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参数资料
| 型号： | MAX8744AETJ+T |
| 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 |
| 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
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 ):
60V. Common silicon rectifiers, such as the 1N4001, are
also prohibited because they are too slow. Fast silicon
rectifiers such as the MURS120 are the only choice. The
flyback voltage across the rectifier is related to the V IN -
I PEAK = I LOAD ( MAX ) +
Δ I INDUCTOR
2
V OUT5 difference, according to the transformer turns
ratio:
V FLYBACK = V SEC + (V IN – V OUT5 ) x N
Transformer Design (for
MAX8744A/MAX8745A 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 MAX8744A/MAX8745A is partic-
ularly well suited for such applications because the
secondary 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 MAX8744A/MAX8745A must also be adjusted
accordingly. Extremes of low input-output differentials,
widely different output loading levels, and high turns
ratios can further complicate the design due to parasitic
transformer parameters such as interwinding capaci-
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
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The total output voltage sag is the sum of the voltage
sag while the inductor is ramping up, and the voltage
sag before the next pulse can occur:
(
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
output. Use this total current to determine the current
limit (see the Setting the Current Limit section):
V SAG =
L ( Δ I LOAD ( MAX ) ) 2
2 C OUT V IN xD MAX ? V OUT
Δ I LOAD ( MAX ) ( T ? Δ T )
)
+
V SEC + V FWD
V OUT 5 + V RECT SENSE
+ V
≈ ( Δ I LOAD ( MAX ) ) 2 L
I LIMIT > I LOAD ( MAX ) + ? ? Δ I INDUCTOR ? ?
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
output:
N =
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 synchro-
nous-rectifier MOSFET. The transformer secondary return
is often connected to the main output voltage instead of
ground in order to reduce the necessary turns ratio. In
this case, subtract V OUT5 from the secondary voltage
(V SEC - V OUT5 ) in the transformer turns-ratio equation
above. The secondary diode in coupled-inductor appli-
cations must withstand flyback voltages greater than
C OUT
where D MAX is maximum duty factor (see the Electrical
Characteristics), T is the switching period (1/f OSC ), and
Δ T equals V OUT /V IN x T when in PWM mode, or L x 0.2 x
I MAX /(V IN - V OUT ) when in skip mode. The amount of
overshoot during a full-load to no-load transient due to
stored inductor energy can be calculated as:
V SOAR
2 C OUT V OUT
Setting the Current Limit
The minimum current-limit threshold must be great
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The
peak inductor current occurs at I LOAD(MAX) plus half
the ripple current; therefore:
? 2 ?
26
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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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