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| 型号： | MAX8742EAI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 21/34页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP 28-SSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,000 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4.2 V ~ 30 V |
| 输出数： | 2 |
| 输出电压： | 3.3V，5V，2.5 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SSOP（0.209"，5.30mm 宽） |
| 供应商设备封装： | 28-SSOP |
| 包装： | 带卷 (TR) |
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500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
Inductor Value
The exact inductor value is not critical and can be
freely adjusted to make trade-offs between size, cost,
and efficiency. Lower inductor values minimize size
and cost but reduce efficiency due to higher peak-cur-
rent levels. The smallest inductor is achieved by lower-
ing the inductance until the circuit operates at the
border between continuous and discontinuous mode.
Further reducing the inductor value below this
crossover point results in discontinuous-conduction
operation even at full load. This helps lower output-filter
capacitance requirements, but efficiency suffers due to
high I 2 R losses. On the other hand, higher inductor val-
ues mean greater efficiency, but resistive losses due to
The inductor’s DC resistance should be low enough that
R DC ? I PEAK < 100mV, as it is a key parameter for effi-
ciency performance. If a standard off-the-shelf inductor is
not available, choose a core with an LI 2 rating greater
than L ? I PEAK 2 and wind it with the largest diameter wire
that fits the winding area. Ferrite core material is strongly
preferred. Shielded-core geometries help keep noise,
EMI, and switching-waveform jitter low.
Current-Sense Resistor Value
The current-sense resistor value is calculated accord-
ing to the worst-case low current-limit threshold voltage
(from the Electrical Characteristics ) and the peak
inductor current:
extra wire turns eventually exceed the benefit gained
from lower peak-current levels. Also, high inductor val-
ues can affect load-transient response (see the V SAG
R SENSE =
80mV
I PEAK
equation in the Low-Voltage Operation section). The
equations that follow are for continuous-conduction
operation, since the MAX8741/MAX8742 are intended
mainly for high-efficiency, battery-powered applica-
tions. Discontinuous conduction does not affect normal
idle-mode operation.
Three key inductor parameters must be specified: induc-
Use I PEAK from the second equation in the Inductor
Value section.
Use the calculated value of R SENSE to size the MOSFET
switches and specify inductor saturation-current ratings
according to the worst-case high current-limit threshold
voltage:
tance value (L), peak current (I PEAK ), and DC resistance
(R DC ). The following equation includes a constant (LIR),
which is the ratio of inductor peak-to-peak AC current to
DC load current. A higher LIR value allows smaller
I PEAK ( MAX ) =
120 mV
R SENSE
inductance but results in higher losses and higher ripple.
A good compromise between size and losses is found at
a 30% ripple-current to load-current ratio (LIR = 0.3),
which corresponds to a peak-inductor current 1.15 times
higher than the DC load current:
Low-inductance resistors, such as surface-mount
metal-film, are recommended.
Input-Capacitor Value
The input filter capacitor is usually selected according
V OUT ( IN ( MAX ) - V OUT )
L =
V
V IN ( MAX ) × f × I OUT × LIR
to input ripple-current requirements and voltage rating,
rather than capacitor value. Ceramic capacitors or
Sanyo OS-CON capacitors are typically used to handle
the power-up surge currents, especially when connect-
where:
f = switching frequency, normally 333kHz or 500kHz
I OUT = maximum DC load current
LIR = ratio of AC to DC inductor current, typically 0.3;
ing to robust AC adapters or low-impedance batteries.
RMS input ripple current (I RMS ) is determined by the
input voltage and load current, with the worst case
occurring at V IN = 2 ? V OUT :
should be >0.15
The nominal peak-inductor current at full load is 1.15 ?
I OUT if the above equation is used; otherwise, the peak
current can be calculated by:
I RMS = I LOAD ×
V OUT ( V IN - V OUT )
V IN
( V OUT IN ( MAX ) - V OUT ) )
I RMS = LOAD
I PEAK = I LOAD
+
( V
2 × f × L × V IN ( MAX )
Therefore, when V IN is 2 x V OUT :
I
2
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相关代理商/技术参数 |
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| MAX8743EEI | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX8743EEI+ | 功能描述:电流型 PWM 控制器 Dual Step-Down Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX8743EEI+T | 功能描述:电流型 PWM 控制器 Dual Step-Down Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX8743EEI-T | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX8743ETX | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
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