LM3502SQ-35/NOPB National Semiconductor, LM3502SQ-35/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM3502SQ-35/NOPB
• Description: IC LED DRIVR WHITE BCKLGT 16-LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Backlight, White LEDr

Specifications of LM3502SQ-35/NOPB

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 800kHz ~ 1.2MHz
• Voltage - Supply: 2.5 V ~ 5.5 V
• Voltage - Output: 33 V ~ 34 V
• Mounting Type: Surface Mount
• Package / Case: 16-LLP
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 750mA
• Internal Switch(s): Yes
• Efficiency: 80%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3502SQ-35; LM3502SQ-35TR

Application Information
D:
V
V
I
Fs:
L:
INDUCTOR SELECTION
In order to maintain inductance, an inductor used with the
LM3502 should have a saturation current rating larger than
the peak inductor current of the particular application. Induc-
tors with low DCR values contribute decreased power losses
and increased efficiency. The peak inductor current can be
computed for both modes of operation: CCM and DCM.
The cycle-by-cycle peak inductor current for CCM operation
can be computed with:
V
Eff:
Fs:
I
L:
D:
I
∆i
I
The cycle-by-cycle peak inductor current for DCM operation
can be computed with:
V
Fs:
L:
D:
I
The minimum inductance magnitude/inductor value for the
LM3502 can be calculated using the following, which is only
valid when the duty cycle is
OUT
OUT
PEAK
L
PEAK
OUT
IN
IN
IN
(avg): Average Inductor Current.
L
:
:
:
:
: White LED Current/Load Current.
:
: Output Voltage.
:
: Peak Inductor Current.
Duty Cycle for DCM Operation.
Input Voltage.
Switching Frequency.
Inductor Value/Inductance Magnitude.
Input Voltage.
Switching Frequency.
Inductance Magnitude/Inductor Value.
Duty Cycle for DCM Operation.
Input Voltage.
Efficiency of the LM3502.
Switching Frequency.
White LED Current/Load Current.
Inductance Magnitude/Inductor Value.
Duty Cycle for CCM Operation.
Peak Inductor Current.
Inductor Ripple Current.
>
0.5:
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D:
D:
R
V
L:
This equation gives the value required to prevent subhar-
monic oscillations. The result of this equation and the induc-
tor average and ripple current should be accounted for when
choosing an inductor value.
Some recommended inductor manufacturers included but
are not limited to:
CAPACITOR SELECTION
Multilayer ceramic capacitors are the best choice for use
with the LM3502. Multilayer ceramic capacitors have the
lowest equivalent series resistance (ESR). Applied voltage
or DC bias, temperature, dielectric material type (X7R, X5R,
Y5V, etc), and manufacturer component tolerance have an
affect on the true or effective capacitance of a ceramic
capacitor. Be aware of how your application will affect a
particular ceramic capacitor by analyzing the aforemen-
tioned factors of your application. Before selecting a capaci-
tor always consult the capacitor manufacturer’s data curves
to verify the effective or true capacitance in your application.
INPUT CAPACITOR SELECTION
The input capacitor serves as an energy reservoir for the
inductor. In addition to acting as an energy reservoir for the
inductor the input capacitor is necessary for the reduction in
input voltage ripple and noise experienced by the LM3502.
The reduction in input voltage ripple and noise helps ensure
the LM3502’s proper operation, and reduces the effect of the
LM3502 on other devices sharing the same supply voltage.
To ensure low input voltage ripple, the input capacitor must
have an extremely low ESR. As a result of the low input
voltage ripple requirement multilayer ceramic capacitors are
the best choice. A minimum capacitance of 2.0 µF is required
for normal operation, so consult the capacitor manufactur-
er’s data curves to verify whether the minimum capacitance
requirement is going to be achieved for a particular applica-
tion.
OUTPUT CAPACITOR SELECTION
The output capacitor serves as an energy reservoir for the
white LED load when the internal power FET switch (Figure
2: N1) is on or conducting current. The requirements for the
output capacitor must include worst case operation such as
when the load opens up and the LM3502 operates in over-
voltage protection (OVP) mode operation. A minimum ca-
pacitance of 0.5µF is required to ensure normal operation.
Consult the capacitor manufacturer’s data curves to verify
whether the minimum capacitance requirement is going to
be achieved for a particular application.
Some recommended capacitor manufacturers included but
are not limited to:
CoilCraft
IN
DS(ON)
:
: NMOS Power Switch ON Resistance.
Duty Cycle.
1–D.
Input Voltage.
Inductance Magnitude/Inductor Value.
DO1608C-223
DT1608C-223
www.coilcraft.com
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