参数资料
| 型号： | SC2446ITETRT |
| 厂商： | Semtech |
| 文件页数： | 21/38页 |
| 文件大小： | 0K |
| 描述： | IC SYNC STEP DOWN CTRLR 28-TSSOP |
| 标准包装： | 1 |
| 应用： | 控制器，DDR |
| 输入电压： | 4.7 V ~ 16 V |
| 输出数： | 2 |
| 输出电压： | 可调至 0.5V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 供应商设备封装： | 28-TSSOP 裸露焊盘 |
| 包装： | 标准包装 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC2446ITEDKR |
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SC2446
POWER MANAGEMENT
Application Information (Cont.)
off until it is no longer overloaded. This hiccup mode of
R s C s =
L
R eq
,
overload protection is a form of foldback current limiting.
The following calculations estimate the average inductor
current when the converter output is shorted to the
for R s and R S3 .
I LM R eq +
R s
R s 3
V O = 75 mV ,
ground.
a) The time taken to discharge the capacitor from 3.2V
to 0.5V
R s2 is then obtained from
t ssf = C 32
( 3 .2 ? 0 .5 ) V
1 . 4 μ A
.
R s 2 =
R s 3 R s
R s 3 ? R s
.
If C 32 = 0.1 μ F, t ssf is calculated as 193ms.
b) The soft start time from 0.5V to 3.2V
t ssr = C 32
( 3 . 2 ? 0 . 5 ) V
If the current limit is to be set to I LM = 5A with the existing
power circuit parameter and C s , it is calculated that
R s =4.12 k ? , R s3 =190 k ? and R s2 =4.22 k ? .
Similar steps and equations apply to the current limit
setting and scaling for current sinking mode.
Remark 4 : When the current limit I LM is lower than I LMcp ,
the designer has the freedom of selecting higher Rds(ON)
.
2 μ A
When C 32 = 0.1 μ F, t ssr is calculated as 135ms. Note that
during soft start, the converter only starts switching when
the voltage at SS/EN exceeds 1.2V.
c) The effective start-up time is
MOSFETs to reduce cost. As a result, R eg is increased
and I LMcp is reduced. Although the use of low-cost
MOSFET’s is always preferred, the current-limit setting
t sso = C 32
( 3 .2 ? 1. 2 ) V
2 μ A
.
technique described above allows quick adjustment on a
well-tested prototype without the need to replace the
The average inductor current is then
power MOSFETs.
Overload Protection and Hiccup
I Leff = I LMcp
t sso
t ssf + t ssr
.
R o 2 =
R o 1 .
During start-up, the capacitor from the SS/EN pin to
ground functions as a soft-start capacitor. After the
converter starts and enters regulation, the same
capacitor operates as an overload shutoff timing
capacitor. As the load current increases, the cycle-by-
cycle current-limit comparator will first limit the inductor
current. Further increase in loading will cause the output
voltage (hence the feedback voltage) to fall. If the
feedback voltage falls to less than (75% for Ch1, 72%
for Ch2) of the reference voltage, the controller will shut
off both the top and the bottom MOSFET’s. Meanwhile
an internal 1. 4μ A current source discharges the soft-start
capacitor C 32 (C 33 ) connected to the SS/EN pin.
When the capacitor is discharged to 0.5V, a 2 μ A current
source recharges the SS/EN capacitor and converter
restarts. If overload persists, the controller will shut down
the converter when the soft start capacitor voltage
exceeds 3.2V. The converter will repeatedly start and shut
I Leff ≈ 0.30 I LMcp and is independent of the soft start
capacitor value. The converter will not overheat in hiccup.
Setting the Output Voltage
The non-inverting input of the channel-one error amplifier
is internally tied the 0.5V voltage reference output (Pin
8). The non-inverting input of the channel-two error
amplifier is brought out as a device pin (Pin 10) to which
the user can connect Pin 8 or an external voltage
reference. A simple voltage divider (R o1 at top and R o2 at
bottom) sets the converter output voltage. The voltage
feedback gain h=0.5/V o is related to the divider resistors
value as
h
1 ? h
? 2004 Semtech Corp.
21
www.semtech.com
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| SC2446ITSTRT | 制造商:Semtech Corporation 功能描述:Controller IC 制造商:Semtech Corporation 功能描述:SC Series 4.7 to 16 V 1 MHz Dual-Phase Synchronous Step-Down Controller TSSOP-28 |
| SC2447 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
| SC24-470-R | 功能描述:INDUCTOR SHIELD 47UH 150MA SMD RoHS:是 类别:电感器，线圈，扼流圈 >> 固定式 系列:SC24 标准包装:500 系列:1331 电感:1.2µH 电流:247mA 电流 - 饱和:247mA 电流 - 温升:- 类型:铁芯体 容差:±10% 屏蔽:屏蔽 DC 电阻(DCR):最大 730 毫欧 Q因子@频率:40 @ 7.9MHz 频率 - 自谐振:130MHz 材料 - 芯体:铁 封装/外壳:0.312" L x 0.115" W x 0.135" H（7.94mm x 2.92mm x 3.43mm） 安装类型:表面贴装 包装:带卷 (TR) 工作温度:-55°C ~ 105°C 频率 - 测试:7.9MHz |
| SC24-471-R | 功能描述:INDUCTOR SHIELD 470UH 50MA SMD RoHS:是 类别:电感器，线圈，扼流圈 >> 固定式 系列:SC24 标准包装:500 系列:1331 电感:1.2µH 电流:247mA 电流 - 饱和:247mA 电流 - 温升:- 类型:铁芯体 容差:±10% 屏蔽:屏蔽 DC 电阻(DCR):最大 730 毫欧 Q因子@频率:40 @ 7.9MHz 频率 - 自谐振:130MHz 材料 - 芯体:铁 封装/外壳:0.312" L x 0.115" W x 0.135" H（7.94mm x 2.92mm x 3.43mm） 安装类型:表面贴装 包装:带卷 (TR) 工作温度:-55°C ~ 105°C 频率 - 测试:7.9MHz |
| SC2447EVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
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