SC414MLTRT Semtech, SC414MLTRT Datasheet - Page 23

• Manufacturer Part Number: SC414MLTRT
• Description: IC BUCK SYNC ADJ 6A 28MLPQ
• Manufacturer: Semtech
• Series: SmartDrive™r
• Type: Step-Down (Buck)r

Specifications of SC414MLTRT

• Mfg Application Notes: SC414 Basic Design Procedure
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.75 ~ 5.5 V
• Current - Output: 6A
• Frequency - Switching: 200kHz ~ 1MHz
• Voltage - Input: 3 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-MLPQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC414MLTR

Applications Information (continued)
Capacitor Selection
The output capacitors are chosen based on required ESR
and capacitance. The maximum ESR requirement is con-
trolled by the output ripple requirement and the DC toler-
ance. The output voltage has a DC value that is equal to
the valley of the output ripple plus 1/2 of the peak-to-peak
ripple. Change in the output ripple voltage will lead to a
change in DC voltage at the output.
The design goal is for the output voltage regulation to be
±4% under static conditions. The internal 750mV refer-
ence tolerance is 1%. Assuming a 1% tolerance from the
FB resistor divider, this allows 2% tolerance due to V
ripple. Since this 2% error comes from 1/2 of the ripple
voltage, the allowable ripple is 4%, or 40mV for a 1V
output.
The maximum ripple current of 2.53A creates a ripple
voltage across the ESR. The maximum ESR value allowed
is shown by the following equations.
The output capacitance is chosen to meet transient
requirements. A worst-case load release, from maximum
load to no load at the exact moment when inductor
current is at the peak, determines the required capaci-
tance. If the load release is instantaneous (load changes
from maximum to zero in < 1μs), the output capacitor
must absorb all the inductor’s stored energy. This will
cause a peak voltage on the capacitor according to the
following equation.
I
I
ESR
ESR
COUT
RIPPLE
RIPPLE
MAX
MAX
_
MIN
VINMIN
(
= 15.8 mΩ
V
IN
I
RIPPLEMAX
L
V
RIPPLE
I
(
V
OUT
10
V
L
OUT
PEAK
8 .
)
2
1
1
1
T
5 .
2
. 2
40
V
ON
I
RIPPLEMAX
53
)
mV
H
V
OUT
A
311
ns
2
2
. 2
03
A
OUT
Assuming a peak voltage V
load release), and a 6A load release, the required capaci-
tance is shown by the next equation.
If the load release is relatively slow, the output capacitance
can be reduced. At heavy loads during normal switching,
when the FB pin is above the 750mV reference, the DL
output is high and the low-side MOSFET is on. During this
time, the voltage across the inductor is approximately
-V
inductor. If the load di/dt is not much faster than the
-di/dt in the inductor, then the inductor current will tend
to track the falling load current. This will reduce the excess
inductive energy that must be absorbed by the output
capacitor, therefore a smaller capacitance can be used.
The following can be used to calculate the needed capaci-
tance for a given dI
by the next equation.
Example
OUT
COUT
COUT
I
I
I
Rate
C
dl
LPK
LPK
MAX
. This causes a down-slope or falling di/dt in the
OUT
LOAD
dt
= I
= 6A + 1/2 x 2.53A = 7.26A
= maximum load release = 6A
of
MIN
MIN
MAX
I
LPK
change
. 1
= 772μF
+ 1/2 x I
1
25
1
s
5 .
L
A
LOAD
H
2
V
. 1
I
of
LPK
OUT
/dt. Peak inductor current is shown
V
05
6
RIPPLEMAX
PK
Load
A
V
PEAK
dl
2
V
1
2
I
MAX
LOAD
OUT
Current
of 1.150 (100mV rise upon
1
. 2
V
SC414/SC424
53
2
dt
A
2
dl
LOAD
dt
23