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| 型号： | MAX8744AETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 25/36页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP QUAD 32TQFN |
| 标准包装： | 2,500 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 6 V ~ 26 V |
| 输出数： | 4 |
| 输出电压： | 3.3V，5V，1 V ~ 26 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 供应商设备封装： | 32-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
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High-Efficiency, Quad-Output, Main Power-
Supply Controllers for Notebook Computers
Auxiliary LDO Detailed Description
The MAX8744A/MAX8745A include an auxiliary linear
regulator (OUTA) that can be configured for 12V, ideal for
PCMCIA power requirements, and for biasing the gates
of load switches in a portable device. OUTA can also be
configured for outputs from 1V to 23V. The auxiliary regu-
lator has an independent ON/OFF control, allowing it to
be shut down when not needed, reducing power con-
sumption when the system is in a low-power state.
?
?
Switching Frequency. This choice determines the
basic trade-off between size and efficiency. The opti-
mal frequency is largely a function of maximum input
voltage, due to MOSFET switching losses that are
proportional to frequency and V IN 2 . The optimum fre-
quency is also a moving target, due to rapid improve-
ments in MOSFET technology that are making higher
frequencies more practical.
Inductor Operating Point. This choice provides
V OUT ( V IN ? V OUT )
5 V x ( 12 V ? 5 V )
A flyback-winding control loop regulates a secondary
winding output, improving cross-regulation when the pri-
mary output is lightly loaded or when there is a low input-
output differential voltage. If V DRVA < V OUTA , the
low-side switch is turned on for a time equal to 33% of
the switching period. This reverses the inductor (primary)
current, pulling current from the output filter capacitor
and causing the flyback transformer to operate in for-
ward mode. The low impedance presented by the trans-
former secondary in forward mode dumps current into
the secondary output, charging up the secondary
capacitor and bringing V INA - V OUTA back into regula-
tion. The secondary feedback loop does not improve
secondary output accuracy in normal flyback mode,
where the main (primary) output is heavily loaded. In this
condition, secondary output accuracy is determined by
the secondary rectifier drop, transformer turns ratio, and
accuracy of the main output voltage.
SMPS Design Procedure
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point, and the fol-
lowing four factors dictate the rest of the design:
? Input Voltage Range. The maximum value
(V IN(MAX) ) must accommodate the worst-case, high
AC-adapter voltage. The minimum value (V IN(MIN) )
must account for the lowest battery voltage after
drops due to connectors, fuses, and battery selector
switches. If there is a choice at all, lower input volt-
ages result in better efficiency.
? Maximum Load Current. There are two values to
consider. The peak load current (I LOAD(MAX) )
determines the instantaneous component stresses
and filtering requirements and thus drives output
capacitor selection, inductor saturation rating, and
the design of the current-limit circuit. The continu-
trade-offs between size vs. efficiency and transient
response vs. output ripple. Low inductor values pro-
vide better transient response and smaller physical
size, but also result in lower efficiency and higher out-
put ripple due to increased ripple currents. The mini-
mum practical inductor value is one that causes the
circuit to operate at the edge of critical conduction
(where the inductor current just touches zero with
every cycle at maximum load). Inductor values lower
than this grant no further size-reduction benefit. The
optimum operating point is usually found between
20% and 50% ripple current. When pulse skipping
( SKIP low and light loads), the inductor value also
determines the load-current value at which
PFM/PWM switchover occurs.
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
L =
V IN f OSC I LOAD ( MAX ) LIR
For example: I LOAD(MAX) = 5A, V IN = 12V, V OUT = 5V,
f OSC = 300kHz, 30% ripple current or LIR = 0.3:
L = = 6 . 50 μ H
12 V x 300 kHz x 5 A x 0 . 3
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Most induc-
tor manufacturers provide inductors in standard values,
such as 1.0μH, 1.5μH, 2.2μH, 3.3μH, etc. Also look for
non-standard values, which can provide a better compro-
mise in LIR across the input voltage range. If using a
swinging inductor (where the no-load inductance
decreases linearly with increasing current), evaluate the
LIR with properly scaled inductance values. For the
selected inductance value, the actual peak-to-peak
inductor ripple current ( Δ I INDUCTOR ) is defined by:
Δ I INDUCTOR = OUT IN OUT
ous load current (I LOAD ) determines the thermal
stresses and thus drives the selection of input
capacitors, MOSFETs, and other critical heat-con-
tributing components.
V ( V ? V
V IN f OSC L
)
______________________________________________________________________________________
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8744AEVKIT+ | 制造商:Maxim Integrated Products 功能描述:MAX8744A EVAL KIT - Rail/Tube |
| MAX8744ETJ+ | 功能描述:电流型 PWM 控制器 Quad-Out Main Power Supply 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 |
| MAX8744ETJ+T | 功能描述:电流和电力监控器、调节器 Quad-Out Main Power 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 |
| MAX8744EVKIT | 制造商:Maxim Integrated Products 功能描述:HIGH-EFFICIENCY QUAD OUTPUT MAIN - Rail/Tube |
| MAX8744EVKIT+ | 制造商:Maxim Integrated Products 功能描述:HIGH-EFFICIENCY QUAD OUTPUT MAIN - Rail/Tube |
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