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參數(shù)資料
| 型號： | 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 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 487K |
| 代理商： | LM2794TL |
Application Information
(Continued)
Output resistance results in droop in the P
voltage pro-
portional to the amount of current delivered by the pump.
The P
voltage is an important factor in determining the
total output current capability of an application. Taking total
output current to be the sum of all D
X
output currents plus
the current delivered through the P
pin, the voltage at
P
OUT
can be predicted with the following equations:
I
TOTAL
= I
D1
+ I
D2
+ I
D3
+ I
D4
+ I
POUT
V
POUT
= 1.5 x V
IN
I
TOTAL
x R
OUT
LED HEADROOM VOLTAGE (V
HR
)
Four current sources are connected internally between P
OUT
and D
1
-D
4
. The voltage across each current source, (V
POUT
V
DX
), is referred to as headroom voltage (V
HR
). The cur-
rent sources require a sufficient amount of headroom voltage
to be present across them in order to regulate properly.
Minimum required headroom voltage is proportional to the
current flowing through the current source, as dictated by the
equation:
V
HR-MIN
= k
HR
x I
DX
The parameter k
, typically 20mV/mA in the LM2794/5, is a
proportionality constant that represents the ON-resistance of
the internal current mirror transistors. For worst-case design
calculations, using a k
of 25mV/mA is recommended.
(Worst-case recommendation accounts for parameter shifts
from part-to-part variation and applies over the full operating
temperature range).
Figure 3
shows how output current of
the LM2794/5 varies with respect to headroom voltage.
On the flat part of the graph, the currents regulate properly
as there is sufficient headroom voltage for regulation. On the
sloping part of the graph the headroom voltage is too small,
the current sources are squeezed, and their current drive
capability is limited. Changes in headroom voltage from one
output to the next, possible with LED forward voltage mis-
match, will result in different output currents and LED bright-
ness mismatch. Thus, operating the LM2794/5 with insuffi-
cient headroom voltage across the current sources should
be avoided.
20028535
FIGURE 2. Keypad LEDs Connected to P
OUT
20028539
FIGURE 3. I
LED
vs V
HR
4 LEDs, V
IN
= 3.0V
L
www.national.com
12
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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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