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| 型号： | LTC1261IS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/18页 |
| 文件大小： | 0K |
| 描述： | IC REG SWITCHD CAP INV ADJ 8SOIC |
| 标准包装： | 100 |
| 类型： | 切换式电容器（充电泵），反相 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | -1.25 V ~ -8 V |
| 输入电压： | 3 V ~ 8 V |
| 频率 - 开关： | 550kHz |
| 电流 - 输出： | 15mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 8-SOIC |
LTC1261
APPLICATIONS INFORMATION
LOW ESR V OUT
V OUT AVERAGE
pumptoresponduntilthenextclockedge.Thisprevents
the charge pump from going into very high frequency
oscillation under such conditions but it also creates an
output error as the feedback loop regulates based on
the top of the spike, not the average value of the output
(Figure 5). The resulting output voltage behaves as if a
resistor of value C ESR ? (I PK /I AVE )Ω was placed in series
with the output. To avoid this nasty sequence of events
connect a 0.1μF ceramic capacitor in parallel with the
larger output capacitor. The ceramic capacitor will “eat”
the high frequency spike, preventing it from fooling the
feedback loop, while the larger but slower tantalum or
aluminum output capacitor supplies output current to the
load between charge cycles.
CLOCK
V SET
OUTPUT CAP
COMP1
OUTPUT
V SET
Most of this resistance is already provided by the internal
switches in the LTC1261 (especially in tripler mode). More
than 1Ω or 2Ω of ESR on the flying capacitors will start
to affect the regulation at maximum load.
RESISTOR SELECTION
Resistor selection is easy with the fixed output versions
of the LTC1261— no resistors are needed! Selecting
the right resistors for the adjustable parts is only a little
more difficult. A resistor divider should be used to divide
the signal at the output to give 1.24V at the ADJ pin with
respect to V OUT (Figure 6). The LTC1261 uses a positive
reference with respect to V OUT , not a negative reference
with respect to ground (Figure 2 shows the reference con-
nection). Be sure to keep this in mind when connecting
the resistors! If the initial output is not what you expected,
try swapping the two resistors.
6 (4*)
GND
LTC1261 R1
10 (5*)
ADJ
(
)
OUT V OUT = –1.24V
HIGHESR
OUTPUT CAP
V OUT
V OUT
AVERAGE
COMP1
OUTPUT
LTC1261 ? F05
R2
11 (6*) R1 + R2
R2
*LTC1261CS8
LTC1261 ? F06
Figure 6. External Resistor Connections
Figure 5. Output Ripple with Low and High ESR Capacitors
Note that ESR in the flying capacitors will not cause the
same condition; in fact, it may actually improve the situ-
ation by cutting the peak current and lowering the ampli-
tude of the spike. However, more flying capacitor ESR is
not necessarily better. As soon as the RC time constant
approaches half of a clock period (the time the capaci-
tors have to share charge at full duty cycle) the output
current capability of the LTC1261 will begin to diminish.
For 0.1μF flying capacitors, this gives a maximum total
series resistance of:
The 14-lead adjustable parts include a built-in resistor
string which can provide an assortment of output voltages
by using different pin-strapping options at the R0, R1,
and R ADJ pins (Table 2). The internal resistors are roughly
124k, 226k, 100k, and 50k (see Figure 2) giving output
options of –3.5V, –4V, –4.5V, and –5V. The resistors
are carefully matched to provide accurate divider ratios,
but the absolute values can vary substantially from part
to part. It is not a good idea to create a divider using an
external resistor and one of the internal resistors unless
the output voltage accuracy is not critical.
? ? = 2 ? ? 550kHz ? ? / 0.1μF = 9.1 ?
1 ? t CLK ? 1 ? 1 ?
?
2 ? C FLY
1261fb
10
For more information www.linear.com/LTC1261
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相关代理商/技术参数 |
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| LTC1261LCMS8 | 功能描述:IC REG SWITCHD CAP INV ADJ 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1261LCMS8#PBF | 功能描述:IC REG SWITCHD CAP INV ADJ 8MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LTC1261LCMS8#TR | 功能描述:IC REG SWITCHD CAP INV ADJ 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1261LCMS8#TRPBF | 功能描述:IC REG SWITCHD CAP INV ADJ 8MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
| LTC1261LCMS8-4 | 功能描述:IC REG SWITCHD CAP INV -4V 8MSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
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