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| 型号： | SC403MLTRT |
| 厂商： | Semtech |
| 文件页数： | 15/32页 |
| 文件大小： | 741K |
| 描述： | IC REG DL BCK/LINEAR SYNC 32MLPQ |
| 标准包装： | 1 |
| 系列： | EcoSpeed®, SmartDrive™ |
| 拓扑： | 降压（降压）同步（1），线性（LDO）（1） |
| 功能： | 任何功能 |
| 输出数： | 2 |
| 频率 - 开关： | 1MHz |
| 电压/电流 - 输出 1： | 可调至 0.75V，6A |
| 电压/电流 - 输出 2： | 可调至 0.75V，200mA |
| 带 LED 驱动器： | 无 |
| 带监控器： | 无 |
| 带序列发生器： | 是 |
| 电源电压： | 3 V ~ 28 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-VFQFN 裸露焊盘 |
| 供应商设备封装： | 32-MLPQ（5x5） |
| 包装： | 标准包装 |
| 其它名称： | SC403MLDKR |
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SC403
15
Synchronous Buck Converter
The SC403 is a step down synchronous DC-DC buck con-
verter with integrated power MOSFETs and a 200mA pro-
grammable LDO. The device operates at a current up to
6A at very high efficiency. A space saving 5x5 (mm) 32-pin
package is used. The programmable operating frequency
of up to 1MHz enables optimizing the configuration for
PCB area and efficiency.
The buck controller uses a pseudo-fixed frequency adap-
tive on-time control. This control method allows fast tran-
sient response which permits the use of smaller output
capacitors.
Input Voltage Requirements
The SC403 requires two input supplies for normal opera-
tion: V
IN
and V
DD
. V
IN
operates over a wide range from 3V to
28V. VDD requires a supply voltage between 3V to 5V that
can be an external source or the internal LDO from V
IN
.
Power Up Sequence
The SC403 initiates a start up when VIN, VDD, and EN/PSV
pins are above the applicable thresholds. When using an
external bias supply for the V
DD
voltage, it is recommended
that the V
DD
is applied to the device only after the V
IN
voltage is present because V
DD
cannot exceed V
IN
at any
time. A 10& resistor must be placed between the external
V
DD
supply and the VDD pin to avoid damage to the device
during power-up and or shutdown situations where V
DD
could exceed V
IN
unexpectedly.
Shutdown
The SC403 can be shutdown by pulling either VDD or EN/
PSV pin below its threshold. When using an external
supply voltage for V
DD
, the VDD pin must be deactivated
while the V
IN
voltage is still present. A 10& resistor must
be placed between the external V
DD
supply and the VDD
pin to avoid damage to the device.
When the VDD pin is active and EN/PSV is at low logic
level, the output voltage discharges through an internal
FET.
Psuedo-fixed Frequency Adaptive On-time Control
The PWM control method used by the SC403 is pseudo-
fxed 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 trigger
the controller on-time.
Q1
Q2
L
C
OUT
ESR
+
C
IN
V
OUT
FB Threshold
V
FB
V
LX
V
LX
TON
FB
V
IN
Figure 1 PWM Control Method, V
OUT
Ripple
The adaptive on-time is determined by an internal one-
shot timer. When the one-shot is triggered by the output
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 antici-
pates 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 components.
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 typi-
cally slow error amplifier.
Reduced output capacitance due to fast tran-
sient response
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Applications Information
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