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參數(shù)資料
| 型號： | SC427MLTRT |
| 廠商： | Semtech |
| 文件頁數(shù)： | 21/33頁 |
| 文件大?。?/td> | 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
21
Power Good Output
The power good (PGOOD) output is an open-drain output
which requires a pull-up resistor. When the output voltage
is 10% below the nominal voltage, PGOOD is pulled low. It
is held low until the output voltage returns above -8% of
nominal. PGOOD is held low during start-up and will not
be allowed to transition high until soft-start is completed
(when V
FB
reaches 500mV) and typically 2ms has passed.
PGOOD will transition low if the V
FB
pin exceeds +20% of
nominal, which is also the over-voltage shutdown thresh-
old (600mV). PGOOD also pulls low if the EN/PSV pin is
low when V5V is present.
Output Over-Voltage Protection
Over-voltage protection becomes active as soon as the
device is enabled. The threshold is set at 500mV + 20%
(600mV). When V
FB
exceeds the OVP threshold, DL latches
high and the low-side MOSFET is turned on. DL remains
high and the controller remains off, until the EN/PSV input
is toggled or V5V is cycled. There is a 5約 delay built into
the OVP detector to prevent false transitions. PGOOD is
also low after an OVP event.
Output Under-Voltage Protection
When V
FB
falls 25% below its nominal voltage (falls to
375mV) for eight consecutive clock cycles, the switcher is
shut off and the DH and DL drives are pulled low to tri-
state the MOSFETs. The controller stays off until EN/PSV is
toggled or V5V is cycled.
V5V UVLO, and POR
Under-Voltage Lock-Out (UVLO) circuitry inhibits switching
and tri-states the DH/DL drivers until V5V rises above 3.9V.
An internal Power-On Reset (POR) occurs when V5V exceeds
3.9V, which resets the fault latch and soft-start counter to
prepare for soft-start. The SC417/SC427 then begins a soft-
start cycle. The PWM will shut off if V5V falls below 3.6V.
LDO Regulator
The LDO output is programmable from 0.75V to 5.25V
using external resistors. The feedback pin (FBL) for the
LDO is regulated to 750mV. There is also an enable pin
(ENL) for the LDO that provides independent control. The
LDO voltage can also be used to provide the bias voltage
for the switching regulator. When a separate source is
used as the bias supply, the LDO can be programmed to
provide a different voltage (see Figure 9).
VLDO
To FBL pin
R
LDO2
R
LDO1
Figure 9 LDO Start-Up
The LDO output voltage is set by the following equation.
2
LDO
1
LDO
R
R
1
mV
750
VLDO
A minimum capacitance of 1糉 referenced to AGND is
normally required at the output of the LDO for stability. If
the LDO is providing bias power to the device, then a
minimum 0.1糉 capacitor referenced to AGND is required
along with a minimum 1.0糉 capacitor referenced to
PGND to filter the gate drive pulses. Refer to the layout
guidelines section.
LDO ENL Functions
The ENL input is used to enable/disable the internal LDO.
When ENL is a logic low, the LDO is off. When ENL is a high
but below the VIN UVLO threshold (2.6V typical), then the
LDO is on and the switcher is off. When ENL is above the V
IN
UVLO threshold, the LDO is enabled and the switcher is also
enabled if the EN/PSV pin is not grounded. The table below
summarizes the function of ENL and EN/PSV pins.
EN/PSV
ENL
LDO Switcher
Disabled Low, < 0.4V OFF OFF
Enabled Low, < 0.4V OFF ON
Disabled 1.0V < High < 2.6V ON OFF
Enabled 1.0V < High < 2.6V ON OFF
Disabled High, > 2.6V ON OFF
Enabled High, > 2.6V ON ON
The ENL pin also acts as the switcher under-voltage lockout
for the V
IN
supply. When SC417/SC427 is self-biased from
the LDO and runs from the V
IN
power source only, the VIN
UVLO feature can be used to prevent false UV faults for the
PWM output by programming with a resistor divider at the
VIN, ENL and AGND pins. When SC417/SC427 has an exter-
Applications Information (continued)
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