参数资料
| 型号： | SC4517AIMSTRT |
| 厂商： | Semtech |
| 文件页数： | 10/15页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.5A 8MSOP |
| 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： | 可调 |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.25MHz |
| 电流 - 输出： | 1.5A |
| 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） |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-MSOP |
| 其它名称： | SC4517AIMSDKR |
SC4517A
POWER MANAGEMENT
Application Information (Cont.)
1 +
Thermal Considerations
There are three major power dissipation sources for the
SC4517A. The internal switch conduction loss, its
switching loss due to the high frequency switching actions
G VD ( s ) =
2 . 5 ? R L
s
1
R L ? C
P total = I o ? R on ? D + 22 . 5 ? 10 ? 3 ? I o ? V I +
? I o ? D ? ( V boost )
V BOOST = input voltage or output based on the boost circuit
and the base drive boost circuit loss. These losses can
be estimated as:
2 10
500
Where:
I O = load current;
R = on-equivalent resistance of the switch;
ON
connection.
The junction temperature of the SC4517A can be
further decided by:
T J = T A + θ JA ? P total
Where:
R L – Load and
C – Output capacitor.
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:
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. It is recommended that
a big copper area attached to Pin 4 or the thermal pad
be used for better cooling condition.
2
5
8
IN
EN
SYNC
SC4517
SW
FB
COMP
3
6
7
C5
C4
L1
R1
R2
C
Vout
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
R3
D2
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 SC4517A 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
Where:
V O = 1 . 2 ? ( 1 +
R 1
program the output voltage according to:
)
R 2
Assuming the power stage ESR (equivalent series
resistance) zero is an order of magnitude higher than
ω 1 =
ω Z =
1
C 4 + C 5
1
R 3 ? C 4
the closed loop bandwidth, which is typically one tenth of
the switching frequency, the power stage control to output
transfer function with the current loop closed (Ridley
model) for the SC4517A will be as follows:
? 2006 Semtech Corp.
10
ω P 2 =
C 4 + C 5
R 3 ? C 4 ? C 5
www.semtech.com
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相关代理商/技术参数 |
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| SC4517AIMSXXTRT | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:1.25MHz, 1.5A Step-Down Switching Regulator |
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