LM3519MKEV National Semiconductor, LM3519MKEV Datasheet - Page 5

• Manufacturer Part Number: LM3519MKEV
• Description: BOARD EVALUATION LM3519MK
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3519MKEV

• Current - Output / Channel: 20mA
• Outputs And Type: 1, Non-Isolated
• Features: Dimmable
• Voltage - Input: 2.7 ~ 5.5V
• Utilized Ic / Part: LM3519
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Voltage - Output: -

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 (I
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
PEAK
of inductor) based on the
5
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.
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