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參數(shù)資料
| 型號： | LM3520 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | LED驅(qū)動器 |
| 英文描述： | Integrated White LED Driver with Organic LED Display Power Supply |
| 中文描述： | 集成白光LED有機LED顯示屏驅(qū)動電源 |
| 文件頁數(shù)： | 11/14頁 |
| 文件大?。?/td> | 963K |
| 代理商： | LM3520 |
Circuit Description
The LM3520 is designed for White LED & OLED backlighting
in mobile phone applications. It has a main display loop
which can drive up to 5 white LEDS in series and a sub
display loop which is designed to drive OLED up to 20V/50
mA. The main display loop employs a fixed frequency cur-
rent mode scheme to regulate the LED current. The sub
display loop employs a fixed frequency gated oscillator
scheme to regulate the output voltage. The device has two
independent control pins to enable the Main or Sub displays.
Note that both displays can not be ON at the same time.
PWM Operation
The LM3520 utilizes a synchronous Current Mode PWM
control scheme to regulate the feedback voltage over all load
and line conditions for the main display. The LM3520 is
internally compensated preventing the need for external
compensation components yielding a compact solution. The
operation can best be understood referring to the functional
block diagram. The LM3520 operates as follows: During the
first cycle, the oscillator sets the driver logic and turns on the
NMOS power device conducting current through the inductor
and reverse biases the external diode isolating the output
from the V
SW
node.
The LED current is supplied by the output capacitor when
the NMOS power device is active. During this cycle, the
output voltage of the EAMP controls the current through the
inductor. This voltage will increase for larger loads and de-
crease for smaller loads limiting the peak current in the
inductor. The sum of the EAMP voltage and voltage ramp is
compared with the sensed switch voltage. Once these volt-
ages are equal, the PWM COMP will then reset the logic
turning off the NMOS power device and forward biasing the
external diode to the white LED load and flows through the
diode to the white LED load and output capacitor. The induc-
tor current recharges the output capacitor and supplies the
current for the white LED branches. The oscillator then sets
the driver logic again repeating the process.
PFM Operation
The LM3520 utilizes a gated oscillator control scheme for the
sub-display. There is a hysteresis window to regulate the
output voltage. The oscillator frequency is the same as the
frequency in PWM control. The Duty cycle of the oscillator
signal is always set to maximum. During the first part of each
switching cycle, the internal NMOS switch is turned on until
the PFM current limit is reached. When the NMOS is off, the
voltage of the inductor reverses and forces current through
the diode to the output capacitor. This process continues
until the upper comparator hysteresis is reached at which
point the NMOS is disabled until the lower comparator
threshold is reached and the process repeats again.
Current Limit Protection
The LM3520 has current limiting protection to prevent exces-
sive stress on itself and external components during over-
load conditions. The internal current limit comparator will
disable the NMOS power device at a typical switch peak
current limit of 700 mA.
Output Over-Voltage Protection
The LM3520 contains dedicated circuitry for monitoring the
output voltage. In the event that the primary LED network is
disconnected the output will increase and be limited to 23.2V
(typ.). There is a~1V hysteresis associated with this cir-
cuitry, which will turn the NMOS off when the output voltage
is at 24.2V(max.) until the output voltage reach 22.5V(typ.)
or lower. The 23.5V limit allows the use of 25V 1 μF ceramic
output capacitors creating an overall small solution for white
LED applications.
Under Voltage Protection
The LM3520 has an UVP comparator to turn the NMOS
power device off in case the input voltage or battery voltage
is too low preventing an on state of the power device con-
ducting large amounts of current.
Reliability and Thermal Shutdown
The LM3520 has an internal thermal shutdown function to
protect the die from excessive temperatures. The thermal
shutdown trip point is typically 160C, Normal operation re-
sumes when the temperature drops below 140C.
Startup
The LM3520 does not include a power on reset circuit and
relies on external signal to monitor enable signal. In the
event of under voltage condition, the device enable pin must
be brought low until the input voltage is above the minimum
guarantee voltage (2.7V).
Application Information
SETTING LED CURRENT
The White LED current is set using the following equation:
For main display:
(1)
PWM CONTROL
The LED current can be controlled using a PWM signal on
the enable pin with frequencies in the range of 100 Hz to
1 kHz. LM3520 LED current can be controlled with PWM
signal frequencies above 1 kHz but LED current is not
linearly porportional to the duty cycle. The maximum LED
current would be achieved using the equation above with
100% duty cycle, ie. The enable pin is always high.
SETTING SUB VOLTAGE
Sub-display voltage is be set by choosing R
and R
SUB2
as illustrated in
Figure 4
. V
SUB
is calculated as follow:
(2)
L
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11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3520_0509 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Integrated White LED Driver with Organic LED Display Power Supply |
| LM3520B WAF | 制造商:Texas Instruments 功能描述: |
| LM3520SD | 制造商:Texas Instruments 功能描述:WLED/OLED DRIVER POWERWISE LLP-14 |
| LM3520SD | 制造商:Texas Instruments 功能描述:IC WLED/DISPLAY DRIVER POWERWISE |
| LM3520SD/NOPB | 功能描述:IC LED DRVR WT/OLED BCKLGT 14LLP RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動器 系列:- 標準包裝:1 系列:- 恒定電流:- 恒定電壓:- 拓撲:PWM，切換式電容器（充電泵） 輸出數(shù):1 內(nèi)部驅(qū)動器:是 類型 - 主要:背光 類型 - 次要:白色 LED 頻率:642kHz 電源電壓:2.7 V ~ 5.5 V 輸出電壓:5V 安裝類型:表面貼裝 封裝/外殼:10-VFDFN 裸露焊盤 供應商設備封裝:10-VSON 包裝:剪切帶 (CT) 工作溫度:-30°C ~ 85°C 產(chǎn)品目錄頁面:1371 (CN2011-ZH PDF) 其它名稱:BD1603NUV-E2CT |
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