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參數(shù)資料
| 型號(hào)： | HV9903 |
| 廠商： | Supertex, Inc. |
| 元件分類： | LED驅(qū)動(dòng)器 |
| 英文描述： | White LED Driver |
| 中文描述： | 白光LED驅(qū)動(dòng)器 |
| 文件頁(yè)數(shù)： | 5/12頁(yè) |
| 文件大?。?/td> | 326K |
| 代理商： | HV9903 |
fairly low frequency so that the 1ms soft-start interval
does not introduce much error. The R
SET
input is
better for PWM dimming, as it does not include soft-
start. (See below for PWM dimming techniques.)
Soft Start
SHDN
I
IN
50mA/div
I
LED
10mA/div
Open LED Protection
Open LED protection is integrated into the HV9903.
Without open LED protection, output voltage would
climb to destructive levels as the driver attempts to
correct for the open LED condition.
Should the voltage at the SW pin exceed 33V, the
driver latches off and the R
SET
pin is pulled to V
DD
,
indicating a fault condition. To reset the latch, assert
SHDN low for at least 200ns. When SHDN is again
brought high, the driver will be re-enabled, including
soft-start. If the open LED condition persists, the
HV9903 will again latch off.
Inductor Selection
The HV9903 is designed for discontinuous mode
operation. Control loop stability may be compromised
if the converter is allowed to operate in continuous
mode. To assure discontinuous mode operation, the
inductor must not exceed a certain value depending
on supply voltage, output current, and output voltage.
The following graphs show the maximum permissible
inductor value and inductor current rating for a lithium-
ion battery application (2.7V minimum battery
voltage). When calculating LED string voltage drop,
use maximum LED voltage. If using paralleled LED
strings with current balancing resistors, include the
resistor voltage drop in V
LED-STRING
. V
D
is the diode’s
forward voltage drop. Always select the next lower
standard value inductor and be conservative on
inductor rating. Choosing an inductor with lower
resistance results in more efficient operation.
Inductor Value for 2.7V Operation
5mA
10mA
15mA
20mA
25mA
30mA
5V
10V
15V
20V
25V
1 H
10 H
100 H
I
LED
V
LED-STRING
+ (I
LED
· 5
) + V
V
LED-STRING
+ (I
LED
-5
) +V
D
I
Select the next lower standard value,
taking inductor tolerance into account.
Inductor Rating for 2.7V Operation
5V
10V
15V
20V
25V
V
LED-STRING
+ (I
LED
· 5
) + V
D
V
LED-STRING
+ (I
LED
-5
) +V
D
10mA
100mA
1A
P
5mA
10mA
15mA
20mA
25mA
30mA
35mA
40mA
I
LED
Exceeds max recommended SW current
Apply correction factor and select an
inductor with an equal or higher rating.
When selecting the next lower standard value
inductor, the current rating must be adjusted
according to the following equation.
SELECTED
GRAPH
GRAPH
CORRECTED
I
L
L
I
As an example, 4 LEDs with 4V max drop are to be
driven at 20mA. LED string drop is 16V plus 0.6V for
the diode plus 0.1V for LED pin voltage, for a total of
16.7 volts. From the graphs, inductor value at 16.7V
and 20mA is 3.7
μ
H and rating is 320mA. The next
HV9903
HV9903
5
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| HV9903DB1 | 制造商:Supertex Inc 功能描述: |
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