参数资料
| 型号： | SC174MLTRT |
| 厂商： | Semtech |
| 文件页数： | 11/27页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 4A 10MLPD |
| 产品培训模块： | Power Supplies 101 |
| 标准包装： | 1 |
| 系列： | EcoSpeed® |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.75 V ~ 5.23 V |
| 输入电压： | 3 V ~ 5.5 V |
| 频率 - 开关： | 200kHz ~ 1MHz |
| 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： | 10-VFDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 10-MLPD（3x3） |
| 其它名称： | SC174MLDKR |
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SC174
The adaptive on-time is determined by an internal one-
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Applications Information
SC174 Synchronous Buck Converter
The SC174 is a step down synchronous buck dc-dc regu-
lator. The SC174 is capable of 4A operation at very high
efficiency in a tiny 3x3-10 pin package. The programma-
ble operating frequency range of 200kHz – 1MHz enables
the user to optimize the solution for minimum board
space and optimum efficiency.
The buck regulator employs pseudo-fixed frequency
adaptive on-time control. This control scheme allows
fast transient response thereby lowering the size of the
power components used in the system.
Input Voltage Range
The SC174 can operate with an input voltage ranging
from 3V to 5.5V.
Psuedo-fixed Frequency Adaptive On-time Control
The PWM control method used by the SC174 is pseudo-
fixed frequency, adaptive on-time, as shown in Figure 1.
The ripple voltage generated at the output capacitor ESR
is used as a PWM ramp signal. This ripple is used to trig-
ger the on-time of the controller.
shot timer. When the one-shot is triggered by the out-
put ripple, the device sends a single on-time pulse to the
high-side MOSFET. The pulse period is determined by
V OUT and V IN ; the period is proportional to output voltage
and inversely proportional to input voltage. With this
adaptive on-time arrangement, the device automatically
anticipates the on-time needed to regulate V OUT for the
present V IN condition and at the selected frequency.
The advantages of adaptive on-time control are:
? Predictable operating frequency compared to
other variable frequency methods.
Reduced component count by eliminating
the error amplifier and compensation compo-
nents.
Reduced component count by removing the
need to sense and control inductor current.
Fast transient response — the response time
is controlled by a fast comparator instead of a
typically slow error amplifier.
Reduced output capacitance due to fast tran-
sient response
One-Shot Timer and Operating Frequency
The one-shot timer operates as shown in Figure 2. The
FB Comparator output goes high when V FB is less than
the internal 750mV reference. This feeds into the gate
drive and turns on the high-side MOSFET, and also starts
Q1
Q2
V IN
V LX
C IN
L
ESR
T ON
V FB
V LX
FB threshold
V OUT
the one-shot timer. The one-shot timer uses an internal
comparator, timing capacitor, and a low pass filter (LPF)
which regenerates V OUT from LX. One comparator input
is connected to the filtered LX voltage, the other input is
connected to the capacitor. When the on-time begins,
the internal capacitor charges from zero volts through a
current which is proportional to V IN . When the capacitor
voltage reaches V OUT , the on-time is completed and the
high-side MOSFET turns off.
C OUT
+
FB
This method automatically produces an on-time that is
proportional to V OUT and inversely proportional to V IN .
Under steady-state operation conditions, the switching
frequency can be determined from the on-time by the
following equation.
Figure 1 — PWM Control Method, V OUT Ripple
? 2010 Semtech Corporation
f SW =
V OUT
T ON × V IN
11
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