参数资料
| 型号： | SC4525CSETRT |
| 厂商： | Semtech |
| 文件页数： | 11/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A 8SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1 V ~ 26.88 V |
| 输入电压： | 3 V ~ 28 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 300kHz ~ 1.3MHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm Width）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-SOIC-EP |
| 其它名称： | SC4525CSEDKR |
SC4525C
Applications Information (Cont.)
To allow for transient headroom, the minimum operating
switch on time should be at least 20% to 30% higher than
the worst-case minimum on time.
200
An inductor ripple current between 20% to 50% of the
maximum load current, I O , gives a good compromise
among efficiency, cost and size. Re-arranging the previous
equation and assuming 35% inductor ripple current, the
inductor is given by
180
V O =1.5V, I O =1A, 1MHz
L =
( V O + V D ) x ( ? D )
35 % x I O x F SW
160
140
120
If the input voltage varies over a wide range, then choose
L based on the nominal input voltage. Always verify
converter operation at the input voltage extremes.
The peak current limit of SC4525C power transistor is at
least 3.9A. The maximum deliverable load current for the
SC4525C is 3.9A minus one half of the inductor ripple
current.
100
-50
-25
0 25 50 75
Temperature ( O C)
100 125
Input Decoupling Capacitor
The input capacitor should be chosen to handle the RMS
ripple current of a buck converter. This value is given by
Figure 4 — Variation of Minimum On Time
with Ambient Temperature
Minimum Off Time Limitation
The PWM latch in Figure 2 is reset every cycle by the
clock. The clock also turns off the power transistor to
refresh the bootstrap capacitor. This minimum off time
limits the attainable duty cycle of the regulator at a given
I RMS _ CIN = I O x D x ( ? D )
The input capacitance must also be high enough to keep
input ripple voltage within specification. This is important
in reducing the conductive EMI from the regulator. The
input capacitance can be estimated from
switching frequency. The measured minimum off time is
00ns typically. If the required duty cycle is higher than
the attainable maximum, then the output voltage will not
C IN >
I O
4 x D V IN x F SW
be able to reach its set value in continuous-conduction
mode.
Inductor Selection
The inductor ripple current for a non-synchronous step-
down converter in continuous-conduction mode is
where D V IN is the allowable input ripple voltage.
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 4.7μF
X5R ceramic capacitor is adequate for 500kHz or higher
D I L =
( V O + V D ) x ( ? D )
F SW x L
switching frequency applications, and 0μF is adequate
for 200kHz to 500kHz switching frequency. For high
voltage applications, a small ceramic ( μF or 2.2μF) can be
where F SW is the switching frequency and L is the
inductance.
placed in parallel with a low ESR electrolytic capacitor to
satisfy both the ESR and bulk capacitance requirements.
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