参数资料
| 型号： | SC410MLTRT |
| 厂商： | Semtech |
| 文件页数： | 18/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 3A 10MLPD |
| 标准包装： | 1 |
| 系列： | EcoSpeed® |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.75 V ~ 7.5 V |
| 输入电压： | 5.5 V ~ 24 V |
| 频率 - 开关： | 200kHz ~ 1MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-VFDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 10-MLPD（3x3） |
| 其它名称： | SC410MLDKR |
SC410
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 reference
tolerance is 1%. Assuming a 1% tolerance from the FB resis-
tor divider, this allows 2% tolerance due to V OUT ripple. Since
this 2% error comes from 1/2 of the ripple voltage, the
allowable ripple is 4%, or 132mV for a 3.3V output.
The maximum ripple current of 2.7A creates a ripple
voltage across the ESR. The maximum ESR value allowed
is shown by the following equations.
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 OUT .
This causes a down-slope or falling di/dt in the 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 LOAD /dt. Peak inductor current is shown
by the next equation.
I LPK = I MAX + 1/2 x I RIPPLEMAX
I LPK = 3A + 1/2 x 2.7A = 4.353A
ESR MAX
2 V RIPPLE
I RIPPLEMAX
ESR MAX = 48.8 m ?
132 mV
2 . 705 A
Rate of change of Load Current
I MAX = maximum load release = 3A
dl LOAD
dt
L 1 L TOL
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
C OUT
Example
I LPK
I LPK I MAX
V OUT d l LOAD
2 V PK V OUT
dt
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.
dl LOAD 2 A
dt 1 s
This causes the output current to move from 3A to 0A in
4.8μs, giving the minimum output capacitance require-
1
L 1 L TOL I OUT I RIPPLE _ PEAK
COUT MIN
2 . 2 H 1 20 %
C OUT
4 . 353 A
2
2
2 2
V PEAK V OUT
Assuming a peak voltage V PEAK of 1.150 (132mV rise upon
load release), and a 6A load release, the required capaci-
tance is shown by the next equation.
ment shown in the following equation.
4 . 353 A
3 . 3 V
2 3 . 432 V 3 . 3 V
C OUT = 33μF
3 A
2 A
1 s
2 . 705 A
COUT MIN
2 . 2 H 1 20 % 3 A
2
3 . 432 V
1
2
3 . 3 V
2
2
Note that C OUT is much smaller in this example, 33μF com-
pared to 56μF based on a worst-case load release. To meet
the worst case design criteria of minimum 56μF, select
three capacitors rated at 22μF and 15m? ESR.
COUT MIN = 56μF
18
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