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参数资料
| 型号： | LTC3851AMPMSE-1#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 0.05 A SWITCHING CONTROLLER, 810 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件页数： | 10/30页 |
| 文件大小： | 0K |
| 代理商： | LTC3851AMPMSE-1#TRPBF |
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LTC3851A-1
18
3851a1fa
applicaTions inForMaTion
is low. When the topside MOSFET is to be turned on, the
driver places the CB voltage across the gate source of the
MOSFET. This enhances the MOSFET and turns on the
topside switch. The switch node voltage, SW, rises to VIN
and the BOOST pin follows. With the topside MOSFET on,
the boost voltage is above the input supply:
VBOOST = VIN + VINTVCC
The value of the boost capacitor, CB, needs to be 100 times
that of the total input capacitance of the topside MOSFET.
The reverse breakdown of the external Schottky diode
must be greater than VIN(MAX).
Undervoltage Lockout
The LTC3851A-1 has two functions that help protect the
controller in case of undervoltage conditions. A precision
UVLO comparator constantly monitors the INTVCCvoltage
to ensure that an adequate gate-drive voltage is present.
It locks out the switching action when INTVCC is below
3.2V. To prevent oscillation when there is a disturbance
on the INTVCC, the UVLO comparator has 400mV of preci-
sion hysteresis.
Anotherwaytodetectanundervoltageconditionistomoni-
tor the VIN supply. Because the RUN pin has a precision
turn-on reference of 1.22V, one can use a resistor divider
to VIN to turn on the IC when VIN is high enough.
CIN Selection
In continuous mode, the source current of the top N-chan-
nel MOSFET is a square wave of duty cycle VOUT/VIN. To
prevent large voltage transients, a low ESR input capacitor
sized for the maximum RMS current must be used. The
maximum RMS capacitor current is given by:
IRMS IO(MAX)
VOUT
VIN
VOUT
– 1
1/2
This formula has a maximum at VIN = 2VOUT, where IRMS =
IO(MAX)/2. This simple worst-case condition is commonly
used for design because even significant deviations do not
offermuchrelief.Notethatcapacitormanufacturers’ripple
current ratings are often based on only 2000 hours of life.
This makes it advisable to further derate the capacitor or
to choose a capacitor rated at a higher temperature than
required.Severalcapacitorsmayalsobeparalleledtomeet
size or height requirements in the design. Always consult
the manufacturer if there is any question.
COUT Selection
The selection of COUT is primarily determined by the effec-
tive series resistance, ESR, to minimize voltage ripple. The
outputripple,VOUT,incontinuousmodeisdeterminedby:
VOUT ≈ IL ESR+
1
8fCOUT
where f = operating frequency, COUT = output capacitance
and IL = ripple current in the inductor. The output ripple
is highest at maximum input voltage since IL increases
with input voltage. Typically, once the ESR requirement
for COUT has been met, the RMS current rating gener-
ally far exceeds the IRIPPLE(P-P) requirement. With IL =
0.3IOUT(MAX) and allowing 2/3 of the ripple to be due to
ESR, the output ripple will be less than 50mV at maximum
VIN and:
COUT Required ESR < 2.2RSENSE
COUT >
1
8fRSENSE
The first condition relates to the ripple current into the ESR
oftheoutputcapacitancewhilethesecondtermguarantees
thattheoutputcapacitancedoesnotsignificantlydischarge
duringtheoperatingfrequencyperiodduetoripplecurrent.
The choice of using smaller output capacitance increases
the ripple voltage due to the discharging term but can be
compensated for by using capacitors of very low ESR to
maintain the ripple voltage at or below 50mV. The ITH pin
OPTI-LOOP compensation components can be optimized
to provide stable, high performance transient response
regardless of the output capacitors selected.
The selection of output capacitors for applications with
largeloadcurrenttransientsisprimarilydeterminedbythe
voltage tolerance specifications of the load. The resistive
component of the capacitor, ESR, multiplied by the load
current change, plus any output voltage ripple must be
within the voltage tolerance of the load.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3851EGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| LTC3851EGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP 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) |
| LTC3851EMSE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
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| LTC3851EMSE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-MSOP 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) |
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