LM3401EVAL National Semiconductor, LM3401EVAL Datasheet - Page 4

• Manufacturer Part Number: LM3401EVAL
• Description: BOARD EVALUATION FOR LM3401
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3401EVAL

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Features: Dimmable
• Voltage - Input: 4.5 ~ 35V
• Utilized Ic / Part: LM3401
• Kit Contents: Board
• Svhc: No SVHC (15-Dec-2010)
• Kit Features: Hysteretic Control For Speed And
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Voltage - Output: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed

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LED String Options
The default LED current setting is 340 mA, typical of many
1W LEDs. To adjust this value, the current setting resistor,
R1, can be changed according to Table 1. For other values,
use the equation below:
R1 must be rated to handle the power dissipation of the LED
current. For example, in steady state R1 will dissipate
(0.340
power rating would be appropriate.
The LM3401 can also drive LED currents in excess of 1A. For
these applications a larger pad is provided for a higher current
PFET. An example BOM for a typical 3.5A application is
shown in Table 4. The switching frequency, ripple current, and
current limit values will depend on the number and type of
# of series
LEDs
2
x 0.59) = 68 mW, indicating that a resistor with a 1/8W
1
2
3
4
1
2
1
FIGURE 9. Efficiency vs Input Voltage
Driving 700 mA and 1A LEDs
Osram golden dragon
Osram golden dragon
Luxeon K2 Emitter
Luxeon V Star
Luxeon V Star
Luxeon Star
Luxeon Star
LED Type
TABLE 3. Typical Operating Conditions (* = at 24Vin)
Average LED
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current
340 mA
340 mA
340 mA
340 mA
700 mA
700 mA
1A
4
The LM3401 demo board can drive a wide variety of LEDs.
Ripple current and switching frequency will vary with the LED
forward voltage, number of LEDs, and input voltage. Table
3 shows the typical results for some common LED strings
when using the Table 1 settings at an input voltage of 24V.
Typical switching frequency vs input voltage is shown in Fig-
ure 5.
For some LED strings, the demo board settings given in Table
1 may not be appropriate. For example, where the switching
frequency increases above the 1.5 MHz maximum or where
LED ripple current is higher than the maximum LED rating. In
this case, refer to the LM3401 datasheet to modify the demo
board as needed.
LEDs installed, as well as the selected PFET. A low Vgs
threshold PFET is recommended for higher current applica-
tions, as the initial HG voltage will decrease somewhat when
driving PFETs with a larger gate capacitance. Refer to the
LM3401 datasheet for detailed design information.
425 kHz
655 kHz
800 kHz
845 kHz
415 kHz
500 kHz
230 kHz
* Freq.
FIGURE 10. Maximum Contrast Ratio vs
Dimming Frequency (100:1 = 1% duty)
* p-p ripple
110 mA
110 mA
110 mA
110 mA
190 mA
190 mA
280 mA
Minimum VIN
10.4V
13.8V
14.5V
4.5V
7.0V
7.0V
4.5V
30025410