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| 型号： | MAX1771CSA+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 11/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM 8-SOIC |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 100 |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 92% |
| 电源电压： | 3 V ~ 16.5 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 产品目录页面： | 1410 (CN2011-ZH PDF) |
MAX1771
12V or Adjustable, High-Efficiency,
Low I Q , Step-Up DC-DC Controller
Power Transistor Selection
Use an N-channel MOSFET power transistor with the
MAX1771.
To ensure the external N-channel MOSFET (N-FET) is
turned on hard, use logic-level or low-threshold
N-FETs when the input drive voltage is less than 8V. This
applies even in bootstrapped mode, to ensure start-up.
N-FETs provide the highest efficiency because they do
not draw any DC gate-drive current.
When selecting an N-FET, three important parameters
are the total gate charge (Q g ), on-resistance (r DS(ON) ),
and reverse transfer capacitance (C RSS ).
Q g takes into account all capacitances associated with
charging the gate. Use the typical Q g value for best
results; the maximum value is usually grossly over-
specified since it is a guaranteed limit and not the mea-
sured value. The typical total gate charge should be
50nC or less. With larger numbers, the EXT pins may
not be able to adequately drive the gate. The EXT
rise/fall time varies with different capacitive loads as
shown in the Typical Operating Characteristics .
The two most significant losses contributing to the
N-FET’s power dissipation are I 2 R losses and switching
losses. Select a transistor with low r DS(ON) and low
C RSS to minimize these losses.
Determine the maximum required gate-drive current
from the Q g specification in the N-FET data sheet.
The MAX1771’s maximum allowed switching frequency
during normal operation is 300kHz; but at start-up, the
maximum frequency can be 500kHz, so the maximum
current required to charge the N-FET ’s gate is
f(max) x Q g (typ). Use the typical Q g number from the
transistor data sheet. For example, the Si9410DY has a
Q g (typ) of 17nC (at V GS = 5V), therefore the current
required to charge the gate is:
I GATE (max) = (500kHz) (17nC) = 8.5mA.
The bypass capacitor on V+ (C2) must instantaneously
furnish the gate charge without excessive droop (e.g.,
less than 200mV):
Q g
? V+ = ——
C2
Continuing with the example, ? V+ = 17nC/0.1μF = 170mV.
Figure 2a’s application circuit uses an 8-pin Si9410DY
surface-mount N-FET that has 50m ? on-resistance with
4.5V V GS , and a guaranteed V TH of less than 3V. Figure
2b’s application circuit uses an MTD20N03HDL logic-
level N-FET with a guaranteed threshold voltage (V TH )
of 2V.
Maxim Integrated
Diode Selection
The MAX1771’s high switching frequency demands a
high-speed rectifier. Schottky diodes such as the
1N5817 –1N5822 are recommended. Make sure the
Schottky diode’s average current rating exceeds the
peak current limit set by R SENSE , and that its break-
down voltage exceeds V OUT . For high-temperature
applications, Schottky diodes may be inadequate due
to their high leakage currents; high-speed silicon
diodes such as the MUR105 or EC11FS1 can be used
instead. At heavy loads and high temperatures, the
benefits of a Schottky diode’s low forward voltage may
outweigh the disadvantages of its high leakage current.
Capacitor Selection
Output Filter Capacitor
The primary criterion for selecting the output filter capac-
itor (C4) is low effective series resistance (ESR). The
product of the peak inductor current and the output filter
capacitor’s ESR determines the amplitude of the ripple
seen on the output voltage. Two OS-CON 150μF, 16V
output filter capacitors in parallel with 35m ? of ESR each
typically provide 75mV ripple when stepping up from 5V
to 12V at 500mA (Figure 2a). Smaller-value and/or high-
er-ESR capacitors are acceptable for light loads or in
applications that can tolerate higher output ripple.
Since the output filter capacitor’s ESR affects efficien-
cy, use low-ESR capacitors for best performance. See
Table 1 for component selection.
Input Bypass Capacitors
The input bypass capacitor (C1) reduces peak currents
drawn from the voltage source and also reduces noise
at the voltage source caused by the switching action of
the MAX1771. The input voltage source impedance
determines the size of the capacitor required at the V+
input. As with the output filter capacitor, a low-ESR
capacitor is recommended. For output currents up to
1A, 68μF (C1) is adequate, although smaller bypass
capacitors may also be acceptable.
Bypass the IC with a 0.1μF ceramic capacitor (C2)
placed as close to the V+ and GND pins as possible.
Reference Capacitor
Bypass REF with a 0.1μF capacitor (C3). REF can
source up to 100μA of current for external loads.
Feed-Forward Capacitor
In adjustable output voltage and non-bootstrapped
modes, parallel a 47pF to 220pF capacitor across R2,
as shown in Figures 2 and 3. Choose the lowest capac-
itor value that insures stability; high capacitance values
may degrade line regulation.
11
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1771CSA+ | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up 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 |
| MAX1771CSA+T | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up 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 |
| MAX1771CSA+TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1771CSA-G05 | 功能描述:DC/DC 开关控制器 12/Adj V Low IQ Step-Up 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 |
| MAX1771CSAT | 制造商:MAXIM 功能描述:DC/DC SWITCHING CONTROLLERS |
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