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參數(shù)資料
| 型號： | LM3570 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | LED驅(qū)動器 |
| 英文描述： | Low Noise White LED Driver System |
| 中文描述： | 低噪聲白光LED驅(qū)動器系統(tǒng) |
| 文件頁數(shù)： | 10/13頁 |
| 文件大?。?/td> | 352K |
| 代理商： | LM3570 |
Application Information
PRE-REGULATION
The very low input current ripple of the LM3570, resulting
from internal pre-regulation, adds very little noise to the input
line. The core of the LM3570 is very similar to that of a basic
3/2 switched capacitor regulator: it is composed of seven
switches and two flying capacitors (external). Regulation is
achieved by modulating the on-resistance of the three
switches connected to the input pin (one switch in phase one
and two in phase two). The regulation is done before the
voltage “gain stage”, giving rise to the term "pre-regulation".
Pre-regulation eliminates most of the input current ripple that
is a typical and undesirable characteristic of many switched
capacitor converters.
TOTAL OUTPUT CURRENT CAPABILITY
The LM3570 is capable of providing a total output current of
80mA. The 80mA can be divided through any combination of
the three dedicated current outputs and/or current drawn
from the V
output. When pulling current from the V
pin, the LM3570 will hold the output voltage at the regulated
4.35V. This pre-regulation occurs when the input voltage is
within the 3.0V to 5.5V operating range. If the input voltage is
between the 2.7V to 3.0V range, the V
voltage will be-
have in the same manner as the output of an unregulated
charge pump. During operation in this input voltage range,
the output voltage becomes directly related to the total out-
put current drawn from the part and the output resistance
(R
) of the charge pump.
Figure 1
displays how the
LM3570’s R
OUT
is modeled to solve for the V
OUT
voltage
V
OUT
= (V
IN
x 1.5) - ( (I
+I
) x R
OUT
)
≤
V
IN
<
3.0V and R
OUT
= 4
Dx OUTPUT CURRENT CAPABILITY
An external resistor, R
, is connected to the I
pin to set
the current to be mirrored in each of the three LED outputs.
The internal current mirror sets each LED output current with
a 100:1 ratio to the current through R
. The current mirror
circuitry matches the current through each LED to within
0.5%. An equation for approximating the LED current is:
R
SET
=100 x (1.25V / I
DX
)
PARALLEL Dx OUTPUTS FOR INCREASED CURRENT
CAPABILITY
Outputs D
through D
may be connected together in any
combination to drive higher currents through fewer LEDs.
For example in
Figure 2
, outputs D
and D
are connected
together to drive one LED while D
1
is connected to a seper-
ate LED.
With this configuration, two parallel current sources of equal
value provide current to one of the LEDs. R
SET
should
therefore be chosen so that the current through each output
is programmed to 50% of the desired current through the
parallel connected LED. For example, if 40mA is the desired
drive current for the parallel connected LED, R
SET
should be
selected so that the current through each of the outputs is
20mA. Other combinations of parallel outputs may be imple-
mented in similar fashions, such as in
Figure 3
.
Connecting outputs in parallel does not affect internal opera-
tion of the LM3570 and has no impact on the Electrical
20085004
FIGURE 1. LM3570 Charge Pump Model
20085007
FIGURE 2. One Parallel Connected and One Singular
Connected LED
20085006
FIGURE 3. One Parallel Connected LED
L
www.national.com
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相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM3570SD | Low Noise White LED Driver System |
| LM3570SDX | Low Noise White LED Driver System |
| LM358 | Dual Operation Amplifiers |
| LM358CS | Voltage-Feedback Operational Amplifier |
| LM2904DBLE | Voltage-Feedback Operational Amplifier |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3570A E WAF | 制造商:Texas Instruments 功能描述: |
| LM3570SD | 制造商:Texas Instruments 功能描述:IC WLED DRIVER POWERWISE LLP-14 |
| LM3570SD/NOPB | 功能描述:IC LED DRIVR WHITE BCKLGT 14-LLP RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動器 系列:PowerWise® 標(biāo)準(zhǔn)包裝:1 系列:- 恒定電流:- 恒定電壓:- 拓?fù)?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(yīng)商設(shè)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 |
| LM3570SDX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Low Noise White LED Driver System |
| LM3578 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Switching Regulator |
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