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参数资料
| 型号： | MAX8744AETJ+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 |
| 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 = I LIMIT ? ?
? Δ I INDUCTOR ?
?
?
?
I LOAD ( MAX ) = ? I DRV ? V BE ? β MIN
C BST =
C BST = = 0 . 065 μ F
R 5 = R 6 ? OUTA ? 1 ?
A V ( LDO ) = ?
? ? 1 + I
? V T ? ?
LOAD ?
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,
select the boost capacitors to avoid discharging the
capacitor more than 200mV while charging the high-
side MOSFETs’ gates:
Q GATE
200 mV
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
(V GS = 5V). Using the above equation, the required
boost capacitance would be:
13 nC
200 mV
Selecting the closest standard value, this example
requires a 0.1μF ceramic capacitor.
LDOA Design Procedure
Output Voltage Selection
Adjust the auxiliary linear regulator’s output voltage by
connecting a resistive divider between OUTA and ana-
log ground with the center tap connected to FBA
(Figure 1). Select R6 in the 10k Ω to 30k Ω range, and
calculate R5 with the following equation:
? V ?
? V FBA ?
where V FBA = 1.0V.
Transistor Selection
The pass transistor must meet specifications for current
gain ( β ), input capacitance, collector-emitter saturation
voltage, and power dissipation. The transistor’s current
gain limits the guaranteed maximum output current to:
? ?
? R BE ?
where I DRV is the minimum guaranteed base drive cur-
rent, V BE is the base-to-emitter voltage of the transistor,
and R BE is the pullup resistor connected between the
transistor’s base and emitter. Furthermore, the transis-
tor’s current gain increases the linear regulator’s DC
loop gain (see the LDOA Stability Requirements sec-
tion), so excessive gain destabilizes the output.
Therefore, transistors with current gain over 100 at the
maximum output current can be difficult to stabilize and
are not recommended. The transistor’s input capaci-
tance and input resistance also create a second pole,
which could be low enough to make the output unsta-
ble when heavily loaded.
The transistor’s saturation voltage at the maximum out-
put current determines the minimum input-to-output
voltage differential that the linear regulator supports.
Alternatively, the package’s power dissipation could
limit the useable maximum input-to-output voltage dif-
ferential. The maximum power dissipation capability of
the transistor’s package and mounting must exceed the
actual power dissipation in the device. The power dissi-
pation equals the maximum load current times the max-
imum input-to-output differential:
PWR = I LOAD(MAX) (V INA -V OUTA )
PWR = I LOAD(MAX) V CE
LDOA Stability Requirements
The MAX8744A/MAX8745A linear-regulator controller
uses an internal transconductance amplifier to drive an
external pnp pass transistor. The transconductance
amplifier, the pass transistor, the base-to-emitter resistor,
and the output capacitor determine the loop stability.
The transconductance amplifier regulates the output
voltage by controlling the pass transistor’s base cur-
rent. The total DC loop gain is approximately:
? 5 . 5 V ? ? I BIAS h FE ?
?
where V T is 26mV at room temperature, h FE is the pass
transistor’s DC gain, and I BIAS is the current through
the base-to-emitter resistor (R BE ). The 680 Ω base-to-
emitter resistor used in Figure 1 was chosen to provide
a 1mA bias current (I BIAS ).
______________________________________________________________________________________
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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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