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參數資料
| 型號： | SC418ULTRT |
| 廠商： | Semtech |
| 文件頁數： | 16/30頁 |
| 文件大小： | 691K |
| 描述： | IC REG DL BUCK/LINEAR 20MLPQ |
| 產品培訓模塊： | Power Supplies 101 |
| 標準包裝： | 1 |
| 系列： | EcoSpeed® |
| 拓撲： | 降壓（降壓）（1），線性（LDO）（1） |
| 功能： | 任何功能 |
| 輸出數： | 2 |
| 頻率 - 開關： | 1MHz |
| 電壓/電流 - 輸出 1： | 控制器 |
| 電壓/電流 - 輸出 2： | 0.75 V ~ 5.25 V，200mA |
| 帶 LED 驅動器： | 無 |
| 帶監控器： | 無 |
| 帶序列發生器： | 無 |
| 電源電壓： | 3 V ~ 28 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 20-MLPQ |
| 供應商設備封裝： | 20-MLPQ（3x3） |
| 包裝： | 標準包裝 |
| 其它名稱： | SC418ULTRTDKR |
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SC418
6
FB Ripple
Voltage (V
FB
)
FB threshold
(500mV)
Inductor
Current
DH
DL
(0A)
minimum frequency
After the programmable time-out, DL drives
high if V
FB
has not reached the FB threshold.
DH On-time is triggered when
V
FB
reaches the FB Threshold
On-time
(T
ON
)
programmable time-out
Figure 5 Ultrasonic Power-Save Operation
The equation for determining the R
PSV
resistor value is
shown next. The desired minimum frequency is f
SWMIN
.
SWMIN
PSV
f
pF
350
1
R
Power-Save Mode Operation
The device provides power-save operation at light loads
with no minimum operating frequency, selected by float-
ing the PSV pin (no connection). In this mode of opera-
tion, the zero cross comparator monitors inductor current
via the voltage across the low-side MOSFET during the
off-time. If the inductor current falls to zero for 8 consecu-
tive switching cycles, the controller enters power-save
operation. It will then turn off the low-side MOSFET on
each subsequent cycle, provided that the current crosses
zero. After the low-side MOSFET is off, both high-side and
low-sides MOSFETs remain off until V
FB
drops to the 500mV
threshold. While the MOSFETs are off the load is supplied
by the output capacitor. If the inductor current does not
reach zero on any switching cycle, the controller immedi-
ately exits power-save and returns to forced continuous
mode. Figure 6 shows power-save operation at light
loads.
FB Ripple
Voltage
(V
FB
)
FB threshold
DL
DH
Inductor
Current
Zero (0A)
DH On-time is triggered when
V
FB
reaches the FB Threshold.
(500mV)
On-time (T
ON
)
DL drives high when on-time is completed.
DL remains high until inductor current reaches zero.
Dead time varies
according to load
Figure 6 Power-Save Operation
Smart Power-Save Protection
Active loads may leak current from a higher voltage into
the switcher output. Under light load conditions with
power-save enabled, this can force V
OUT
to slowly rise and
reach the over-voltage threshold, resulting in a hard shut-
down. Smart power-save prevents this condition. When
the FB voltage exceeds 0% above nominal (exceeds
550mV), the device immediately disables power-save and
DL drives high to turn on the low-side MOSFET. This draws
current from V
OUT
through the inductor and causes V
OUT
to
fall. When V
FB
drops back to the 500mV trip point, a normal
T
ON
switching cycle begins. This method prevents a hard
OVP shutdown and cycles energy from V
OUT
back to V
IN
. It
also minimizes operating power by avoiding forced con-
duction mode operation. Figure 7 shows typical wave-
forms for the Smart Power-save feature.
Applications Information (continued)
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