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參數(shù)資料
| 型號： | LM2795 |
| 文件頁數(shù)： | 10/14頁 |
| 文件大?。?/td> | 373K |
| 代理商： | LM2795 |
Circuit Description
The LM2794/5 employs a fractional charge-pump technique
to step up the output voltage to 1.5 times the input voltage.
The charge-pump provides the voltage that is needed by the
four matched internal current sources to drive high forward
voltage drop LEDs from Li-Ion battery sources. The part has
on-chip current regulators which are composed of current
mirrors with a 10 to 1 ratio. The mirrors control the LED
current without using current limiting resistors in the LED
current path. The device can drive up to a total of 80mA
through the LEDs.
Functional Block Diagram
The LED brightness can be controlled by both analog and/or
digital methods. The digital technique uses a PWM (Pulse
Width Modulation) signal applied to the shutdown input. The
analog technique applies an analog voltage to the brightness
(BRGT) pin. Please refer to table 4 in the application infor-
mation section for a quick reference table on BRGT voltage
and R
SET
selections. Futhermore, the LM2794/5 can be
used for constant brightness by grounding the BRGT pin .
20028530
Application Information
SOFT START
LM2794 includes a soft start function to reduce the inrush
currents and high peak current during power up of the de-
vice. This is done to reduce stress on the LM2794/5 and
external components. During soft start, the switch resis-
tances limit the inrush current used to charge the flying and
hold capacitors.
SHUTDOWN MODE
A shutdown pin (SD or SD) is available to disable the
LM2794/5 and reduce the quiescent current to 5μA maxi-
mum.
During normal operation mode of the LM2794, applying an
active high logic signal to the SD pin or tying the SD pin to
V
IN
will enable the device. Pulling SD low or connecting SD
to ground will disable the device.
During normal operation mode of the LM2795, applying an
active low logic signal to the SD pin or tying the SD pin to
GND will enable the device. Pulling SD high or connecting
SD to V
IN
will disable the device.
CAPACITOR SELECTION
Low equivalent series resistance (ESR) capacitors such as
X5R or X7R are recommended to be used for C
, C1, C2,
and C
for best performance. Ceramic capacitors with
less than or equal to 0.3 ohms ESR value are recommended
for this application.
Table 1
below lists suggested capacitor
suppliers for the typical application circuit.
TABLE 1. Low ESR Capacitor Manufactures
Manufacturer
TDK
Contact
(847) 803
6100
(800) 831
9172
(800) 348
2496
website
www.component.tdk.com
MuRata
www.murata.com
Taiyo Yuden
www.t-yuden.com
L
www.national.com
10
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM27951 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:White LED Adaptive 1.5X/1X Switched Capacitor Current Driver |
| LM27951SD | 功能描述:LED照明驅動器 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: 安裝風格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM27951SD/NOPB | 功能描述:LED照明驅動器 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: 安裝風格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM27951SDX | 功能描述:LED照明驅動器 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: 安裝風格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM27951SDX/NOPB | 功能描述:LED照明驅動器 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: 安裝風格:SMD/SMT 封裝 / 箱體:SO-16N |
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