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参数资料
| 型号： | LTC3851AEMSE#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PDSO16 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件页数： | 9/30页 |
| 文件大小： | 430K |
| 代理商： | LTC3851AEMSE#PBF |
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LTC3851A
17
3851afa
applicaTions inForMaTion
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 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.
Another way to detect an undervoltage condition is to
monitor the VIN supply. Because the RUN pin has a preci-
sion 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-
channel 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 offer much relief. Note that capacitor
manufacturers’ 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. Several capacitors may
also be paralleled to meet 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,ΔVOUT,incontinuousmodeisdeterminedby:
ΔVOUT ≈ ΔIL ESR+
1
8fCOUT
where f = operating frequency, COUT = output capacitance
and ΔIL = ripple current in the inductor. The output ripple
is highest at maximum input voltage since ΔIL increases
with input voltage. Typically, once the ESR require-
ment for COUT has been met, the RMS current rating
generally far exceeds the IRIPPLE(P-P) requirement. With
ΔIL = 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 if the ILIM pin is configured to float 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 |
|---|---|
| LTC3851AEUD#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3851AEUD#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3851AEUD-1#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3851AEUD-1#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-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) |
| LTC3851AHMSE#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:- 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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