参数资料
| 型号： | SC4518HSETRT |
| 厂商： | Semtech |
| 文件页数： | 10/15页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 2A 8-SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出数： | 1 |
| 输入电压： | 4.4 V ~ 24 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 600kHz |
| 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-SO 裸露焊盘 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC4518HSEDKR |
SC4518H
POWER MANAGEMENT
Application Information (Cont.)
V BOOST = input voltage or output based on the boost circuit
Where:
I O = load current;
R = on-equivalent resistance of the switch;
ON
connection.
The junction temperature of the SC4518H can be
The goal of the compensation design is to shape the loop
to have a high DC gain, high bandwidth, enough phase
margin, and high attenuation for high frequency noises.
Figure 3 gives a typical compensation network which
offers 2 poles and 1 zero to the power stage:
further decided by:
2
IN
SC4518 H
3
SW
L1
Vout
T J = T A + θ JA ? P total
5
EN
FB
6
R1
C
θ JA is the thermal resistance from junction to ambient.
Its value is a function of the IC package, the application
layout and the air cooling system.
8
SYNC
COMP
7
C5
C4
R3
D2
R2
The freewheeling diode also contributes a significant
portion of the total converter loss. This loss should be
minimized to increase the converter efficiency by using
Schottky diodes with low forward drop (V F ).
P diode = V F ? I o ? ( 1 ? D )
Figure 3. Compensation network provides 2 poles and 1
zero.
The compensation network gives the following
characteristics:
1 +
s ? ( 1 +
Loop Compensation Design
The SC4518H has an internal error amplifier and requires
a compensation network to connect between the COMP
pin and GND pin as shown in Figure 3. The compensation
G COMP ( s ) = ω 1 ?
s
ω Z
s
ω P 2
)
? g m ?
R 2
R 1 + R 2
network includes C4, C5 and R3. R1 and R2 are used to
program the output voltage according to:
Where:
V O = 0 . 8 ? ( 1 +
R 1
R 2
)
ω 1 =
1
C 4 + C 5
Assuming the power stage ESR (equivalent series
resistance) zero is an order of magnitude higher than
the closed loop bandwidth, which is typically one tenth of
the switching frequency, the power stage control to output
ω Z =
1
R 3 ? C 4
transfer function with the current loop closed (Ridley
model) for the SC4518H will be as follows:
ω P 2 =
C 4 + C 5
R 3 ? C 4 ? C 5
1 +
1 +
? 3 R L R 2 1 ω Z
C 4 R 1 + R 2 s ( 1 + s ) ? ( 1 + s )
G VD ( s ) =
Where:
R L – Load and
C – Output capacitor.
? 2007 Semtech Corp.
3 ? R L
s
1
R L ? C
10
The loop gain will be given by:
T ( s ) = G COMP ( s ) ? G VD ( s ) = 2 . 55 ? 10 ? ? ?
s
ω P 1 ω P 2
www.semtech.com
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