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参数资料
| 型号： | MAX8744AETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 30/36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
PD ( N H Re sistive ) = ? OUT ? ( I LOAD ) R DS ( ON )
The 40/60 optimal interleaved architecture of the
MAX8744A/MAX8745A allows the input voltage to go
as low 8.3V before the duty cycles begin to overlap.
This offers improved efficiency over a regular 180° out-
of-phase architecture where the duty cycles begin to
overlap below 10V. Figure 8 shows the input-capacitor
RMS current vs. input voltage for an application that
requires 5V/5A and 3.3V/5A. This shows the improve-
ment of the 40/60 optimal interleaving over 50/50 inter-
leaving and in-phase operation.
For most applications, nontantalum chemistries (ceramic,
aluminum, or OS-CON) are preferred due to their resis-
tance to power-up surge currents typical of systems
with a mechanical switch or connector in series with the
input. Choose a capacitor that has less than 10°C tem-
perature rise at the RMS input current for optimal relia-
bility and lifetime.
Power-MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
when using high-voltage (> 20V) AC adapters. Low-
current applications usually require less attention.
The high-side MOSFET (N H ) must be able to dissipate
? V ? 2
? V IN ?
Generally, use a small high-side MOSFET to reduce
switching losses at high input voltages. However, the
R DS(ON) required to stay within package power-dissipa-
tion limits often limits how small the MOSFET can be. The
optimum occurs when the switching losses equal the
conduction (R DS(ON) ) losses. High-side switching losses
do not become an issue until the input is greater than
approximately 15V.
Calculating the power dissipation in high-side MOSFETs
(N H ) due to switching losses is difficult, since it must
allow for difficult-to-quantify factors that influence the turn-
on and turn-off times. These factors include the internal
gate resistance, gate charge, threshold voltage, source
inductance, and PCB layout characteristics. The following
switching-loss calculation provides only a very rough esti-
mate and is no substitute for breadboard evaluation,
preferably including verification using a thermocouple
mounted on N H :
PD ( N H Switching ) =
?
?
? V IN ( MAX ) f SW
?
the resistive losses plus the switching losses at both
V IN(MIN) and V IN(MAX) . Ideally, the losses at V IN(MIN)
should be roughly equal to the losses at V IN(MAX) , with
? I LOAD Q G ( SW )
I GATE
+
C OSS V IN ( MAX ) ?
2
? ? ( I LOAD ) R DS ( ON )
? V IN ( MAX ) ? ? ?
? 1 ? ?
lower losses in between. If the losses at V IN(MIN) are
significantly higher, consider increasing the size of N H .
Conversely, if the losses at V IN(MAX) are significantly
higher, consider reducing the size of N H . If V IN does not
vary over a wide range, maximum efficiency is achieved
by selecting a high-side MOSFET (N H ) that has conduc-
tion losses equal to the switching losses.
Choose a low-side MOSFET (N L ) that has the lowest pos-
sible on-resistance (R DS(ON) ), comes in a moderate-sized
package (i.e., 8-pin SO, DPAK, or D 2 PAK), and is reason-
ably priced. Ensure that the MAX8744A/MAX8745A DL_
gate driver can supply sufficient current to support the
gate charge and the current injected into the parasitic
drain-to-gate capacitor caused by the high-side MOSFET
turning on; otherwise, cross-conduction problems may
occur. Switching losses are not an issue for the low-side
MOSFET since it is a zero-voltage switched device when
used in the step-down topology.
Power-MOSFET Dissipation
Worst-case conduction losses occur at the duty-factor
extremes. For the high-side MOSFET (N H ), the worst-
case power dissipation due to resistance occurs at mini-
mum input voltage:
where C OSS is the output capacitance of N H , Q G(SW) is
the charge needed to turn on the N H MOSFET, and I GATE
is the peak gate-drive source/sink current (1A typ).
Switching losses in the high-side MOSFET can become
a heat problem when maximum AC adapter voltages
are applied, due to the squared term in the switching-
loss equation (C x V IN 2 x f SW ). If the high-side MOSFET
chosen for adequate R DS(ON) at low battery voltages
becomes extraordinarily hot when subjected to
V IN(MAX) , consider choosing another MOSFET with
lower parasitic capacitance.
For the low-side MOSFET (N L ), the worst-case power
dissipation always occurs at maximum battery voltage:
PD ( N L Re sistive ) =
? ? V OUT ? ? 2
? ?
The absolute worst case for MOSFET power dissipation
occurs under heavy overload conditions that are
greater than I LOAD(MAX) , but are not high enough to
exceed the current limit and cause the fault latch to trip.
To protect against this possibility, “overdesign” the cir-
cuit to tolerate:
30
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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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