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參數(shù)資料
| 型號(hào)： | LM2794TL |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Current Regulated Switched Capacitor LED Supply with Analog and PWM Brightness Control |
| 中文描述： | SWITCHED CAPACITOR REGULATOR, 675 kHz SWITCHING FREQ-MAX, PBGA14 |
| 封裝： | CSP-14 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大?。?/td> | 487K |
| 代理商： | LM2794TL |
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Application Information
(Continued)
SHUTDOWN MODE
The shutdown pin (SD) disables the part and reduces the
quiescent current to 2.3μA (typ.).
The LM2795 has an active-high shutdown pin (HIGH =
shutdown, LOW = operating). An internal pull-up is con-
nected between SD and V
of the LM2795. This allows the
use of open-drain logic control of the LM2795 shutdown, as
shown in
Figure 1
. The LM2795 SD pin can also be driven
with a rail-to-rail CMOS logic signal.
The LM2794 has an active-low shutdown pin (LOW = shut-
down, HIGH = operating). The LM2794 SD pin can be driven
with a low-voltage CMOS logic signal (1.5V logic, 1.8V logic,
etc). There is no internal pull-up or pull-down on the SD pin
of the LM2794.
CAPACITOR SELECTION
The LM2794/5 requires 4 external capacitors for proper
operation. Surface-mount multi-layer ceramic capacitors are
recommended. These capacitors are small, inexpensive and
have very low equivalent series resistance (ESR,
≤
15m
typ.). Tantalum capacitors, OS-CON capacitors, and alumi-
num electrolytic capacitors are generally not recommended
for use with the LM2794/5 due to their high ESR, as com-
pared to ceramic capacitors.
For most applications, ceramic capacitors with X7R or X5R
temperature characteristic are preferred for use with the
LM2794/5. These capacitors have tight capacitance toler-
ance (as good as
±
10%), hold their value over temperature
(X7R:
±
15% over 55C to 125C; X5R:
±
15% over 55C
to 85C), and typically have little voltage coefficient. Capaci-
tors with Y5V or Z5U temperature characteristic are gener-
ally not recommended for use with the LM2794/5. Capaci-
tors with these temperature characteristics typically have
wide capacitance tolerance (+80%, 20%), vary significantly
over temperature (Y5V: +22%, 82% over 30C to +85C
range; Z5U: +22%, 56% over +10C to +85C range), and
have poor voltage coefficients. Under some conditions, a
nominal 1μF Y5V or Z5U capacitor could have a capacitance
of only 0.1μF. Such detrimental deviation is likely to cause
Y5V and Z5U capacitors to fail to meet the minimum capaci-
tance requirements of the LM2794/5.
Table 1
lists suggested
capacitor suppliers for the typical application circuit.
TABLE 1. Ceramic Capacitor Manufacturers
Manufacturer
TDK
Murata
Taiyo Yuden
Contact
www.component.tdk.com
www.murata.com
www.t-yuden.com
LED SELECTION
The LM2794/5 is designed to drive LEDs with a forward
voltage of about 3.0V to 4.0V. The typical and maximum
diode forward voltage depends highly on the manufacturer
and their technology.
Table 2
lists two suggested manufac-
turers. Forward current matching is assured over the LED
process variations due to the constant current output of the
LM2794/5.
TABLE 2. White LED Selection
Manufacturer
Osram
Nichia
Contact
www.osram-os.com
www.nichia.com
I
SET
AND BRGT PINS
An external resistor, R
, is connected to the I
pin to set
the current to be mirrored in each of the LED outputs. The
internal current mirror sets each LED output current with a
10:1 ratio to the current through R
SET
. The current mirror
circuitry matches the current through each LED to within
0.5%.
In addition to R
SET
, a voltage may be applied to the V
BRGT
pin to vary the LED current. By adjusting current with the
Brightness pin (BRGT), the brightness of the LEDs can be
smoothly varied.
Applying a voltage on BRGT between 0 to 3 volts will linearly
vary the LED current. Voltages above 3V do not increase the
LED current any further. The voltage on the V
pin is fed
into an internal resistor network with a ratio of 0.385. The
resulting voltage is then summed with a measured offset
voltage of 0.188V, which comes from the reference voltage
being fed through a resistor network (See
Functional Block
Diagram
). The brightness control circuitry then uses the
summed voltage to control the voltage across R
SET
. An
equation for approximating the LED current is:
20028540
20028536
FIGURE 1. Open-Drain Logic Shutdown Control
L
www.national.com
10
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2794TL/NOPB | 功能描述:LED照明驅(qū)動(dòng)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 |
| LM2794TLX | 功能描述:IC LED DRVR WHT BCKLT 14USMD RoHS:否 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動(dòng)器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 恒定電流:- 恒定電壓:- 拓?fù)?升壓（升壓），切換式電容器（充電泵） 輸出數(shù):1 內(nèi)部驅(qū)動(dòng)器:是 類型 - 主要:背光 類型 - 次要:白色 LED 頻率:625kHz ~ 875kHz 電源電壓:2.7 V ~ 5.3 V 輸出電壓:5V 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應(yīng)商設(shè)備封裝:10-µMAX 包裝:帶卷 (TR) 工作溫度:-40°C ~ 85°C |
| LM2794TLX/NOPB | 功能描述:LED照明驅(qū)動(dòng)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 |
| LM2795 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| 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 |
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