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参数资料
| 型号： | SC4501MSETRT |
| 厂商： | Semtech |
| 文件页数： | 11/21页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST ADJ 2A 8MSOP |
| 标准包装： | 1 |
| 类型： | 升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 32V |
| 输入电压： | 1.4 V ~ 16 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.5MHz |
| 电流 - 输出： | 2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-MSOP-EP |
| 其它名称： | SC4501MSEDKR |
SC4501
POWER MANAGEMENT
Application Information
small sizes. However these types of capacitors have high
temperature and high voltage coefficients. For example,
the capacitance of a Z5U capacitor can drop below 60%
of its room temperature value at –25 ° C and 90 ° C. X5R
ceramic capacitors, which have stable temperature and
voltage coefficients, are the preferred type.
The diode current waveform in Figure 5 is discontinuous
with high ripple-content. In a buck converter the inductor
ripple current Δ I L determines the output ripple voltage.
The output ripple voltage of a boost regulator is however
much higher and is determined by the absolute inductor
current. Decreasing the inductor ripple current does not
appreciably reduce the output ripple voltage. The current
flowing in the output filter capacitor is the difference
between the diode current and the output current. This
capacitor current has a RMS value of:
forward voltages). This is because the diode conduction
interval is much longer than that of the transistor.
Converter efficiency will be improved if the voltage drop
across the diode is lower.
The rectifying diodes should be placed close to the SW
pins of the SC4501 to minimize ringing due to trace
inductance. Surface-mount equivalents of 1N5817,
1N5818, MBRM120 (ON Semi) and 10BQ015 (IRF) are
all suitable.
Soft-Start
Soft-start prevents a DC-DC converter from drawing
excessive current (equal to the switch current limit) from
the power source during start up. If the soft-start time is
made sufficiently long, then the output will enter regulation
without overshoot. An external capacitor from the SS pin
I OUT
V OUT
V IN
? 1
(8)
to the ground and an internal 1.5μA charging current
source set the soft-start time. The soft-start voltage ramp
at the SS pin clamps the error amplifier output. During
regulator start-up, COMP voltage follows the SS voltage.
If a tantalum capacitor is used, then its ripple current rating
in addition to its ESR will need to be considered.
When the switch is turned on, the output capacitor supplies
the load current I OUT (Figure 5). The output ripple voltage
due to charging and discharging of the output capacitor is
therefore:
The converter starts to switch when its COMP voltage
exceeds 0.7V. The peak inductor current is gradually
increased until the converter output comes into regulation.
If the shutdown pin is forced below 1.1V or if fault is
detected, then the soft-start capacitor will be discharged
to ground immediately.
The SS pin can be left open if soft-start is not required.
Δ V OUT =
I OUT DT
C OUT
(9)
Shutdown
The input voltage and shutdown pin voltage must be greater
For most applications, a 10-22μF ceramic capacitor is
sufficient for output filtering. It is worth noting that the
output ripple voltage due to discharging of a 10μF ceramic
capacitor (9) is higher than that due to its ESR.
Rectifying Diode
For high efficiency, Schottky barrier diodes should be used
as rectifying diodes for the SC4501. These diodes should
have a RMS current rating of at least 1A and a reverse
blocking voltage of at least a few Volts higher than the
output voltage. For switching regulators operating at low
duty cycles (i.e. low output voltage to input voltage
conversion ratios), it is beneficial to use rectifying diodes
with somewhat higher RMS current ratings (thus lower
than 1.4V and 1.1V respectively to enable the SC4501.
Forcing the shutdown pin below 1.1V stops switching.
Pulling this pin below 0.1V completely shuts off the SC4501.
The total V IN current decreases to 10μA at 2V. Figure 6
shows several ways of interfacing the control logic to the
shutdown pin. Beware that the shutdown pin is a high
impedance pin. It should always be driven from a low-
impedance source or tied to a resistive divider. Floating
the shutdown pin will result in undefined voltage. In Figure
6(c) the shutdown pin is driven from a logic gate whose
V OH is higher than the supply voltage of the SC4501. The
diode clamps the maximum shutdown pin voltage to one
diode voltage above the input power supply.
2011
? 2005 Semtech Corp.
11
www.semtech.com
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