参数资料
| 型号： | SC4524SETRT |
| 厂商： | Semtech |
| 文件页数： | 11/21页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 2A 8SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出数： | 1 |
| 输入电压： | 2.8 V ~ 30 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.4MHz |
| 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-SOIC（0.154"，3.90mm 宽） |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-SOIC-EP |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC4524SEDKR |
SC4524
POWER MANAGEMENT
Applications Information
duty-cycle invariant and are guaranteed higher than 2.3A.
The maximum load current is therefore conservatively
10 m F X5R ceramic capacitor is adequate. For high voltage
applications, a small ceramic (1 m F or 2.2 m F) can be
placed in parallel with a low ESR electrolytic capacitor to
satisfy both the ESR and bulk capacitance requirements.
,
= ,
-
D ,
= $ -
D ,
(5)
Output Capacitor
,
= ,
-
= D , ì ì (65 +
ü ü
D 9
I&
í
Y
If D , = ? , , then
D ,
= ,
-
,
= ? , .
The output ripple voltage D V OUT of a buck converter can
be expressed as
? ?
(7)
( at ' =
Equation (6) has a maximum value of ),
in C IN .
The saturation current of the inductor should be 20-30%
higher than the peak current limit (2.3A). Low-cost
powder iron cores are not suitable for high-frequency
switching power supplies due to their high core losses.
Inductors with ferrite cores should be used.
Power Line Input Capacitor
A buck converter draws pulse current with peak-to-peak
amplitude equal to its output current I OUT from its input
supply. An input capacitor placed between the supply
and the buck converter filters the AC current and keeps
the current drawn from the supply to a DC constant. The
input capacitance C IN should be high enough to filter the
pulse input current. Its equivalent series resistance (ESR)
should be low so that power dissipated in the capacitor
does not result in significant temperature rise and
degrade reliability. For a buck converter, the RMS ripple
current in the input capacitor is
, = , ' - ' . (6)
Power dissipated in the input capacitor is , ? (65 .
,
corresponding to the worst-case power dissipation
, ? (65
Multi-layer ceramic capacitors, which have very low ESR
(a few m W ) and can easily handle high RMS ripple current,
are the ideal choice for input filtering. A single 4.7 m F or
where C OUT is the output capacitance.
Inductor ripple current D I L increases as D decreases
(Equation (3)). The output ripple voltage is therefore the
highest when V IN is at its maximum. The first term in (7)
results from the ESR of the output capacitor while the
second term is due to the charging and discharging of
C OUT by the inductor ripple current. Substituting D I L =
0.69A, f = 500kHz and C OUT = 22 m F ceramic with ESR =
2m W in (7),
D 9 = $ ? P W + P W
= P9 + P9 = P9
Depending on operating frequency and the type of
capacitor, ripple voltage resulting from charging and
discharging of C OUT may be higer than that due to ESR. A
10 m F to 47 m F X5R ceramic capacitor is found adequate
for output filtering in most applications. Ripple current
in the output capacitor is not a concern because the
inductor current of a buck converter directly feeds C OUT ,
resulting in very low ripple current. Avoid using Z5U and
Y5V ceramic capacitors for output filtering because these
types of capacitors have high temperature and high
voltage coefficients.
Freewheeling Diode
Use of Schottky barrier diodes as freewheeling rectifiers
reduces diode reverse recovery input current spikes,
easing high-side current sensing in the SC4524. These
diodes should have an average forward current rating
between 1A and 2A and a reverse blocking voltage of at
least a few volts higher than the input voltage. For
switching regulators operating at low duty cycles (i.e. low
? 2006 Semtech Corp.
11
www.semtech.com
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