SC2544MLTRT Semtech, SC2544MLTRT Datasheet - Page 10

• Manufacturer Part Number: SC2544MLTRT
• Description: IC CTRL/REG SYNC BUCK 24-MLPQ
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC2544MLTRT

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: Adj to 0.75V
• Frequency - Switching: 100kHz ~ 300kHz
• Voltage - Input: 4.5 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-MLPQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Other names: SC2544MLTR

General Design Pr
General Design Pr
Converter
Converter
General Design Pr
General Design Pr
General Design Procedure f
Converter
Converter
Converter
Selection criterias and design procedures for the fol-
lowing parameters are described:
The following step-down converter specifications are
needed:
Both step-down controllers in the SC2544 operate in
synchronous continuous-conduction mode (CCM)
regardless of the output load level. The output
inductor selection/design is based on the output DC
and transient requirements. Both output current and
voltage ripples are reduced with larger inductance
but it takes longer to change the inductor current
during load transients. Conversely smaller inductance
results in lower DC copper losses but the AC core
losses (flux swing) and the winding AC resistance losses
are higher. A compromise is to choose the inductance
such that peak-to-peak inductor ripple-current is 20%
to 30% of the rated output load current.
Assuming that the inductor current ripple (peak-to-
peak) value is
be
The peak current in the inductor becomes
and the RMS current is
Inductor (L) and Ripple Current
Inductor (L) and Ripple Current
Inductor (L) and Ripple Current
Inductor (L) and Ripple Current
Inductor (L) and Ripple Current
POWER MANAGEMENT
Applications Information (Cont.)
2005 Semtech Corp.
1) Output inductor (L) type and value
2) Output capacitor (C
3) Input capacitor (C
4) Power MOSFETs
5) Current sensing and limiting circuit
6) Voltage sensing circuit
7) Loop compensation network
Input voltage range: V
Input voltage ripple (peak-to-peak): DV
Output voltage: V
Output voltage accuracy: e
Output voltage ripple (peak-to-peak): DV
Nominal output (load) current: I
Maximum output current limit: I
Output (load) current transient slew rate: dI
Circuit efficiency:
*I
(1+
ocedure f
ocedure f
ocedure f
ocedure for a St
L
η
o
o
, the inductance value will then
V
in
o
) type and value
1 (
/2)*Io
o
f I
in,min
) type and value
o
s
D
or a St
or a St
or a St
or a Step-do
)
and V
.
o
o,max
in,max
ep-do
ep-do
ep-do
ep-down P
wn P
wn P
wn P
wn Po o o o o w w w w w er er er er er
in
o
o
(A/ s)
10
Output Capacit
Output Capacit
The followings are to be considered when choosing
inductors.
a) Inductor core material: For higher efficiency
applications above 300 KHz, ferrite, Kool-Mu and
polypermalloy materials should be used. Low-cost
powdered iron cores can be used for cost sensitive-
applications below 300 KHz but with attendant higher
core losses.
b) Select inductance value: Sometimes the calculated
inductance value is not available off-the-shelf. The
designer can choose the adjacent (larger) standard
inductance value. The inductance varies with
temperature and DC current. It is a good engineering
practice to re-evaluate the resultant current ripple
at the rated DC output current.
c) Current rating: The saturation current of the
inductor should be at least 1.5 times of the peak
inductor current under all conditions.
Output Capacit
Output Capacit
Output Capacitor (C
The output capacitor provides output current filtering
in steady state and serves as a reservoir during load
transient. The output capacitor can be modeled as
an ideal capacitor in series with its parasitic ESR and
ESL as shown in Figure 4.
If the current through the branch is i
across the terminals will then be
This basic equation illustrates the effects of ESR,
ESL, and C
Figure 4. An equivalent circuit of output.
v
o
) t (
o
on the output voltage.
Co
V
or (C
or (C
or (C
or (C
o
I
, L
C
rms
1
o o o o o
o
) and V
) and V
) and V
) and V
) and V
0
t
i
I
b
Lesl
o
) t (
1
dt
out
out
out
out
out
12
L
2
esl
.
Ripple
Ripple
Ripple
Ripple
Ripple
di
dt
b
) t (
www.semtech.com
Resr
b
(t), the voltage
SC2544
R
esr
( i
b
). t