LM3410XSDLEDEV National Semiconductor, LM3410XSDLEDEV Datasheet - Page 9

• Manufacturer Part Number: LM3410XSDLEDEV
• Description: BOARD EVAL LM3410 BOOST LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3410XSDLEDEV

• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3 ~ 24V
• Features: Thermal Shutdown Protection
• Voltage - Input: 2.7 ~ 5.5V
• Utilized Ic / Part: LM3410
• Kit Contents: Board, Datasheet
• Svhc: No SVHC (15-Dec-2010)
• Kit Features: Converts 2.7V To 5.5V Input And Illuminates Five 50 MA LEDs In Series Using The LM3410X
• Mcu Supported Families: LM3410
• Rohs Compliant: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output / Channel: -

The Duty Cycle (D) for a Boost converter can be approximat-
ed by using the ratio of output voltage (V
(V
Therefore:
Power losses due to the diode (D1) forward voltage drop, the
voltage drop across the internal NMOS switch, the voltage
drop across the inductor resistance (R
losses must be included to calculate a more accurate duty
cycle (See Calculating Efficiency and Junction Tempera-
ture for a detailed explanation). A more accurate formula for
calculating the conversion ratio is:
Where η equals the efficiency of the LM3410 application.
Or:
Therefore:
IN
).
OUT
DCR
) to input voltage
) and switching
FIGURE 5. Inductor Current
9
Inductor ripple in a LED driver circuit can be greater than what
would normally be allowed in a voltage regulator Boost &
Sepic design. A good design practice is to allow the inductor
to produce 20% to 50% ripple of maximum load. The in-
creased ripple shouldn’t be a problem when illuminating
LEDs.
From the previous equations, the inductor value is then ob-
tained.
Where
One must also ensure that the minimum current limit (2.1A)
is not exceeded, so the peak current in the inductor must be
calculated. The peak current (Lpk I) in the inductor is calcu-
lated by:
When selecting an inductor, make sure that it is capable of
supporting the peak input current without saturating. Inductor
saturation will result in a sudden reduction in inductance and
prevent the regulator from operating correctly. Because of the
speed of the internal current limit, the peak current of the in-
ductor need only be specified for the required maximum input
current. For example, if the designed maximum input current
is 1.5A and the peak current is 1.75A, then the inductor should
be specified with a saturation current limit of >1.75A. There is
no need to specify the saturation or peak current of the in-
ductor at the 2.8A typical switch current limit.
Because of the operating frequency of the LM3410, ferrite
based inductors are preferred to minimize core losses. This
presents little restriction since the variety of ferrite-based in-
ductors is huge. Lastly, inductors with lower series resistance
(DCR) will provide better operating efficiency. For recom-
mended inductors see Example Circuits.
INPUT CAPACITOR
An input capacitor is necessary to ensure that V
drop excessively during switching transients. The primary
specifications of the input capacitor are capacitance, voltage,
RMS current rating, and ESL (Equivalent Series Inductance).
The recommended input capacitance is 2.2 µF to 22 µF de-
pending on the application. The capacitor manufacturer
specifically states the input voltage rating. Make sure to check
any recommended deratings and also verify if there is any
significant change in capacitance at the operating input volt-
I
Lpk
= I
IN
+ ΔI
1/T
L
or I
S
Lpk
= f
30038519
SW
= I
OUT
/D' + Δi
L
www.national.com
IN
does not