LM3410YMY/NOPB National Semiconductor, LM3410YMY/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM3410YMY/NOPB
• Description: IC LED DRVR WT/OLED BCKLT 8-MSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Backlight, OLED, White LEDr

Specifications of LM3410YMY/NOPB

• Constant Current: Yes
• Topology: PWM, SEPIC, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight, Flash/Torch
• Type - Secondary: High Brightness LED (HBLED), OLED, White LED
• Frequency: 360kHz ~ 680kHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 3 V ~ 24 V
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP Exposed Pad, 8-HMSOP, 8-eMSOP
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 2.8A
• Internal Switch(s): Yes
• Efficiency: 88%
• Led Driver Application: Backlighting, LED Flash Driver
• No. Of Outputs: 1
• Output Current: 1.5A
• Output Voltage: 24V
• Input Voltage: 2.7V To 5.5V
• Dimming Control Type: PWM
• Rohs Compliant: Yes
• For Use With: LM3410XSDSEPEV - BOARD EVALUATION FOR LM3410
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3410YMY

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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:
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.
IN
).
FIGURE 5. Inductor Current
OUT
DCR
) to input voltage
) and switching
30038519
10
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-
age and the operating temperature. The ESL of an input
capacitor is usually determined by the effective cross sec-
tional area of the current path. At the operating frequencies
of the LM3410, certain capacitors may have an ESL so large
that the resulting impedance (2
required to provide stable operation. As a result, surface
mount capacitors are strongly recommended. Multilayer ce-
ramic capacitors (MLCC) are good choices for both input and
output capacitors and have very low ESL. For MLCCs it is
recommended to use X7R or X5R dielectrics. Consult capac-
itor manufacturer datasheet to see how rated capacitance
varies over operating conditions.
OUTPUT CAPACITOR
The LM3410 operates at frequencies allowing the use of ce-
ramic output capacitors without compromising transient re-
sponse. Ceramic capacitors allow higher inductor ripple
without significantly increasing output ripple. The output ca-
pacitor is selected based upon the desired output ripple and
transient response. The initial current of a load transient is
provided mainly by the output capacitor. The output
impedance will therefore determine the maximum voltage
perturbation. The output ripple of the converter is a function
I
Lpk
= I
IN
+ ΔI
1/T
L
or I
S
Lpk
= f
π
SW
= I
fL) will be higher than that
OUT
/D' + Δi
L
IN
does not