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| 型号： | MAX8744ETJ+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 26/36页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP QUAD 32TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 60 |
| 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： | 管件 |
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High-Efficiency, Quad-Output, Main Power-
Supply Controllers for Notebook Computers
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
accordingly. Extremes of low input-output differentials,
widely different output loading levels, and high turns
ratios can further complicate the design due to parasitic
L =
V OUT ( V IN ? V OUT )
V IN f OSC I LOAD ( MAX ) LIR
transformer parameters such as interwinding capaci-
tance, secondary resistance, and leakage inductance.
Power from the main and secondary outputs is com-
bined to get an equivalent current referred to the main
For example: I LOAD(MAX) = 5A, V IN = 12V, V OUT = 5V,
f OSC = 300kHz, 30% ripple current or LIR = 0.3:
output. Use this total current to determine the current
limit (see the Setting the Current Limit section):
L =
5 V x ( 12 V ? 5 V )
12 V x 300 kHz x 5 A x 0 . 3
= 6 . 50 μ H
I TOTAL = P TOTAL /V OUT5
where I TOTAL is the equivalent output current referred
to the main output, and P TOTAL is the sum of the output
power from both the main output and the secondary
Find a low-loss inductor having the lowest possible DC
output:
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
nonstandard values, which can provide a better compro-
N =
V SEC + V FWD
V OUT 5 + V RECT + V SENSE
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:
where N is the transformer turns ratio, V SEC is the mini-
mum required rectified secondary voltage, V FWD is the
forward drop across the secondary rectifier,
V OUT5(MIN) is the minimum value of the main output
voltage, and V RECT is the on-state voltage drop across
the synchronous-rectifier MOSFET. The transformer
Δ I INDUCTOR = OUT IN OUT
V ( V ? V
V IN f OSC L
)
secondary return is often connected to the main output
voltage instead of ground in order to reduce the neces-
sary turns ratio. In this case, subtract V OUT5 from the
secondary voltage (V SEC - V OUT5 ) in the transformer
Ferrite cores are often the best choice, although pow-
dered iron is inexpensive and can work well at 200kHz.
The core must be large enough not to saturate at the
peak inductor current (I PEAK ):
turns-ratio equation above. The secondary diode in
coupled-inductor applications must withstand flyback
voltages greater than 60V. Common silicon rectifiers,
such as the 1N4001, are also prohibited because they
I PEAK = I LOAD ( MAX ) +
Δ I INDUCTOR
2
are too slow. Fast silicon rectifiers such as the MURS120
are the only choice. The flyback voltage across the recti-
fier is related to the V IN - V OUT5 difference, according to
the transformer turns ratio:
Transformer Design (for
MAX8744/MAX8745 Auxiliary Output)
A coupled inductor or transformer can be substituted
for the inductor in the 5V SMPS to create an auxiliary
output (Figure 1). The MAX8744/MAX8745 is particular-
ly well suited for such applications because the sec-
ondary feedback threshold automatically triggers DL5
even if the 5V output is lightly loaded.
The power requirements of the auxiliary supply must be
considered in the design of the main output. The trans-
former must be designed to deliver the required current
in both the primary and the secondary outputs with the
proper turns ratio and inductance. The power ratings of
the synchronous-rectifier MOSFETs and the current limit
in the MAX8744/MAX8745 must also be adjusted
V FLYBACK = V SEC + (V IN – V OUT5 ) x N
where N is the transformer turns ratio (secondary wind-
ings/primary windings), and V SEC is the maximum sec-
ondary DC output voltage. If the secondary winding is
returned to V OUT5 instead of ground, subtract V OUT5
from V FLYBACK in the equation above. The diode ’s
reverse breakdown voltage rating must also accommo-
date any ringing due to leakage inductance. The
diode’s current rating should be at least twice the DC
load current on the secondary output.
Transient Response
The inductor ripple current also impacts transient-
response performance, especially at low V IN - V OUT dif-
ferentials. Low inductor values allow the inductor
26
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| MAX8745ETJ+ | 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 |
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