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| 型号： | MAX871EUK+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 5/8页 |
| 文件大小： | 0K |
| 描述： | IC VOLT INVERT SW CAP SOT23-5 |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 1 |
| 应用： | 充电泵，LCD |
| 输入电压： | 1.4 V ~ 5.5 V |
| 输出数： | 1 |
| 输出电压： | -1.4 V ~ -5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SC-74A，SOT-753 |
| 供应商设备封装： | SOT-23-5 |
| 包装： | 标准包装 |
| 其它名称： | MAX871EUK+TDKR |
Switched-Capacitor Voltage Inverters
_______________Detailed Description
The MAX870/MAX871 capacitive charge pumps invert
the voltage applied to their input. For highest perfor-
mance, use low equivalent series resistance (ESR)
capacitors (e.g., ceramic).
During the first half-cycle, switches S2 and S4 open,
switches S1 and S3 close, and capacitor C1 charges to
IN
S1
C1
S2
the voltage at IN (Figure 2). During the second half-
cycle, S1 and S3 open, S2 and S4 close, and C1 is level
shifted downward by V IN volts. This connects C1 in par-
S3
S4
C2
V OUT = -(V IN )
allel with the reservoir capacitor C2. If the voltage across
C2 is smaller than the voltage across C1, then charge
flows from C1 to C2 until the voltage across C2 reaches
-V IN . The actual voltage at the output is more positive
than -V IN , since switches S1–S4 have resistance and the
load drains charge from C2.
Charge-Pump Output
The MAX870/MAX871 are not voltage regulators: the
charge pump’s output source resistance is approxi-
mately 20 ? at room temperature (with V IN = +5V), and
Figure 2. Ideal Voltage Inverter
where the output impedance is roughly approximated
by:
V OUT approaches -5V when lightly loaded. V OUT will
droop toward GND as load current increases. The
droop of the negative supply (V DROOP- ) equals the cur-
rent draw from OUT (I OUT ) times the negative convert-
R OUT ?
1
( f OSC )
x C 1
+ 2 R SW + 4 ESR C 1 + ESR C 2
er’s source resistance (RS-):
V DROOP- = I OUT x RS-
The negative output voltage will be:
V OUT = -(V IN – V DROOP- )
Efficiency Considerations
The efficiency of the MAX870/MAX871 is dominated by
its quiescent supply current (I Q ) at low output current
and by its output impedance (R OUT ) at higher output
current; it is given by:
The first term is the effective resistance of an ideal
switched-capacitor circuit (Figures 3a and 3b), and
R SW is the sum of the charge pump’s internal switch
resistances (typically 8 ? to 9 ? at V IN = +5V). The typical
output impedance is more accurately determined from
the Typical Operating Characteristics .
__________Applications Information
Capacitor Selection
? 1 ?
?
?
η?
I OUT ?
I OUT + I Q ?
I OUT × R OUT ?
V IN
To maintain the lowest output resistance, use capacitors
with low ESR (Table 1). The charge-pump output resis-
tance is a function of C1’s and C2’s ESR. Therefore,
minimizing the charge-pump capacitor’s ESR minimizes
the total output resistance.
f
R EQUIV
V+
V OUT
V+
V OUT
C1
C2
R L
R EQUIV =
1
f × C1
C2
R L
Figure 3a. Switched-Capacitor Model
Figure 3b. Equivalent Circuit
_______________________________________________________________________________________
5
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相关代理商/技术参数 |
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| MAX8720EEI+ | 功能描述:DC/DC 开关控制器 Dyn Adj 6-Bit VID Step-Down 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 |
| MAX8720EEI+T | 功能描述:DC/DC 开关控制器 Dyn Adj 6-Bit VID Step-Down 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 |
| MAX8720EEI-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 |
| MAX8720ETX | 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 |
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