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參數(shù)資料
| 型號(hào)： | LM3590 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | LED驅(qū)動(dòng)器 |
| 英文描述： | LM3590Series White LED Driver |
| 中文描述： | LM3590Series白光LED驅(qū)動(dòng)器 |
| 文件頁(yè)數(shù)： | 7/9頁(yè) |
| 文件大?。?/td> | 205K |
| 代理商： | LM3590 |
Application Information
CIRCUIT DESCRIPTION
The LM3590 is a constant current series White-LED Driver,
providing up to 20mA from an input voltage between 7.5V to
12.6V. To set the LED drive current, the LM3590 uses a
resistor connected to the I
SET
pin to set a reference current.
This reference current is then multiplied and mirrored to the
constant current output, I
OUT
. The LED brightness can be
controlled by applying a PWM (Pulse Width Modulation)
signal to the Enable pin (EN). (see
PWM BRIGHTNESS
CONTROL PROCEDURES
section).
ENABLE MODE
The Enable pin (EN) disables the part and reduces the
quiescent current to 0.1μA(typ.). The LM3590 has an active-
high enable pin (LOW = shut down, HIGH = operating). The
LM3590 EN pin can be driven with a low-voltage CMOS logic
signal (1.5V logic, 1.8V logic, etc). There is an internal
500k
pull-down between the EN and GND pins of the
LM3590.
CAPACITOR SELECTION
Although not required for normal operation, a capacitor can
be added to the voltage input of the LM3590 to reduce line
noise.
A
surface-mount
multi-layer
(MLCC) is recommended. MLCCs are small, inexpensive
and have very low equivalent series resistance (ESR,
≤
15m
typ.). MLCCs with a X5R or X7R temperature char-
acteristic are preferred for use with the LM3590.
Table 1.
Ceramic Capacitor Manufacturers
lists suggested capacitor
suppliers for the typical application circuit.
ceramic
capacitor
TABLE 1. Ceramic Capacitor Manufacturers
Manufacturer
TDK
Murata
Taiyo Yuden
Contact
www.component.tdk.com
www.murata.com
www.t-yuden.com
LED SELECTION
The LM3590 is designed to drive up to 3 LEDs with the
combined forward voltages of the LEDs being no greater
than 11.5V, when using a 12V input supply. The typical and
maximum diode forward voltage depends highly on the
manufacturer and their technology.
Table 2. White LED Se-
lection
lists two suggested manufacturers. LED Forward cur-
rent matching is guaranteed by design, due to the series
LED configuration of the LM3590.
TABLE 2. White LED Selection
Manufacturer
Osram
Nichia
Contact
www.osram-os.com
www.nichia.com
LED HEADROOM VOLTAGE (V
HR
)
A single current source is connected internally between V
IN
and I
OUT
. The voltage across the current source, (V
IN
V
), is referred to as headroom voltage (V
). The cur-
rent source requires a sufficient amount of headroom voltage
to be present across it in order to regulate properly. Minimum
required headroom voltage is proportional to the current
flowing through the current source, as dictated by the equa-
tion:
V
HR-MIN
= k
HR
x I
OUT
The parameter k
HR
, typically 15mV/mA in the LM3590, is a
proportionality constant that represents the ON-resistance of
the internal current mirror transistors. For worst-case design
calculations, using a k
HR
of 20mV/mA is recommended.
(Worst-case recommendation accounts for parameter shifts
from part-to-part variation and applies over the full operating
temperature range).
Figure 1
shows how output current of
the LM3590 varies with respect to headroom voltage.
On the flat part of the graph, the current is regulated properly
as there is sufficient headroom voltage for regulation. On the
sloping part of the graph the headroom voltage is too small,
the current source is squeezed, and the current drive capa-
bility is limited. Thus, operating the LM3590 with insufficient
headroom voltage across the current source should be
avoided.
I
SET
PIN
An external resistor, R
, connected to the I
pin sets the
output current. The internal current mirror sets the series
LED output current with a 100:1 ratio to the current through
R
. The current matching through each LED is guaranteed
by the series LED drive topology. The following equation
approximates the LED current:
I
OUT
= 100 x (1.25V ÷ R
SET
) (Amps)
PWM BRIGHTNESS CONTROL PROCEDURES
The brightness of the LEDs can be linearly varied from zero
up to the maximum programmed current level by applying a
Pulse-Width-Modulated signal to the EN pin of the LM3590.
The following procedures illustrate how to program the LED
drive current and adjust the output current level using a
PWM signal.
1.
Determine the maximum desired I
OUT
current. Use the
I
OUT
equation to calculate R
SET
20081312
FIGURE 1. I
OUT
vs V
HR
V
HR
= V
IOUT
V
IN
= 12.0V
L
www.national.com
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