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參數(shù)資料
| 型號： | LM3500TLX-21 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 顯示驅(qū)動器 |
| 英文描述： | Synchronous Step-up DC/DC Converter for White LED |
| 中文描述： | LED DISPLAY DRIVER, BGA8 |
| 封裝： | MICRO, SMD-8 |
| 文件頁數(shù)： | 13/18頁 |
| 文件大?。?/td> | 1072K |
| 代理商： | LM3500TLX-21 |
Application Information
ADJUSTING LED CURRENT
The White LED current is set using the following equation:
The LED current can be controlled using a PWM signal on
the SHDN pin with frequencies in the range of 100Hz
(greater than visible frequency spectrum) to 1kHz. For con-
trolling LED currents down to the μA levels, it is best to use
a PWM signal frequency between 200-500Hz. The LM3500
LED current can be controlled with PWM signal frequencies
above 1kHz but the controllable current decreases with
higher frequency. The maximum LED current would be
achieved using the equation above with 100% duty cycle, ie.
the SHDN pin always high.
LED-DRIVE CAPABILITY
The maximum number of LEDs that can be driven by the
LM3500 is limited by the output voltage capability of the
LM3500. When using the LM3500 in the typical application
configuration, with LEDs stacked in series between the V
OUT
and FB pins, the maximum number of LEDs that can be
placed in series (N
MAX
) is dependent on the maximum LED
forward voltage (V
F-MAX
), the voltage of the LM3500 feed-
back pin (V
FB-MAX
= 0.53V), and the minimum output over-
voltage protection level of the chosen LM3500 option
(LM3500-16: OVP
MIN
= 15V; LM3500-21: OVP
MIN
= 20V).
For the circuit to function properly, the following inequality
must be met:
(N
MAX
x V
F-MAX
) + 0.53V
≤
OVP
MIN
When inserting a value for maximim LED V
, LED forward
voltage variation over the operating temperature range
should be considered. The table below provides maximum
LED voltage numbers for the LM3500-16 and LM3500-21 in
the typical application circuit configuration (with 3, 4, 5, 6, or
7 LEDs placed in series between the V
OUT
and FB pins).
# of LEDs
(in series)
3
4
5
6
7
Maximum LED V
F
LM3500-16
4.82V
3.61V
2.89V
X
X
LM3500-21
6.49V
4.86V
3.89V
3.24V
2.78V
For the LM3500 to operate properly, the output voltage must
be kept above the input voltage during operation. For most
applications, this requires a minimum of 2 LEDs (total of 6V
or more) between the FB and V
OUT
pins.
OUTPUT OVERVOLTAGE PROTECTION
The LM3500 contains dedicated circuitry for monitoring the
output voltage. In the event that the primary LED network is
disconnected from the LM3500-16, the output voltage will
increase and be limited to 15.5V (typ.). There is a 900mV
hysteresis associated with this circuitry which will cause the
output to fluctuate between 15.5V and 14.6V (typ.) if the
primary network is disconnected. In the event that the net-
work is reconnected regulation will begin at the appropriate
output voltage. The 15.5V limit allows the use of 16V 1μF
ceramic output capacitors creating an overall small solution
for white LED applications.
In the event that the primary LED network is disconnected
from the LM3500-21, the output voltage will increase and be
limited to 20.5V (typ.). There is a 1V hysteresis associated
with this circuitry which will cause the output to fluctuate
between 20.5V and 19.5V (typ.) if the primary network is
disconnected. In the event that the network is reconnected
regulation will begin at the appropriate output voltage. The
20.5V limit allows the use of 25V 1μF ceramic output capaci-
tors.
RELIABILITY AND THERMAL SHUTDOWN
The maximum continuous pin current for the 8 pin thin micro
SMD package is 535mA. When driving the device near its
power output limits the V
SW
pin can see a higher DC current
than 535mA (see
INDUCTOR SELECTION
section for aver-
age switch current). To preserve the long term reliability of
the device the average switch current should not exceed
535mA.
The LM3500 has an internal thermal shutdown function to
protect the die from excessive temperatures. The thermal
shutdown trip point is typically 150C. There is a hysteresis
of typically 35C so the die temperature must decrease to
approximately 115C before the LM3500 will return to normal
operation.
INDUCTOR SELECTION
The inductor used with the LM3500 must have a saturation
current greater than the cycle by cycle peak inductor current
(see
Typical Peak Inductor Currents
table below). Choosing
inductors with low DCR decreases power losses and in-
creases efficiency.
The minimum inductor value required for the LM3500-16 can
be calculated using the following equation:
The minimum inductor value required for the LM3500-21 can
be calculated using the following equation:
For both equations above, L is in μH, V
is the input supply
of the chip in Volts, R
is the ON resistance of the NMOS
power switch found in the
Typical Performance Characteris-
tics
section in ohms and D is the duty cycle of the switching
regulator. The above equation is only valid for D greater than
or equal to 0.5. For applications where the minimum duty
cycle is less than 0.5, a 22μH inductor is the typical recom-
mendation for use with most applications. Bench-level veri-
fication of circuit performance is required in these special
cases, however. The duty cycle, D, is given by the following
equation:
where V
OUT
is the voltage at pin C1.
L
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3500TLX-21/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 |
| LM3501 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Synchronous Step-up DC/DC Converter for White LED Applications |
| LM3501TL-16 | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Up 2.7V to 7V 8-Pin uSMD T/R 制造商:Texas Instruments 功能描述:IC, WHITE LED DRIVER, POWERWISE 制造商:Texas Instruments 功能描述:Display Driver,4LED,LM3501TL-16 |
| LM3501TL-16/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3501TL-16EV | 功能描述:電源管理IC開發(fā)工具 LM3501TL-16 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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