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參數(shù)資料
| 型號(hào)： | RT9271 |
| 英文描述： | Step-up DC/DC Converter |
| 中文描述： | 升壓型DC / DC轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 9/12頁(yè) |
| 文件大?。?/td> | 386K |
| 代理商： | RT9271 |
Preliminary
RT9271
DS9271-01 July 2003
www.richtek.com
9
Application Note
LED Current Control
The LED current is controlled by the feedback resistor
(R2 in Application Circuit). The feedback reference is
0.25V. The LED current is 0.25V/R2. In order to have
accurate LED current, precision resistors are preferred
(1% is recommended). The formula and table for R2
selection are shown below.
R2 = 0.25V/I
LED
R2 Resistor Value Selection
ILED (mA)
5
10
12
15
20
Recommended Inductance (for Li-Ion cell)
Condition
1 WLED
2 WLEDs
3 WLEDs
4 WLEDs
R2 (
)
49.9
24.9
21
16.5
12.4
Inductance (μH)
10
4.7
6.8
4.7
Layout Guide
A full GND plane without gap break.
V
CC
to GND noise bypass – Short and wide
connection for the 1
μ
F MLCC capacitor between
Pin6 and Pin2.
Minimized LX node copper area to reduce EMI.
Minimized FB node copper area and keep far away
from noise sources.
Board Layout Example (2-Layer EVB Board)
(Refer to EVB Circuit)
-
Top Layer –
- Bottom Layer -
EVB Circuit
Vin
VCC
CE
GND
LX
FB
C2
D1
R2
OVP
D2
D5
D4
D3
+
C5
C1
C3
C4
R1
L1
S3
S2
S1
RT9271
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