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參數(shù)資料
| 型號： | SC427MLTRT |
| 廠商： | Semtech |
| 文件頁數(shù)： | 20/33頁 |
| 文件大小： | 894K |
| 描述： | IC REG DL BUCK/LINEAR 32MLPQ |
| 標準包裝： | 1 |
| 系列： | EcoSpeed®, SmartDrive™ |
| 拓撲： | 降壓（降壓）（1），線性（LDO）（1） |
| 功能： | 任何功能 |
| 輸出數(shù)： | 2 |
| 頻率 - 開關： | 1MHz |
| 電壓/電流 - 輸出 1： | 可調(diào)，10A |
| 電壓/電流 - 輸出 2： | 5V，200mA |
| 帶 LED 驅(qū)動器： | 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： | 32-VFQFN 裸露焊盤 |
| 供應商設備封裝： | 32-MLPQ（5x5） |
| 包裝： | 標準包裝 |
| 其它名稱： | SC427MLDKR |
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SC417/SC427
20
FB
threshold
High-side
Drive (DH)
Low-side
Drive (DL)
V
OUT
drifts up to due to leakage
current flowing into C
OUT
DH and DL off
DL turns on when Smart
PSAVE threshold is reached
mart Power Save
hreshold (550mV)
DL turns off when FB
Single DH on-time pulse
after DL turn-off
V
OUT
discharges via inductor
and low-side MOSFET
Normal DL pulse after DH
on-time pulse
Normal V
OUT
ripple
Figure 7 Smart Power-save
Current Limit Protection
The device features programmable current limiting, which
is accomplished by using the RDS
ON
of the lower MOSFET
for current sensing. The current limit is set by R
ILIM
resistor.
The R
ILIM
resistor connects from the ILIM pin to the LX pin
which is also the drain of the low-side MOSFET. When the
low-side MOSFET is on, an internal ~10糀 current flows
from the ILIM pin and through the R
ILIM
resistor, creating a
voltage drop across the resistor. While the low-side MOSFET
is on, the inductor current flows through it and creates a
voltage across the RDS
ON
. The voltage across the MOSFET is
negative with respect to ground. If this MOSFET voltage
drop exceeds the voltage across R
ILIM
, the voltage at the ILIM
pin will be negative and current limit will activate. The
current limit then keeps the low-side MOSFET on and will
not allow another high-side on-time, until the current in the
low-side MOSFET reduces enough to bring the ILIM voltage
back up to zero. This method regulates the inductor valley
current at the level shown by ILIM in Figure 8.
Tim
I
PEAK
I
LOAD
I
LIM
Figure 8 Valley Current Limit
Setting the valley current limit to 10A results in a peak
inductor current of 10A plus peak ripple current. In this
situation, the average (load) current through the inductor
is 10A plus one-half the peak-to-peak ripple current.
The internal 10糀 current source is temperature compen-
sated at 4100ppm in order to provide tracking with the
RDS
ON
.
The R
ILIM
value is calculated by the following equation.
R
ILIM
= 735 x I
LIM
When selecting a value for R
ILIM
be sure not to exceed the
absolute maximum voltage value for the ILIM pin. Note
that because the low-side MOSFET with low RDS
ON
is used
for current sensing, the PCB layout, solder connections,
and PCB connection to the LX node must be done care-
fully to obtain good results. R
ILIM
should be connected
directly to LXS (pin 28).
Soft-Start of PWM Regulator
Soft-start is achieved in the PWM regulator by using an
internal voltage ramp as the reference for the FB
Comparator. The voltage ramp is generated using an
internal charge pump which drives the reference from
zero to 500mV in ~1.2mV increments, using an internal
~500kHz oscillator. When the ramp voltage reaches
500mV, the ramp is ignored and the FB comparator
switches over to a fixed 500mV threshold. During soft-start
the output voltage tracks the internal ramp, which limits
the start-up inrush current and provides a controlled soft-
start profile for a wide range of applications. Typical soft-
start ramp time is 850約.
Pre-Bias Startup
SC417/427 can start up into a pre-biased output voltage.
The start up time is approximately 850約 from enable to
regulation. The output voltage starts to ramp up when
the internal ramp meets the pre-charged FB voltage level.
Pre-bias startup is achieved by turning off the lower gate
when the inductor current falls below zero. This method
prevents output voltage discharge.
Applications Information (continued)
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相關代理商/技術參數(shù) |
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|---|---|
| SC428 | 制造商:Mallory 功能描述:Sonalert |
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| SC428312CFGE | 制造商:Freescale Semiconductor 功能描述: |
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