参数资料
| 型号： | MAX8741EAI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 25/34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： | 46 |
| 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： | 管件 |
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500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
Table 5. Low-Voltage Troubleshooting Chart
SYMPTOM
Sag or droop in V OUT
under step-load change
Dropout voltage is too
high (V OUT follows V IN as
V IN decreases)
Unstable—jitters between
different duty factors and
frequencies
Secondary output does
not support a load
Poor efficiency
Does not start under load
or quits before battery is
completely dead
CONDITION
Low V IN - V OUT
differential, <1.5V
Low V IN - V OUT
differential, <1V
Low V IN - V OUT
differential, <0.5V
Low V IN - V OUT
differential,
V IN < 1.3 x
V OUT(MAIN)
Low input voltage,
<5V
Low input voltage,
<4.5V
ROOT CAUSE
Limited inductor-current slew rate
per cycle.
Maximum duty-cycle limits
exceeded.
Normal function of internal low-
dropout circuitry.
Not enough duty cycle left to
initiate forward-mode operation.
Small AC current in primary
cannot store energy for flyback
operation.
V L linear regulator is going into
dropout and is not providing
good gate-drive levels.
V L output is so low that it hits the
V L UVLO threshold.
SOLUTION
Increase bulk output capacitance per
formula (see the Low-Voltage Operation
section). Reduce inductor value.
Reduce operation to 333kHz. Reduce
MOSFET on-resistance and coil DCR.
Increase the minimum input voltage or
ignore.
Reduce operation to 333kHz. Reduce
secondary impedances; use a Schottky
diode, if possible. Stack secondary
winding on the main output.
Use a small 20mA Schottky diode for
boost diode. Supply V L from an external
source.
Supply V L from an external source other
than V IN , such as the system 5V supply.
improved by connecting V L to an efficient 5V source,
such as the system 5V supply:
P(diode) = I LOAD ? V FWD ? t D ? f
where t D is the diode-conduction time (120ns typ) and
V FWD is the forward voltage of the diode.
This power is dissipated in the MOSFET body diode if
no external Schottky diode is used:
cy, use MOSFETs with moderate gate-charge levels, and
use ferrite, MPP, or other low-loss core material.
Lossless-Inductor Current Sensing
The DC resistance (DCR) of the inductor can be used
to sense inductor current to improve the efficiency and
to reduce the cost by eliminating the sense resistor.
Figure 7 shows the sense circuit, where L is the induc-
tance, R L is the inductor DCR, and R S and C S form an
RC lowpass sense network. If the time constant of the
inductor is equal to that of the sense network, i.e.,:
P(cap) = (I RMS ) 2 x R ESR
L
R L
= R S C S
where I RMS is the input ripple current as calculated in the
Design Procedure and Input-Capacitor Value sections.
Light-Load Efficiency Considerations
Under light loads, the PWM operates in discontinuous
mode, where the inductor current discharges to zero at
some point during the switching cycle. This makes the
inductor current’s AC component high compared to the
load current, which increases core losses and I 2 R losses
in the output filter capacitors. For best light-load efficien-
then the voltage across C S becomes:
V S = R L × I L
where I L is the inductor current.
Determine the required sense-resistor value using the
equation given in the Current-Sense Resistor Value
section. Choose an inductor with DCR equal to or
greater than the sense resistor value. If the DCR is
greater than the sense-resistor value, use a divider to
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8741EAI+ | 功能描述:电流和电力监控器、调节器 500kHz Multi-Out Pwr Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8741EAI+T | 功能描述:电流和电力监控器、调节器 500kHz Multi-Out Pwr Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8741EAI-T | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8742EAI | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8742EAI+ | 功能描述:电流和电力监控器、调节器 500kHz Multi-Out Pwr Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
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