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| 型号： | MAX1977EEI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 27/32页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PS QUAD HI EFF 28QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4.5 V ~ 24 V |
| 输出数： | 4 |
| 输出电压： | 3.3V，5V，2 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-QSOP |
| 供应商设备封装： | 28-QSOP |
| 包装： | 管件 |
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High-Efficiency, Quad Output, Main Power-
Supply Controllers for Notebook Computers
( )
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
(>5A) when using high-voltage (>20V) AC adapters.
Low-current applications usually require less attention.
Choose a high-side MOSFET (N1/N3) that has conduc-
tion losses equal to the switching losses at the typical
battery voltage for maximum efficiency. Ensure that the
conduction losses at the minimum input voltage do not
exceed the package thermal limits or violate the overall
thermal budget. Ensure that conduction losses plus
switching losses at the maximum input voltage do not
exceed the package ratings or violate the overall ther-
mal budget.
Choose a synchronous rectifier (N2/N4) with the lowest
possible R DS(ON) . Ensure the gate is not pulled up by the
high-side switch turning on due to parasitic drain-to-gate
tance, and PC board layout characteristics. The follow-
ing switching loss calculation provides only a very
rough estimate and is no substitute for bench evalua-
tion, preferably including verification using a thermo-
couple mounted on N1/N3:
PD N 1 / N 3 switching =
? 2 ?
? C RSS × V + ( MAX ) × f × I LOAD ?
? ?
? I GATE ?
? ?
where C RSS is the reverse transfer capacitance of
N1/N3 and I GATE is the peak gate-drive source/sink
current.
For the synchronous rectifier, the worst-case power dis-
sipation always occurs at maximum battery voltage:
PD ( N 2 / N 4 ) = ? 1 ?
V + ( MAX ) ?
capacitance, causing cross-conduction problems.
Switching losses are not an issue for the synchronous
rectifier in the buck topology, since it is a zero-voltage
switched device when using the buck topology.
?
?
V OUT _ ? 2
? × I LOAD × R DS
? V OUT _ ?
? V + ( MIN ) ?
MOSFET Power Dissipation
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET, the worst-case
power dissipation (PD) due to the MOSFET’s R DS(ON)
occurs at minimum battery voltage:
PD ( N 1 / N 3 resis tan ce ) = ? ?×
I LOAD 2 × R DS ( ON )
Generally, a small high-side MOSFET reduces switch-
ing losses at high input voltage. However, the R DS(ON)
required to stay within package power-dissipation limits
often limits how small the MOSFET can be. The opti-
mum situation occurs when the switching (AC) losses
equal the conduction (R DS(ON) ) losses.
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum battery volt-
age is applied, due to the squared term in the CV 2 ? f
switching loss equation. Reconsider the high-side
MOSFET chosen for adequate R DS(ON) at low battery
voltages if it becomes extraordinarily hot when subject-
ed to V+ (MAX) .
Calculating the power dissipation in N1/N3 due to
switching losses is difficult since it must allow for quan-
tifying factors that influence the turn-on and turn-off
times. These factors include the internal gate resis-
tance, gate charge, threshold voltage, source induc-
The absolute worst case for MOSFET power dissipation
occurs under heavy overloads that are greater than
I LOAD(MAX) but are not quite high enough to exceed
the current limit and cause the fault latch to trip. To
protect against this possibility, “overdesign” the circuit
to tolerate:
I LOAD = I LIMIT(HIGH) + (LIR / 2 ) x I LOAD(MAX)
where I LIMIT(HIGH) is the maximum valley current
allowed by the current-limit circuit, including threshold
tolerance and resistance variation.
Rectifier Selection
Current circulates from ground to the junction of both
MOSFETs and the inductor when the high-side switch is
off. As a consequence, the polarity of the switching
node is negative with respect to ground. This voltage is
approximately -0.7V (a diode drop) at both transition
edges while both switches are off (dead time). The drop
is I L x R DS(ON) when the low-side switch conducts.
The rectifier is a clamp across the synchronous rectifier
that catches the negative inductor swing during the dead
time between turning the high-side MOSFET off and the
synchronous rectifier on. The MOSFETs incorporate a
high-speed silicon body diode as an adequate clamp
diode if efficiency is not of primary importance. Place a
Schottky diode in parallel with the body diode to reduce
the forward voltage drop and prevent the N2/N4 MOSFET
body diodes from turning on during the dead time.
Typically, the external diode improves the efficiency by
1% to 2%. Use a Schottky diode with a DC current rating
equal to one-third of the load current. For example, use
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1977EEI+ | 功能描述:DC/DC 开关控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1977EEI+T | 功能描述:DC/DC 开关控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1977EEI-T | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1977EEI-TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1978ETM | 功能描述:电压模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
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