SC441CTETRT Semtech, SC441CTETRT Datasheet - Page 16

• Manufacturer Part Number: SC441CTETRT
• Description: TVS
• Manufacturer: Semtech

Specifications of SC441CTETRT

• Constant Current: *
• Constant Voltage: *
• Topology: *
• Number Of Outputs: *
• Internal Driver: *
• Type - Primary: *
• Type - Secondary: *
• Frequency: *
• Voltage - Supply: *
• Voltage - Output: *
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Operating Temperature: *
• Current - Output / Channel: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: SC441CTETRTTR

Applications Information (continued)
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 SC441C. 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
Output Capacitor Selection
The next task in SC441C design is targeting the proper
amount of ripple voltage due to the constant-current
LED loads. The two error amplifiers that control the PWM
converter sense the delta between requested current
and actual current in each output current regulator. On
a cycle-by-cycle basis, a small amount of output ripple
ensures good sensing and tight regulation, while the
output current regulators keep each LED current at a fixed
value. Overall, this allows usage of small output caps while
ensuring precision LED current regulation. Although
© 2010 Semtech Corporation
DR74, 4.7μH ~ 15μH
IHLP-2525CZ-01, 4.7μ ~ 10μH
DS85LC, 6.8μH ~ 10μH
I
L
−
peak
=
V
F
IN
S
Inductor
⋅
⋅
L
D
www.cooperet.com
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boundary
. Generally
the mechanics of regulation and frequency dependence
may be complex, actual selection of output capacitor can
be simplified because this capacitor is mainly selected
for the output ripple of the converter. Assume a ceramic
capacitor is used. The minimum capacitance needed for a
given ripple can be estimated by,
V
During load transient, the output capacitor supplies or
absorbs additional current before the inductor current
reaches its steady state value. Larger capacitance helps
with the overshoot and undershoots during load transient,
and loop stability. Recommended ceramic capacitor
manufacturers are listed in Table 3.
Table 3. Recommended Ceramic Capacitor
Manufacturers
Output Rectifying Diode Selection
Schottky diodes are the ideal choice for SC441C due to
their low forward voltage drop and fast switching speed.
Table 4 shows several different Schottky diodes that work
well with the SC441C. Make sure that the diode has a
voltage rating greater that the possible maximum ouput
voltage. The diode conducts current only when the power
switch is turned off. A diode of 2A will be sufficient for
most designs.
Table 4. Recommended Rectifying Diodes
RIPPLE
Kemet
Murata
Taiyo Yuden
C
OUT
V
V
Vendor
I
F
OUT
– Peak to peak output ripple;
S
OUT
IN
– Switching frequency.
Part
SS23
SS24
– Input voltage;
– Output current;
– Boost output voltage;
(V
V
OUT
OUT
F
S
I V
N
V
408-986-0424
814-237-1431
408-573-4150
)
RIPPLE
Phone
I
OUT
www.vishay.com
Vendor
Vishay
www.t-yuden.com
www.murata.com
www.kemet.com
www.semtech.com
Website
SC441C
16