LM3407EVAL National Semiconductor, LM3407EVAL Datasheet - Page 4

• Manufacturer Part Number: LM3407EVAL
• Description: BOARD EVALUATION FOR LM3407
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3407EVAL

• Current - Output / Channel: 350mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 4.5V
• Features: Dimmable
• Voltage - Input: 4.5 ~ 30V
• Utilized Ic / Part: LM3407
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Design Procedure
CONNECTING TO LED ARRAY
The LM3407 evaluation board features a female 6-pin SIP
connector J1 for board-to-board connection of the LED array.
Figure 5 shows the pin-out of J1. To avoid damaging the
SETTING THE LED CURRENT
The output current of the evaluation board is adjustable by
changing the current setting resistors RISNS1 and RISNS2.
By default, the value of both RISNS1 and RISNS2 is 1.13Ω
at 1% tolerance, which results in a resistance of 0.565Ω. This
value of R
value of R
When selecting the value of the current setting resistors
(RISNS1 and RISNS2), it is important to ensure the rated
powers of the resistors are not exceeded. For example, when
I
and RISNS2 in steady state is 0.35 mA
equals 69 mW, indicating a resistor of 1/8W power rating is
appropriate.
OUT
is set at 350mA, the total power dissipation on RISNS1
ISNS
ISNS
can be calculated by using the equation:
sets the output current (I
FIGURE 5. Connecting an LED Array to the LM3407 Evaluation Board
OUT
2
) at 350 mA. The
x 0.565Ω, which
4
components, do not connect the LED array with incorrect po-
larity or alter the connections of the LED array when the
evaluation board is connected to power. It is highly recom-
mended to attach the LED array to a heat sink for heat
dissipation and to apply force ventilation to the LED array as
necessary.
SETTING THE SWITCHING FREQUENCY
The switching frequency of the LM3407 evaluation board is
programmable by adjusting the value of the frequency setting
resistor RFS. The default value of the RFS pre-installed on
the evaluation board is 40.2 kΩ, at which the switching fre-
quency is 1MHz. In order to guarantee good current regula-
tion, it is suggested to set the switching frequency between
300KHz and 1MHz. The switching frequency is calculated by
the expression shown below:
for 40kΩ
For the convenience of selecting the value of RFS, a selection
chart of f
SW
≤
RFS
against RFS is provided:
≤
150 kΩ
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