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PDF LM3519 Data sheet ( Hoja de datos )
| Número de pieza | LM3519 | |
| Descripción | High Frequency Boost White LED Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM3519 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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September 2005
LM3519
High Frequency Boost White LED Driver with
High-Speed PWM Brightness Control
General Description
The LM3519 drives up to 4 white LEDs with constant current
to provide LCD backlighting in handheld devices. The LED
current is internally set to 20mA. The series connection
allows the LED current to be identical for uniform brightness
and minimizes the number of traces to the LEDs. Brightness
control is achieved by applying a PWM signal on enable with
frequencies up to 30kHz.
The LM3519 features a proprietary PFM regulation architec-
ture with switching frequencies between 2MHz to 8MHz,
minimizing inductor size.
Over-voltage protection circuitry and high frequency opera-
tion permit the use of low-cost small output capacitors. Dur-
ing shutdown, the output is disconnected from the input in
order to avoid leakage current path through the LEDs to
ground.
The LM3519 is available in a tiny 6-pin SOT23 package.
Features
n Drives 2 to 4 LEDs at 20mA
n Up to 30kHz PWM Dimming Control Capability
n >80% Peak Efficiency
n Up to 8MHz Switching Frequency
n Small External Components: 1µH - 3.3µH(typ.2.2µH)
Inductor and 1µF Output Capacitor
n True Shutdown Isolation
n Over-Voltage Protection
n Wide Input Voltage Range: 2.7V to 5.5V
n Small Footprint SOT23-6 Package
Applications
n LCD, White LED Backlighting on Mobile Phones
n Digital Still Cameras and PDAs
n General Purpose LED Lighting in Handheld Devices
Typical Application
20160201
FIGURE 1. Typical Application Circuit
© 2005 National Semiconductor Corporation DS201602
www.national.com
1 page  
Circuit Description
The LM3519 is a step-up converter for white LED applica-
tions that uses a unique and proprietary pulse frequency
modulation (PFM) architecture to optimize high efficiency at
high frequency operation. Unlike most PFM architecture
implementations, the LM3519’s unique architectural imple-
mentation results in non-pulse skipping variable frequency
operation. The regulator is forced to operate at the edge of
Continous Conduction Mode (CCM). The error amplifier will
set the end of the on-time (IPEAK of inductor) based on the
load (LEDs) current. During this operation, the inductor cur-
rent ramps up and reaches a peak current at end of the
on-time. At this point, the internal power switch is turned off
until the inductor current reaches zero, and the cycle repeats
again. The switching frequency is set based on the charge
(on-time) and discharge(off-time) of the inductor current. The
frequency can range between 2MHz to 8MHz over the op-
erating input range.
The LM3519 operation can be best understood through an
examination of the block diagram in Figure 2. When LED
current is out of regulation, the LED_rtn voltage falls below
or rises above the internal reference voltage (VREF). The
error amplifier will output a signal to increase or decrease the
proper on-time duration of N1 power FET. This correction
allows the inductor’s stored energy to increase or decrease
to a sufficient level that when transferred to the load will bring
the LED_rtn current back into regulation.
During steady-state operation for a typical switching cycle,
the oscillator sets the driver logic and turns on N1 power
device. N1 conducts current through the inductor and re-
verse biases the external diode. The LED current is supplied
by the output capacitor when N1 is conducting. Once N1
on-time period is concluded, the internal power device is
turned off and the external diode is forward baised. The
inductor current then flows through the diode to the LED load
to replenish the output capacitor and keep the LED current
regulated at the trimmed target.
5 www.national.com
5 Page 
Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7µF and
COUT = 1µF, L = 2.2µH and 4 LEDs. TA = +25˚C, unless otherwise stated.) (Continued)
Typical Switching Waveform
(VIN = 3.6V, 4LEDs, 3.3µH)
Typical Switching Waveform
(VIN = 3.6V, 4LEDs, 2.2µH)
Typical Switching Waveform
(VIN = 3.6V, 3LEDs, 2.2µH)
20160218
Typical Switching Waveform
(VIN = 3.6V, 2LEDs, 2.2µH)
20160212
Typical Switching Waveform
(VIN = 3.6V, 3LEDs, 1µH)
20160214
Typical Switching Waveform
(VIN = 3.6V, 4LEDs, 1µH)
20160215
20160228
11
20160229
www.national.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LM3519.PDF ] | |
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