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参数资料
| 型号： | MAX1865TEEP+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 20/25页 |
| 文件大小： | 0K |
| 描述： | IC PWR SUPPLY CONTROLLER 20QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 应用： | 电源控制器 |
| 输入电压： | 4.5 V ~ 28 V |
| 电流 - 电源： | 1.4mA |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 20-QSOP |
| 包装： | 带卷 (TR) |
xDSL/Cable Modem Triple/Quintuple Output
Power Supplies
? V T ? ? ?
? LOAD ? ? ?
Transistor Selection
The pass transistors must meet specifications for cur-
rent gain (h FE ), input capacitance, collector-emitter sat-
uration voltage, and power dissipation. The transistor’s
current gain limits the guaranteed maximum output cur-
? 5 . 5 ? ? ? I BIAS h FE ? ?
A V ( LDO ) ≈ ? ? ? 1 + ? I ? ? V REF
where V T is 26mV, and I BIAS is the current through the
I LOAD ( MAX ) = ? I DRV - ? BE ? ? h FE ( MIN )
rent to:
? ? V ? ?
? ?
? ? R BE ? ?
base-to-emitter resistor (R BE ). This bias resistor is typical-
ly 220 Ω , providing approximately 3.2mA of bias current.
The output capacitor creates the dominant pole.
However, the pass transistor’s input capacitance creates
a second pole in the system. Additionally, the output
where I DRV is the minimum base-drive current, and R BE
(220 Ω ) 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 Stability Requirements ), so excessive
gain will destabilize the output. Therefore, transistors
with current gain over 100 at the maximum output cur-
capacitor’s ESR generates a zero, which may be used to
cancel the second pole if necessary. Therefore, to
achieve stable operation, use the following equations to
verify that the linear regulator is properly compensated:
1) First, determine the dominant pole set by the linear
regulator’s output capacitor and the load resistor:
rent, such as Darlington transistors, are not recom-
mended. The transistor’s input capacitance and input
resistance also create a second pole, which could be
? POLE ( CLDO ) =
1
2 π C LDO R LOAD
=
I LOAD ( MAX )
2 π C LDO V LDO
low enough to destabilize the output when heavily
P = I LOAD ( MAX ) ( V LDOIN OUT ) = I LOAD ( MAX ) V CE
? POLE ( CBE ) =
( )
=
loaded.
The transistor’s saturation voltage at the maximum out-
put current determines the minimum input-to-output
voltage differential that the linear regulator will support.
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-
pated equals the maximum load current times the maxi-
mum input-to-output voltage differential:
- V
Stability Requirements
The MAX1864/MAX1865 linear regulators use an inter-
Unity Gain Crossover = A V ( LDO ) ? POLE ( CLDO )
2) Next, determine the second pole set by the base-to-
emitter capacitance (including the transistor’s input
capacitance), the transistor’s input resistance, and
the base-to-emitter pullup resistor:
1
2 π C BE R BE || R IN ( NPN )
R BE I LOAD + V T h FE
2 π C BE R BE V T h FE
3) A third pole is set by the linear regulator’s feedback
resistance and the capacitance between FB_ and
GND, including 20pF stray capacitance:
nal transconductance amplifier to drive an external
pass transistor. The transconductance amplifier, pass
transistor’s specifications, the base-emitter resistor,
? POLE ( FB ) =
1
2 π C FB ( R 1 || R 2 )
and the output capacitor determine the loop stability. If
the output capacitor and pass transistor are not proper-
ly selected, the linear regulator will be unstable.
The transconductance amplifier regulates the output
voltage by controlling the pass transistor’s base cur-
rent. Since the output voltage is a function of the load
current and load resistance, the total DC loop gain
(A V(LDO) ) is approximately:
4) If the second and third poles occur well after unity-
gain crossover, the linear regulator will remain stable:
? POLE ( CBE ) > 2 ? POLE ( CLDO ) A V ( LDO )
However, if the ESR zero occurs before unity-gain
crossover, cancel the zero with ? POLE(FB) by changing
circuit components such that:
20
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相关代理商/技术参数 |
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| MAX1865UEEP | 功能描述:电流和电力监控器、调节器 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 |
| MAX1865UEEP-T | 功能描述:电流和电力监控器、调节器 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 |
| MAX1868EGL | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1868ETL | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1869EGL | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
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