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參數(shù)資料
| 型號： | SC424MLTRT |
| 廠商： | Semtech |
| 文件頁數(shù)： | 17/29頁 |
| 文件大?。?/td> | 496K |
| 描述： | IC REG DL BUCK/LINEAR 28MLPQ |
| 標(biāo)準(zhǔn)包裝： | 1 |
| 系列： | SmartDrive™ |
| 拓?fù)洌?/td> | 降壓（降壓）（1），線性（LDO）（1） |
| 功能： | 任何功能 |
| 輸出數(shù)： | 2 |
| 頻率 - 開關(guān)： | 200kHz ~ 1MHz |
| 電壓/電流 - 輸出 1： | 可調(diào)至 0.75V，6A |
| 電壓/電流 - 輸出 2： | 5V，150mA |
| 帶 LED 驅(qū)動(dòng)器： | 無 |
| 帶監(jiān)控器： | 無 |
| 帶序列發(fā)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： | 28-VFQFN 裸露焊盤 |
| 供應(yīng)商設(shè)備封裝： | 28-MLPQ（4x4） |
| 包裝： | 標(biāo)準(zhǔn)包裝 |
| 其它名稱： | SC424MLDKR |
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SC414/SC424
17
Because the on-times are forced to occur at intervals no
greater than 40約, the frequency will not fall far below
25kHz. Figure 5 shows ultrasonic power-save operation.
FB Ripple
Voltage (V
FB
)
FB threshold
(750mV)
Inductor
Current
DH
DL
(0A)
40約 time-out
minimum f
SW
~ 25kHz
After the 40約ec 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
)
Figure 5 Ultrasonic Power-save Operation
Power-save Mode Operation (SC424)
The SC424 provides power-save operation at light loads
with no minimum operating frequency. With power-save
enabled, the internal zero crossing comparator monitors
the inductor current via the voltage across the low-side
MOSFET during the off -time. If the inductor current falls to
zero for 8 consecutive switching cycles, the controller
enters power-save operation. It will turn off the low-side
MOSFET on each subsequent cycle provided that the
current crosses zero. At this time both MOSFETs remain
off until V
FB
drops to the 750mV threshold. Because the
MOSFETs are off , the load is supplied by the output capaci-
tor. If the inductor current does not reach zero on any
switching cycle, the controller immediately 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.
(750mV)
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 10% above nominal (exceeds
825mV), 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 750mV trip point, a normal
T
ON
switching cycle begins. This method prevents a hard
OVP shutdown and also cycles energy from V
OUT
back to
V
IN
. It also minimizes operating power by avoiding forced
conduction mode operation. Figure 7 shows typical wave-
forms for the Smart Power-save feature.
SmartDrive
TM
For each DH pulse, the DH driver initially turns on the
high-side MOSFET at a slower speed, allowing a softer,
smooth turn-off of the low-side diode. Once the DH node
is high and the LX voltage has risen 1V above PGND, the
SmartDrive circuit automatically drives the high-side
MOSFET on at a rapid rate. This technique reduces ringing
while maintaining high efficiency and also avoids the
need for snubbers or series resistors in the gate drive.
Applications Information (continued)
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