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| 型号： | SC185QULTRT |
| 厂商： | Semtech |
| 文件页数： | 15/18页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 3.3V 4A 16MLPQ |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 2.9 V ~ 5.5 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 1.5MHz |
| 电流 - 输出： | 4A |
| 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： | 16-UFQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-MLPQ-UT（3x3） |
| 其它名称： | SC185QULDKR |
SC185
Applications Information (continued)
in circuit whenever the EN pin is below its threshold, or
when the device is in under voltage lockout and AVIN
exceeds 0.8V. When the device is enabled, it takes about
50μs for the internal circuitry wake up and begin the soft-
start up sequence.
Operation Mode Selection
The MODE input is used to select between forced PWM
and automatic PSAVE modes. When the MODE pin is held
high, the device operates in forced continuous PWM mode
regardless of the output load condition. When the MODE
pin is held low (grounded), the device is permitted to
operate in Power Save mode (PSAVE). The MODE pin can
be changed on-the-fly. When the MODE pin is switched
from low to high, the device will transition to forced
continuous PWM mode immediately. When the MODE
pin is switched from high to low, and the load current is
below the PSAVE entry level, the device will transition to
PSAVE mode after 64 clock cycles. The MODE pin has a
500kΩ internal pull-down resistor. This resistor is switched
in circuit whenever the MODE pin is below its threshold,
or when the device is in under voltage lockout but AVIN
exceeds 0.8V.
100% Duty-Cycle Operation
SC185 is capable of operating at 100% duty-cycle. When
the difference between input voltage to output voltage
is less than the minimum dropout voltage, the PMOS
switch is completely on, operating in 100% duty-cycle.
The minimum dropout voltage is the output current
multiplied by the on-resistance of the internal PMOS
switch and the DC-resistance of the inductor when PMOS
switch is on continuously.
Output L-C filter Selection
SC185 has fixed internal loop-gain compensation. It is
optimized for X5R or X7R ceramic output capacitors and
an output L-C filter corner frequency of less than 34KHz.
The output L-C corner frequency can be determined by
Equation 2.
value of 1μH to 2.2μH with output ceramic capacitors of
44μF or higher capacitance. Lower inductance should
be considered in applications where faster transient
response is required. More output capacitance will reduce
the output deviation for a particular load transient. When
using low inductance, the maximum peak inductor
current at any condition (normal operation and start up)
can not exceed 5A which is the guaranteed minimum
current limit. The saturation current rating of the inductor
needs to be at least larger than the peak inductor current
which is the maximum output current plus half of inductor
ripple current.
f C =
1
2 π L ? C OUT
(2)
In general, the inductor is chosen to set the inductor ripple
current to approximately 30% of the maximum output
current. It is recommended to use a typical inductor
? 2010 Semtech Corp.
15
www.semtech.com
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