LM5022LEDEVAL National Semiconductor, LM5022LEDEVAL Datasheet - Page 2

• Manufacturer Part Number: LM5022LEDEVAL
• Description: BOARD EVALUATION FOR LM5022
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5022LEDEVAL

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 40V
• Features: Dimmable
• Voltage - Input: 10 ~ 14V
• Utilized Ic / Part: LM5022
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Powering The Converter
The input voltage should be connected between the VIN and
GND terminals on the left side of the board. The series-con-
nected chain of LEDs should be connected between the LED
Enabling The Converter
Once the input voltage has risen above the UVLO threshold
of 9.0V the OFF* terminal controls the state of the converter.
The LM5022 is disabled whenever the OFF* terminal is
grounded. The LM5022 is enabled whenever the OFF* ter-
minal is open-circuited. Upon enabling the LM5022 will per-
form a soft-start, after which the output supplies constant
current to the LEDs.
PWM Dimming
The light output of LED arrays is often controlled or reduced
with a PWM signal applied to the output current. This dimming
method allows the converter to operate at a specific output
current level (usually a set point determined by the LED man-
ufacturer) instead of adjusting the average output current.
The LM5022 boost LED evaluation board provides the DIM
terminal as an input for PWM signals. DIM connects to the
gate of a small MOSFET, Q3, that short-circuits or open-cir-
cuits the COMP pin of the LM5022. When the voltage at
DIM is logic high, the converter output current is off. When the
voltage at DIM is logic low, the converter output current is on.
Output Open-Circuit Protection
The zener diode D2 provides protection in the case of an out-
put open circuit. This can happen if the LED chain is discon-
nected or one of the LEDs fails as an open circuit while the
LM5022 is powered. Open circuit is the most common LED
failure mode, and it effectively disconnects the feedback path
FIGURE 3. LED Connector
2
+ and LED- terminals or using connector J1 as shown in Fig-
ure 3. Solid 18 or 20 gauge wire with about 1 cm of insulation
stripped away makes a convenient solderless connection to
J1.
of the converter. Without protection a boost regulator-based
LED driver would attempt to drive the output voltage beyond
the limits of the external components. With D2 in the place,
any output open circuit causes the output voltage to equal the
breakdown of the zener diode plus the system feedback volt-
age of 1.25V. The minimum zener breakdown voltage should
therefore be just higher than the maximum LED array voltage.
For the example circuit, the minimum zener breakdown is
44.6V, providing a total output voltage of 46V or higher. Re-
sistor Rfb1 limits the zener current to approximately 1 mA.
MOSFET Footprints
The LM5022 boost LED evaluation board has a footprint for
a single N-channel MOSFET with an SO-8 package using the
industry standard pinout. (See Figure 4) This footprint can al-
so accept thermally enhanced MOSFET packages that are
compatible with SO-8 footprints.
FIGURE 4. SO-8 MOSFET Pinout
30013303
30013304