SC440MLTRT Semtech, SC440MLTRT Datasheet - Page 14

• Manufacturer Part Number: SC440MLTRT
• Description: IC LED DRVR WHITE BCKLGT 24-MLPQ
• Manufacturer: Semtech
• Type: Backlight, White LEDr

Specifications of SC440MLTRT

• Constant Current: Yes
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Backlight
• Frequency: 640kHz ~ 960kHz
• Voltage - Supply: 4.5 V ~ 21 V
• Voltage - Output: 40V
• Mounting Type: Surface Mount
• Package / Case: 24-MLPQ
• Current - Output / Channel: 30mA
• Internal Switch(s): Yes
• Efficiency: 91%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Operating Temperature: -
• Other names: SC440MLTR

Applications Information (continued)
to GND can help prevent the SC440 from entering the
false protection, or, simply disable this feature by tying
Pin 15 to GND.
Parallel Operation
When two or more SC440s are operating in parallel for
a large-sized panel application, audible noise may be
observed due to a non-synchronous switching frequency.
The ripple voltage on the input voltage rail will be
modulated by the beat frequency resulting in audible
noise. This situation can be resolved by adding an input
inductor between the input voltage rail and the VIN pin.
This situation can also be improved by adding more input
decoupling capacitors.
Inductor Selection
The inductance value of the inductor affects the converter’s
steady state operation, transient response, and its loop
stability. Special attention needs to be paid to three
specifications of the inductor, its value, its DC resistance
and saturation current. The inductor’s inductance value
also determines the inductor ripple current. The converter
can operate in either CCM or DCM depending on its
working conditions. The inductor DC current or input
current can be calculated as,
I
Then the duty ratio is,
V
diode
© 2010 Semtech Corp.
IN
D
- Input current;
– Forward conduction drop of the output rectifying
I
V
V
OUT
OUT
IN
– Efficiency of the boost converter.
– Input voltage;
– Output current;
– Boost output voltage;
NOT RECOMMENDED FOR NEW DESIGNS: SEE SC440A
When the boost converter runs in DCM ( L < L
takes the advantages of small inductance and quick
transient response while avoiding the bandwidth-
limiting instability of the RHP zero found in CCM boost
converters.
The inductor peak current is,
The converter will work in CCM if L > L
the converter has higher efficiency under CCM and the
inductor peak current is,
For many applications, an inductor with value of 4.7µH to
22µH should be fine, such as for the typical case shown
on page 1. The inductor peak current must be less than its
saturation rating. When the inductor current is close to the
saturation level, its inductance can decrease 20% to 35%
from the 0A value depending on the vendor specifications.
Using a small value inductor forces the converter under
DCM in which case the inductor current ramps down to
zero before the end of each switching cycle. It reduces the
boost converter’s maximum output current, and produces
large input voltage ripple. An inductor with larger
inductance will reduce the bandwidth of the feedback
loop, possibly higher DC resistance (DCR). Inductor’s DCR
plays a significant role for the total efficiency since the
power transistor is integrated inside the SC440. Of course,
there is a trade-off between the DCR and inductor size.
Table 2 lists recommended inductors and their vendors.
Table 2. Recommended Inductors
DR74, 4.7μH ~ 15μH
IHLP-2525CZ-01, 4.7μ ~ 10μH
DS85LC, 6.8μH ~ 10μH
I
L
−
peak
=
V
F
IN
S
Inductor
⋅
⋅
L
D
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boundary
. Generally
SC440
boundary
), it
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