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| 型号： | LTC3852EUDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 23/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR DOUBLER PWM 24-QFN |
| 标准包装： | 73 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 810kHz |
| 占空比： | 99% |
| 电源电压： | 2.7 V ~ 38 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 是 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3852
APPLICATIONS INFORMATION
V RIPPLE(P ? P) ?
Effective Open Loop Output Resistance (R OL )
The effective open loop output resistance (R OL ) of a charge
pump is a very important parameter which determines the
strength of the charge pump. The value of this parameter
depends on many factors such as the oscillator frequency
(f OSC ), value of the ?ying capacitor (C FLY ), the nonoverlap
time, the internal switch resistances (R S ), and the ESR of
the external capacitors. A ?rst order approximation for
R OL is given below:
higher minimum turn-on time. The peak-to-peak output
ripple of a charge pump is approximately given by the
expression:
I PUMP
2f OSC ?C PUMP
where f OSC is the charge pump frequency (typically 1.2MHz)
and C PUMP is the value of the V PUMP storage capacitor.
Also, the value and style of the C PUMP capacitor can
R OL ? 2 ∑ R S +
S=1 TO 4
1
f OSC ?C FLY
signi?cantly affect the stability of the charge pump. As
shown in the Functional Diagram, the charge pump
uses a linear control loop to adjust the strength of the
Typical R OL values as a function of temperature are shown
in Figure 11.
charge pump to match the current required at the output.
The error signal of this loop is stored directly on the
8
7
6
V IN = 2.7V
V PUMP = 4.5V
output storage capacitor. This output capacitor also
serves to form the dominant pole of the control loop.
To prevent ringing or instability on the charge pump,
it is important to maintain at least 1μF of capacitance over
all conditions.
Excessive ESR on the C PUMP capacitor can degrade the
5
4
–50
0
50
100
loop stability of the charge pump. Its closed loop output
resistance is designed to be 0.5 W . For a 50mA load current
change, the output voltage will change by about 25mV. If
the output capacitor has 0.5 W or more of ESR, the closed
loop frequency response will cease to roll off in a simple
TEMPERATURE ( C)
3852 F11
one-pole fashion and poor load transient response or
Figure 11. Typical R OL vs Temperature
Charge Pump Capacitor Selection
The style and value of capacitors used with the charge
pump determine several important parameters such as
regulator control loop stability, output ripple, charge pump
strength and minimum start-up time.
To reduce noise and ripple, it is recommended that low
ESR (<0.1 W ) ceramic capacitors be used for both C IN
and C PUMP . These capacitors should be 2.2μF or greater.
Tantalum and aluminum capacitors are not recommended
because of their high ESR.
The value of C PUMP directly controls the amount of
output ripple for a given load current. Increasing the size
of C PUMP will reduce the output ripple at the expense of
instability could result. Ceramic capacitors typically have
exceptional ESR performance and combined with a good
board layout should yield very good stability and load
transient performance.
As the value of C PUMP controls the amount of output ripple,
the value of C IN controls the amount of ripple present at
the input pin (V IN1 ). The input current to the charge pump
will be relatively constant during the input charging phase
or the output charging phase but will drop to zero during
the nonoverlap times. Since the nonoverlap time is small
(~25ns), these missing notches will result in only a small
perturbation on the input power supply line. Note that a
higher ESR capacitor such as tantalum will have higher
input noise due to the voltage drop in the ESR. Therefore,
ceramic capacitors are again recommended for their
exceptional ESR performance.
3852f
23
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| LTC3852IUDD#PBF | 功能描述:IC REG CTRLR DOUBLER PWM 24-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 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:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3852IUDD#TRPBF | 功能描述:IC REG CTRLR DOUBLER PWM 24-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 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:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3853EUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC3853EUJ#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC3853EUJPBF | 制造商:Linear Technology 功能描述:DC-DC Controller Triple Buck 24V QFN40 |
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