参数资料
| 型号： | SC410MLTRT |
| 厂商： | Semtech |
| 文件页数： | 15/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 3A 10MLPD |
| 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 ~ 7.5 V |
| 输入电压： | 5.5 V ~ 24 V |
| 频率 - 开关： | 200kHz ~ 1MHz |
| 电流 - 输出： | 3A |
| 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： | SC410MLDKR |
SC410
Applications Information (continued)
V OUT drifts up to due to leakage
current flowing into C OUT
Smart Power Save
Threshold (825mV)
FB
threshold
DH and DL off
High-side
Drive (DH)
Single DH on-time pulse
after DL turn-off
Low-side
Drive (DL)
DL turns on when Smart
PSAVE threshold is reached
V OUT discharges via inductor
and low-side MOSFET
Normal V OUT ripple
Normal DL pulse after
DH on-time pulse
In the SC410, the valley current limit is set to 3A. This results
in a peak inductor current of 3A plus the peak-to-peak
ripple current. In this situation, the average (load) current
through the inductor is 3A plus one-half the peak-to-peak
ripple current.
The internal 10μA current source is temperature compen-
sated at 2500ppm in order to provide tracking with the
RDS ON .
Peak Inductor Current
The peak current through the inductor and switching FETs
must be less than 5A. The only way to meet this require-
DL turns off when FB
threshold is reached
Figure 6 — Smart Power Save
Current Limit Protection
The current limiting is accomplished by using the RDS ON of
the lower MOSFET for current sensing. The current limit is
set by an internal resistor R ILIM . The resistor connects from
an ILIM node to the LX node which is also the drain of the
low-side MOSFET. When the low-side MOSFET is on, an
internal ~10μA current flows from the ILIM Node and
through the R ILIM resistor, creating a voltage drop across the
resistor. While the low-side MOSFET is on, the inductor
current flows through it and creates a voltage across the
RDS ON . The voltage across the MOSFET is negative with
respect to ground. If this MOSFET voltage drop exceeds the
voltage across R ILIM , the voltage at the ILIM node will be
negative and current limit will activate. The current limit
then keeps the low-side MOSFET on and will not allow
another high-side on-time, until the current in the low-side
MOSFET reduces enough to bring the ILIM voltage back up
to zero. This method regulates the inductor valley current
at the level shown by ILIM in Figure 7.
I PEAK
I LOAD
I LIM
Time
ment is to select the switching frequency and inductor
value such that the peak inductor current is less than or
equal to 5A when the trough of the inductor current is
3A.
Soft start of PWM Regulator
Soft start is achieved in the PWM regulator by using an
internal voltage ramp as the reference for the FB com-
parator. The voltage ramp is generated using an internal
charge pump which drives the reference from zero to
750mV in ~1.8mV increments, using an internal ~500kHz
oscillator. When the ramp voltage reaches 750mV, the
ramp is ignored and the FB comparator switches over to
a fixed 750mV threshold. During soft start the output
voltage tracks the internal ramp, which limits the start-up
inrush current and provides a controlled soft start profile
for a wide range of applications. Typical soft start ramp
time is 850μs.
During soft start the regulator turns off the low-side
MOSFET on any cycle if the inductor current falls to zero.
This prevents negative inductor current, allowing the
device to start into a pre-biased output.
Power Good Output
The PGOOD (power good) 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 to the nominal
voltage. PGOOD is held low during soft start and activated
approximately 1ms after V OUT reaches regulation.
Figure 7 — Valley Current Limit
15
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