/or V
) that is larger
than the output voltage (V
). No matter what type of diode
is chosen, Schottky or not, certain selection criteria must be
followed:
1.
V
R
and V
RRM
>
V
OUT
2.
I
F
or I
O
≥
I
LOAD
or I
OUT
3.
I
FRM
≥
I
Lpeak
Some recommended diode manufacturers included but are
not limited to:
Vishay
SS12(1A/20V)
SS14(1A/40V)
SS16(1A/60V)
MBRM120E
(1A/20V)
MBRS1540T3
(1.5A/40V)
MBR240LT
(2A/40V)
CMSH1- 40M
(1A/40V)
www.vishay.com
On
Semiconductor
www.onsemi.com
Central
Semiconductor
www.centralsemi.com
SHUTDOWN AND START-UP
On startup, the LM3502 contains special circuitry that limits
the peak inductor current which prevents large current
spikes from loading the battery or power supply. When Cntrl
≥
1.4V and both the En1 and En2 signals are less than 0.3V,
the LM3502 will enter a low I
state and regulation will end.
During this low I
mode the output voltage is a diode drop
below the supply voltage and the soft-start will be reset to
limit the peak inductor current at the next startup. When both
En1 and En2 are less than 0.3V, the P1 PMOS and N2
NMOS switches will turn off.
When Cntrl
<
0.3V for more than 12ms, typicaly, the LM3502
will shutdown and the output voltage will be a diode drop
below the supply voltage. If the Cntrl pin is low for more than
12ms, the soft-start will reset to limit the peak inductor cur-
rent at the next startup.
When Cntrl is
<
0.3 but for less than 12ms, typically, the
device will not shutdown and reset the soft-start but shut off
the NMOS N1 Power Device to allow for PWM contrl of the
LED current.
THERMAL SHUTDOWN
The LM3502 stops regulating when the internal semiconduc-
tor junction temperature reaches approximately 140C. The
internal thermal shutdown has approximately 20C of hyster-
esis which results in the LM3502 turning back on when the
internal semiconductor junction temperature reaches 120C.
When the thermal shutdown temperature is reached, the
softstart is reset to prevent inrush current when the die
temperature cools.
UNDER VOLTAGE PROTECTION
The LM3503 contains protection circuitry to prevent opera-
tion for low input supply voltages. When Vin drops below
2.3V, typically the LM3502 will no longer regulate. In this
mode, the output volage will be one diode drop below Vin
and the softstart will be reset. When Vin increases above
2.4V, typically, the device will begin regulating again.
OVER VOLTAGE PROTECTION
The LM3502 contains dedicated circuitry for monitoring the
output voltage. In the event that the LED network is discon-
nected from the LM3502, the output voltage will increase
and be limited to 15.5V(typ.) for the 16V version , 24V(typ.)
for the 25V version, 34V(typ.) for the 35V version and
42V(typ.) for the 44V version (see eletrical table for more
details). In the event that the network is reconnected, regu-
lation will resume at the appropriate output voltage.
LAYOUT CONSIDERATIONS
All components, except for the white LEDs, must be placed
as close as possible to the LM3502. The die attach pad
(DAP) must be soldered to the ground plane.
The input bypass capacitor C
, as shown in
Figure 1
, must
be placed close to the IC and connect between the V
and
PGND pins. This will reduce copper trace resistance which
effects input voltage ripple of the IC. For additional input
voltage filtering, a 100nF bypass capacitor can be placed in
parallel with C
to shunt any high frequency noise to
ground. The output capacitor, C
, must be placed close to
the IC and be connected between the V
and PGND
pins. Any copper trace connections for the C
capacitor
can increase the series resistance, which directly effects
output voltage ripple and efficiency. The current setting re-
sistor, R1, should be kept close to the Fb pin to minimize
copper trace connections that can inject noise into the sys-
tem. The ground connection for the current setting resistor
network should connect directly to the PGND pin. TheAGND
pin should be tied directly to the PGND pin. Trace connec-
tions made to the inductor should be minimized to reduce
power dissipation and increase overall efficiency while re-
ducing EMI radiation. For more details regarding layout
guidelines for switching regulators, refer toApplications Note
AN-1149.
L
www.national.com
16
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3502_06 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Step-Up Converter for White LED Applications |
| LM3502ITL/NOPB | 制造商:Texas Instruments 功能描述: |
| LM3502ITL-16 | 制造商:Texas Instruments 功能描述:WLED DRIVER 16V POWERWISE LLP-16 |
| LM3502ITL-16/NOPB | 功能描述:LED照明驅(qū)動器 RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM3502ITL-25 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述:WLED DRIVER 25V POWERWISE LLP-16 |
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