參數(shù)資料
型號(hào): LM2791
廠商: National Semiconductor Corporation
元件分類: LED驅(qū)動(dòng)器
英文描述: Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
中文描述: 電流調(diào)節(jié)開關(guān)電容LED與模擬亮度控制驅(qū)動(dòng)器
文件頁數(shù): 10/11頁
文件大小: 226K
代理商: LM2791
Application Information
(Continued)
BRIGHTNESS CONTROL USING PWM
Brigthness control can be implemented by pulsing a signal at
the SD pin. The recommended signal should be between
100Hz to 1kHz. If the operating PWM frequency is much less
than 100Hz, flicker may be seen in the LEDs. Likewise, if
frequency is much higher, brightness in the LEDs will not be
linear. When a PWM signal is used to drive the SD pin of the
LM2791, connect BRGT pin to a maximun of GND. R
value is selected using the above I
equation as if BRGT
pin is used. The brigthness is controlled by increasing and
decreasing the duty cycle of the PWM. Zero duty cycle will
turn off the brigthness and a 50% duty cycle waveform
produces an average current of 7.5mA if R
is set to
produce a maximum LED current of 15mA. So the LED
current varies linearly with the duty cycle.
PARALLEL Dx OUTPUTS FOR INCREASED CURRENT
DRIVE
Outputs D1 and D2 may be connected together to drive a
single LED. In such a configuration, two parallel current
sources of equal value drive the single LED. R
and
V
should be chosen so that the current through each of
the outputs is programmed to 50% of the total desired LED
current. For example, if 30mA is the desired drive current for
the single LED, R
SET
and V
BRGT
should be selected so that
the current through each of the outputs is 15mA. Connecting
the outputs in parallel does not affect internal operation of
the LM2791and has no impact on the Electrical Character-
istics and limits previously presented. The available Dx out-
put current, maximum Dx voltage, and all other specifica-
tions provided in the Electrical Characteristics table apply to
this parallel output configuration, just as they do to the
standard 2-LED application circuit.
THERMAL PROTECTION
The LM2791 has internal thermal protection circuitry to dis-
able the charge pump if the junction temperature exceeds
150C. This feature will protect the device from damage due
to excessive power dissipation. The device will recover and
operate normally when the junction temperature falls below
the maximum operating junction temperature of 100C. It is
important to have good thermal conduction with a proper
layout to reduce thermal resistance.
POWER EFFICIENCY
An ideal power efficiency for a voltage doubler switched
capacitor converter is given as the output voltage of the
doubler over twice the input voltage as follows:
Efficiency = (V
DIODE
* I
DIODE
) / ( V
IN
* I
DIODE
* Gain) =
V
DIODE
/ 2V
IN
In the case of the LM2791, a more accurate efficiency cal-
culation can be applied as the given formula below.
Efficiency = ((V
D1
* I
D1
) + (V
D2
* I
D2
)) / (I
SUPPLY
* V
IN
)
It is clear that the efficiency will depend on the supply voltage
in the above equation.As such, the lower the supply voltage,
the higher the efficiency.
POWER DISSIPATION
The maximum allowable power dissipation that this package
is capable of handling can be determined as follows:
P
DMax
= (T
JMax
- T
A
) /
θ
JA
where T
is the maximum junction temperature, T
is the
ambient temperature, and
θ
is the junction-to-ambient
thermal resistance of the specified package.
The actual power dissipation of the device can be calculated
using this equation:
P
Dissipation
= (2V
IN
-V
DIODE
)
*
I
LOAD
As an example, if V
in the target application is 4.2V, V
= 3.0V and worse case current consumption is 32mA (16mA
for each diode).
P
Dissipation
= ((2
*
4.2) -3.0)
*
0.032 = 173mW
Power dissipation must be less than that allowed by the
package. Please refer to the Absolute Maximum Rating of
the LM2791.
PCB LAYOUT CONSIDERATIONS
The LLP is a leadframe based Chip Scale Package (CSP)
with very good thermal properties. This package has an
exposed DAP (die attach pad) at the center of the package
measuring 2.0mm x 1.2mm. The main advantage of this
exposed DAP is to offer lower thermal resistance when it is
soldered to the thermal land on the PCB. For PCB layout,
National highly recommends a 1:1 ratio between the pack-
age and the PCB thermal land. To further enhance thermal
conductivity, the PCB thermal land may include vias to a
ground plane. For more detailed instructions on mounting
LLP packages, please refer to National Semiconductor Ap-
plication Note AN-1187.
L
www.national.com
10
相關(guān)PDF資料
PDF描述
LM2791LD-L Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
LM2791LDX-H Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
LM2791LDX-L Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
LM2792LD-H Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
LM2792 Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM2791B WAF 制造商:Texas Instruments 功能描述:
LM2791LD-H 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Current Regulated Switched Capacitor LED Driver with Analog Brightness Control
LM2791LD-H/NOPB 功能描述:IC LED DRIVR WHITE BCKLGT 10-LLP RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動(dòng)器 系列:- 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(dòng)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
LM2791LD-L 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
LM2791LD-L/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