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| 型号： | LTC3855IFE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 27/44页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 38-SSOP |
| 标准包装： | 50 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 850kHz |
| 占空比： | 95% |
| 电源电压： | 4.5 V ~ 38 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： | -40°C ~ 125°C |
| 封装/外壳： | 38-TFSOP （0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 管件 |
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LTC3855
APPLICATIONS INFORMATION
FREQ PIN VOLTAGE (V)
DETECTOR
t ON(MIN) <
Phase-LockedLoopandFrequencySynchronization
The LTC3855 has a phase-locked loop (PLL) comprised of
an internal voltage-controlled oscillator (V CO ) and a phase
detector. This allows the turn-on of the top MOSFET of
controller 1 to be locked to the rising edge of an external
clock signal applied to the MODE/PLLIN pin. The turn-on
of controller 2’s top MOSFET is thus 180 degrees out-
of-phase with the external clock. The phase detector is
an edge sensitive digital type that provides zero degrees
phase shift between the external and internal oscillators.
This type of phase detector does not exhibit false lock to
harmonics of the external clock.
The output of the phase detector is a pair of complementary
current sources that charge or discharge the internal filter
network. There is a precision 10μA of current flowing out
of FREQ pin. This allows the user to use a single resistor
to SGND to set the switching frequency when no external
clock is applied to the MODE/PLLIN pin. The internal switch
between FREQ pin and the integrated PLL filter network
is ON, allowing the filter network to be pre-charged to the
same voltage potential as the FREQ pin. The relationship
between the voltage on the FREQ pin and the operating
frequency is shown in Figure 12 and specified in the Elec-
trical Characteristic table. If an external clock is detected
on the MODE/PLLIN pin, the internal switch mentioned
above will turn off and isolate the influence of FREQ pin.
Note that the LTC3855 can only be synchronized to an
external clock whose frequency is within range of the
LTC3855’s internal V CO . This is guaranteed to be between
250kHz and 770kHz. A simplified block diagram is shown
in Figure 13.
If the external clock frequency is greater than the internal
oscillator’s frequency, f OSC , then current is sourced continu-
ously from the phase detector output, pulling up the filter
network. When the external clock frequency is less than f OSC ,
current is sunk continuously, pulling down the filter network. If
the external and internal frequencies are the same but exhibit
a phase difference, the current sources turn on for an amount
of time corresponding to the phase difference. The voltage on
the filter network is adjusted until the phase and frequency of
the internal and external oscillators are identical. At the stable
operating point, the phase detector output is high impedance
and the filter capacitor holds the voltage.
900
800
700
600
500
400
300
200
100
0
0 0.5 1 1.5 2 2.5
3855 F12
Figure 12. Relationship Between Oscillator
Frequency and Voltage at the FREQ Pin
2.4V 5V
R SET
10μA
FREQ
MODE/
PLLIN DIGITAL
EXTERNAL PHASE/ SYNC
OSCILLATOR FREQUENCY
VCO
3855 F13
Figure 13. Phase-Locked Loop Block Diagram
Typically, the external clock (on MODE/PLLIN pin)
input high threshold is 1.6V, while the input low threshold
is 1V. It is not recommended to apply the external clock
when IC is in shutdown.
Minimum On-Time Considerations
Minimum on-time t ON(MIN) is the smallest time duration
that the LTC3855 is capable of turning on the top MOSFET.
It is determined by internal timing delays and the gate
charge required to turn on the top MOSFET. Low duty
cycle applications may approach this minimum on-time
limit and care should be taken to ensure that
V OUT
V IN (f)
3855f
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3855IUJ#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 |
| LTC3855IUJ#PBF-ES | 制造商:Linear Technology 功能描述: |
| LTC3855IUJ#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® 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) |
| LTC3856EFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 38TFSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:2,000 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:1MHz 占空比:50% 电源电压:9 V ~ 10 V 降压:无 升压:是 回扫:是 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:8-TSSOP（0.173"，4.40mm 宽） 包装:带卷 (TR) |
| LTC3856EFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 38TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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) |
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