参数资料
| 型号： | SC121ULTRT |
| 厂商： | Semtech |
| 文件页数： | 18/23页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST SYNC 3.3V/ADJ 6MLPD |
| 标准包装： | 1 |
| 类型： | 升压（升压） |
| 输出类型： | 两者兼有 |
| 输出数： | 1 |
| 输出电压： | 3.3V，1.8 V ~ 5 V |
| 输入电压： | 0.7 V ~ 4.5 V |
| 频率 - 开关： | 1.2MHz |
| 电流 - 输出： | 500mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 6-MLPD-UT |
| 包装： | 标准包装 |
| 供应商设备封装： | 6-MLPD-UT（1.5x2.0） |
| 其它名称： | SC121ULTRTDKR |
SC121
Applications Information (continued)
duty cycle must remain between 20% and 90% for the
device to operate within specification.
Note that startup with a regulated active load is not the
same as startup with a resistive load. The resistive load
output current increases proportionately as the output
voltage rises until it reaches programmed V OUT /R LOAD , while
a regulated active load presents a constant load as the
output voltage rises from 0V to programmed V OUT . Note
also that if the load applied to the output exceeds an
applicable V OUT –dependent startup current limit or duty
cycle limit, the criterion to advance to the next startup
stage may not be achieved. In this situation startup may
pause at a reduced output voltage until the load is reduced
further.
Output Overload and Recovery
The PWM steady state duty cycle is determined by
D = 1 – (V IN /V OUT ), but must be somewhat greater in prac-
tice to overcome dissipative losses. As the output load
increases, the dissipative losses also increase. The PWM
controller must increase the duty cycle to compensate.
Eventually, one of two overload conditions will occur,
determined by V IN , V OUT , and the overall dissipative losses
due to the output load current. Either the maximum duty
cycle of 90% will be reached or the n-channel FET 1.2A
(nominal) peak current limit will be reached, which effec-
tively limits the duty cycle to a lower value. Above that
load, the output voltage will decrease rapidly and in
Once an overload has occurred, the load must be
decreased to permit recovery. The conditions required for
overload recovery are identical to those required for suc-
cessful initial startup.
Component Selection
The SC121 provides optimum performance when a 4.7μH
inductor is used with a 10μF output capacitor. Different
component values can be used to modify input current or
output voltage ripple, improve transient response, or to
reduce component size or cost.
Inductor Selection
The inductance value primarily affects the amplitude of
inductor peak-to-peak current ripple ( Δ I L ). Reducing
inductance increases Δ I L and raises the inductor peak
current, I L-max = I L-avg + Δ I L /2, where I L-avg is the inductor
current averaged over a full on/off cycle. I L-max is subject to
the n-channel FET current limit I LIM(N) , therefore reducing
the inductance may lower the output overload current
threshold. Increasing Δ I L also lowers the inductor
minimum current, I L-min = I L-avg – Δ I L /2, thus raising the load
current threshold below which inductor negative –peak
current becomes zero.
Equating input power to output power and noting that
input current is equal to inductor current, average the
inductor current over a full PWM switching cycle to
obtain
reverse order the startup current limits will be invoked as
the output voltage falls through its various voltage thresh-
olds. How far the output voltage drops depends on the
I L
avg
1 V OUT I OUT
V IN
load voltage vs. current characteristic.
where η is effi ciency.
A reduction in input voltage, such as a discharging battery,
will lower the load current at which overload occurs.
Lower input voltage increases the duty cycle required to
Neglecting the n-channel FET R DS-ON and the inductor DCR,
for duty cycle D, and with T = 1/f osc ,
produce a given output voltage. And lower input voltage
also increases the input current to maintain the input
power, which increases dissipative losses and further
I L
on
1
L
DT
0
V IN dt
V IN D T
L
increases the required duty cycle. Therefore an increase in
load current or a decrease in input voltage can result in
output overload. Please refer to the Max. I OUT vs. V IN Typical
Characteristics plots for the condition that best matches
This is the change in I L during the on-state. During the
off-state, again neglecting the p-channel FET R DS-ON and
the inductor DCR,
the application.
I L
off
1
L
T
DT
V IN V OUT dt
V IN V OUT
L
T
1 D
18
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相关代理商/技术参数 |
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| SC122 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Low Voltage Synchronous Boost Converter |
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| SC122EVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Low Voltage Synchronous Boost Converter |
| SC122ULTRT | 功能描述:IC REG BST SYNC 3.3V 95MA 6MLPD RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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