参数资料
| 型号： | SC174MLTRT |
| 厂商： | Semtech |
| 文件页数： | 12/27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
Applications Information (continued)
Enable and Power-save Inputs
The EN/PSV input is used to enable or disable the switch-
FB
REF
V OUT
V IN
PWM
-
+
On-Shot Timing
Generator
S
R
Q
Hi-Side
and
Lo-Side
Gate
Drivers
V IN
Q1
V LX
Q2
LPF
L
ESR
C OUT
+
V OUT
FB
ing regulator. When EN/PSV is low (grounded), the switch-
ing regulator is off and in its lowest power state. When
off, the output power switches are tri-stated. When EN/
PSV is allowed to float, the pin voltage will float to 41%
of the voltage at V DD . The switching regulator turns on
with power-save disabled and all switching is in forced
R TON
Time = K x V OUT /V IN
continuous mode.
R TON
1
Figure2—On-TimeGeneration
The SC174 uses an external resistor to set the on-time
which indirectly sets the frequency. The on-time can
be programmed to provide operating frequency from
200kHz to 1MHz using a resistor between the TON pin
and ground. The resistor value is selected by the fol-
lowing equation.
=
25pF ? f SW
V OUT Voltage Selection
The switcher output voltage is regulated by comparing
V OUT as seen through a resistor divider at the FB pin to
the internal 750mV reference voltage, see Figure 3.
When EN/PSV is high (above 60% of the voltage at V DD ),
the switching regulator turns on with ultrasonic power-
save enabled. The SC174 ultrasonic power-save opera-
tion maintains a minimum switching frequency of 25kHz,
for applications with stringent audio requirements.
Forced Continuous Mode Operation
The SC174 operates in Forced Continuous Mode (FCM)
by floating the EN/PSV pin (see Figure 4). In this mode
one of the power MOSFETs is always on, with no inten-
tional dead time other than to avoid cross-conduction.
This feature results in uniform frequency across the full
load range with the trade-off being poor efficiency at
light loads due to the high-frequency switching of the
MOSFETs.
V OUT
R 1
To FB pin
FB Ripple
Voltage (V FB )
FB threshold
(750mV)
R 2
Figure 3 — Output Voltage Selection
Inductor
Current
DC Load Current
Note that this control method regulates the valley of the
output ripple voltage, not the DC value. The DC output
voltage V OUT is offset by the output ripple according to
the following equation.
DH
On-time
(T ON )
DH on-time is triggered when
V FB reaches the FB Threshold.
V OUT = 0.75V ? ? ? 1 +
R 1 ? V
R 2 ? ?
DL drives high when on-time is completed.
DL remains high until V FB falls to the FB threshold.
?2010SemtechCorporation
?
?
? + RIPPLE
2
DL
Figure 4 — Forced Continuous Mode Operation
12
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