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| 型号： | MAX8744ETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 31/36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： | 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
? ? ( I LOAD ) R DS ( ON )
? V IN ( MAX ) ? ? ?
? 1 ? ?
PD ( N H Re sistive ) = ? OUT ? ( I LOAD DS ( ON )
) 2 R
I LOAD LIMIT ? ?
? Δ I INDUCTOR ?
?
?
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 MAX8744/MAX8745 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:
? V ?
? 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 ) =
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:
= I ?
2
where I LIMIT is the peak current allowed by the current-
limit circuit, including threshold tolerance and sense-
resistance variation. The MOSFETs must have a
relatively large heatsink to handle the overload power
dissipation.
Choose a Schottky diode (D L ) with a forward-voltage
drop low enough to prevent the low-side MOSFET’s
body diode from turning on during the dead time. As a
general rule, select a diode with a DC current rating
equal to a 1/3 the load current. This diode is optional
and can be removed if efficiency is not critical.
Boost Capacitors
The boost capacitors (C BST ) must be selected large
enough to handle the gate-charging requirements of
the high-side MOSFETs. Typically, 0.1μF ceramic
capacitors work well for low-power applications driving
medium-sized MOSFETs. However, high-current appli-
cations driving large, high-side MOSFETs require boost
capacitors larger than 0.1μF. For these applications,
?
?
? V IN ( MAX ) f SW
?
? I LOAD Q G ( SW )
I GATE
+
C OSS V IN ( MAX ) ?
2
select the boost capacitors to avoid discharging the
capacitor more than 200mV while charging the high-
side MOSFETs’ gates:
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).
C BST =
Q GATE
200 mV
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
where Q GATE is the total gate charge specified in the
high-side MOSFET’s data sheet. For example, assume
the FDS6612A n-channel MOSFET is used on the high
side. According to the manufacturer’s data sheet, a sin-
gle FDS6612A has a maximum gate charge of 13nC
______________________________________________________________________________________
31
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| MAX8745ETJ+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 |
| MAX874C/D | 功能描述:基准电压& 基准电流 RoHS:否 制造商:STMicroelectronics 产品:Voltage References 拓扑结构:Shunt References 参考类型:Programmable 输出电压:1.24 V to 18 V 初始准确度:0.25 % 平均温度系数（典型值）:100 PPM / C 串联 VREF - 输入电压（最大值）: 串联 VREF - 输入电压（最小值）: 分流电流（最大值）:60 mA 最大工作温度:+ 125 C 封装 / 箱体:SOT-23-3L 封装:Reel |
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