参数资料
| 型号： | SC2440TETRT |
| 厂商： | Semtech |
| 文件页数： | 10/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 2A DL 16TSSOP |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出数： | 2 |
| 输入电压： | 2.8 V ~ 20 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： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-TSSOP |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC2440TEDKR |
SC2440
POWER MANAGEMENT
Applications Information
Minimum On Time Consideration
D 2 =
3 . 3 + 0 . 45
13 . 2 + 0 . 45 ? 0 . 25
= 0 . 28
The operating duty cycle of a step-down switching
regulator with diode rectifier in continuous-conduction
mode (CCM) is given by
130
Minimum On Time vs Temperature
D =
V OUT + V D
V IN + V D ? V CESAT
(2)
120
110
V IN
V OUT
V OUT
V IN
T ON(MIN) . If the required switch on time (= ) is shorter
D 1
D 2
D 1 =
= 0 . 11
V OUT
V IN
where V CESAT is the switch saturation voltage and V D is
voltage drop across the rectifying diode.
Duty cycle decreases with increasing ratio. In peak
current-mode control, the PWM modulating ramp is the
sensed current ramp of the power switch. This current
ramp is absent unless the switch is turned on. The
intersection of this ramp with the output of the voltage
feedback error amplifier determines the switch pulse
width. The propagation delay time required to
immediately turn off the switch after it is turned on is
the minimum switch on time (T ON (MIN) ). Closed-loop
measurement of the SC2440 with low ratios shows
that the minimum on time is about 105ns at room
temperature. T ON (MIN) also exhibits a slight positive
temperature coefficient (Figure 6). The power switch in
the SC2440 is either not turned on at all or for at least
D
f
than the minimum on time, the regulator will either skip
cycles or it will jitter.
Example: Determine the maximum operating frequency
of a dual 12V to 1.0V and 12V to 3.3V switching
regulator using the SC2440.
Assuming that V D = 0.45V, V CESAT = 0.25V and V IN = 13.2V
(10% high line), the corresponding duty ratios, D 1 and
D 2 , of the 1.0V and 3.3V converters can be calculated
using (2).
1 + 0 . 45
13 . 2 + 0 . 45 ? 0 . 25
100
90
80
-40 -20 0 20 40 60 80 100
Temperature (°C)
Figure 6. Variation of Minimum On Time with
Temperature.
If the ambient temperature can be as high as 85 ° C, then
the maximum operating frequencies of the 1.0V and the
3.3V converters will be = 920 KHz and
120 ns
= 2 . 3 MHz respectively..
120 ns
Channel frequency should be set below 920KHz to allow
margin for load transient.
Minimum Off Time Limitation
The PWM latch in Figure 2 is reset every period 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
switching frequency. Measurement shows that the power
transistor needs to be turned off for at least 120ns every
switching period to properly reset the latch and to refresh
the bootstrap capacitor. For a step-down converter, D
increases with increasing ratio. If the required duty
cycle is higher than the attainable maximum, then the
? 2005 Semtech Corp.
10
www.semtech.com
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相关代理商/技术参数 |
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| SC2441 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441A | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441A_09 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441AEVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ATETRT | 制造商:Semtech Corporation 功能描述: |
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