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参数资料
| 型号： | LM2794BL/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHED CAPACITOR REGULATOR, 675 kHz SWITCHING FREQ-MAX, PBGA14 |
| 封装： | LEAD FREE, CSP-14 |
| 文件页数： | 2/16页 |
| 文件大小： | 487K |
| 代理商： | LM2794BL/NOPB |
Application Information (Continued)
SHUTDOWN MODE
The shutdown pin (SD) disables the part and reduces the
quiescent current to 2.3A (typ.).
The LM2795 has an active-high shutdown pin (HIGH =
shutdown, LOW = operating). An internal pull-up is con-
nected between SD and V
IN 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 1F Y5V or Z5U capacitor could have a capacitance
of only 0.1F. 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
Contact
TDK
www.component.tdk.com
Murata
www.murata.com
Taiyo Yuden
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
Contact
Osram
www.osram-os.com
Nichia
www.nichia.com
I
SET AND BRGT PINS
An external resistor, R
SET, is connected to the ISET 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 VBRGT
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
BRGT 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
LM2794/LM2795
www.national.com
10
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| LM2794BLX | 制造商:Texas Instruments 功能描述: |
| LM2794EVAL | 功能描述:电源管理IC开发工具 EVAL KIT FOR LM2794 RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM2794TL | 功能描述:IC LED DRVR WHT BCKLT 14MICROSMD RoHS:否 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 恒定电流:- 恒定电压:- 拓扑:升压（升压），切换式电容器（充电泵） 输出数:1 内部驱动器:是 类型 - 主要:背光 类型 - 次要:白色 LED 频率:625kHz ~ 875kHz 电源电压:2.7 V ~ 5.3 V 输出电压:5V 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-µMAX 包装:带卷 (TR) 工作温度:-40°C ~ 85°C |
| LM2794TL/NOPB | 功能描述:LED照明驱动器 RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
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