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| 型号： | MAX8744AETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 32/36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
The output capacitor and the load resistance create the
dominant pole in the system. However, the internal ampli-
5) Next, calculate the zero caused by the output
capacitor’s ESR:
fier delay, the pass transistor’s input capacitance, and the
stray capacitance at the feedback node create additional
poles in the system, and the output capacitor’s ESR gen-
f ZERO ( ESR ) =
1
2 π C OUTA R ESR
erates a zero. For proper operation, use the following
steps to ensure the linear-regulator stability:
1) First, calculate the dominant pole set by the linear
regulator’s output capacitor and the load resistor:
where R ESR is the equivalent series resistance of
C OUTA .
6) To ensure stability, choose C OUTA large enough so
that the crossover occurs well before the poles and
f POLE ( LDO ) =
1
2 π C OUTA R LOAD
zero calculated in steps 2 through 5. The poles in
steps 3 and 4 generally occur at several MHz, and
using ceramic output capacitors ensures the ESR
zero occurs at several MHz as well. Placing the
f POLE ( CIN ) ≈
C IN =
f POLE ( CIN ) ≈ T
where C OUTA is the output capacitance of the aux-
iliary LDO and R LOAD is the load resistance corre-
sponding to the maximum load current. The unity-
gain crossover of the linear regulator is:
f CROSSOVER = A V(LDO) f POLE(LDO)
2) The pole caused by the internal amplifier delay is at
approximately 1MHz:
f POLE(AMP) ≈ 1MHz
3) Next, calculate the pole set by the transistor’s input
capacitance, the transistor’s input resistance, and
the base-to-emitter pullup resistor. Since the tran-
sistor’s input resistance (h FE /g m ) is typically much
greater than the base-to-emitter pullup resistance,
the pole can be determined from the simplified
equation:
1
2 π C IN R IN
g m
2 π f T
where g m is the transconductance of the pass tran-
sistor, and f T is the transition frequency. Both para-
meters can be found in the transistor’s data sheet.
Therefore, the equation can be further reduced to:
f
h FE
4) Next, calculate the pole set by the linear regulator’s
feedback resistance and the capacitance between
FBA and ground (approximately 5pF including
stray capacitance):
crossover frequency below 500kHz is typically suf-
ficient to avoid the amplifier delay pole and gener-
ally works well, unless unusual component
selection or extra capacitance moves the other
poles or zero below 1MHz.
A capacitor connected between the linear regula-
tor’s output and the feedback node can improve
the transient response and reduce the noise cou-
pled into the feedback loop.
If a low-dropout solution is required, an external
p-channel MOSFET pass transistor could be used.
However, a pMOS-based linear regulator requires
higher output capacitance to stabilize the loop. The
high gate capacitance of the p-channel MOSFET
lowers the f POLE(CIN) and can cause instability. A
large output capacitance must be used to reduce
the unity-gain bandwidth and ensure that the pole
is well above the unity-gain crossover frequency.
Applications Information
Duty-Cycle Limits
Minimum Input Voltage
The minimum input operating voltage (dropout voltage) is
restricted by the maximum duty-cycle specification (see
the Electrical Characteristics table). However, keep in
mind that the transient performance gets worse as the
step-down regulators approach the dropout voltage, so
bulk output capacitance must be added (see the voltage
sag and soar equations in the Transient Response sec-
tion of the SMPS Design Procedure section). The
absolute point of dropout occurs when the inductor cur-
rent ramps down during the off-time ( Δ I DOWN ) as much
as it ramps up during the on-time ( Δ I UP ). This results in a
minimum operating voltage defined by the following
f POLE ( FBA ) =
1
2 π C FBA ( R 5 || R 6 )
equation:
32
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相关代理商/技术参数 |
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|---|---|
| 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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