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| 型号： | LTC3851EMSE-1#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-MSOP |
| 特色产品： | Wide Input Voltage Range Synchronous Step-Down DC/DC Controller |
| 标准包装： | 37 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 790kHz |
| 占空比： | 99% |
| 电源电压： | 4 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 ~ 85°C |
| 封装/外壳： | 16-TFSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3851-1
APPLICATIONS INFORMATION
is low. When the topside MOSFET is to be turned on, the
driver places the C B 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 V IN
and the BOOST pin follows. With the topside MOSFET on,
the boost voltage is above the input supply:
V BOOST = V IN + V INTVCC
The value of the boost capacitor C B needs to be 100 times
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.
C OUT Selection
The selection of C OUT is primarily determined by the
effective series resistance, ESR, to minimize voltage
ripple. The output ripple, ΔV OUT , in continuous mode is
determined by:
that of the total input capacitance of the topside MOSFET.
The reverse breakdown of the external Schottky diode
must be greater than V IN(MAX) .
?
Δ V OUT ≈ Δ I L ? ESR +
?
1 ?
?
8 fC OUT ?
C OUT SENSE
Undervoltage Lockout
The LTC3851-1 has two functions that help protect the
controller in case of undervoltage conditions. A precision
UVLO comparator constantly monitors the INTV CC voltage
to ensure that an adequate gate-drive voltage is present.
It locks out the switching action when INTV CC is below
3.2V. To prevent oscillation when there is a disturbance
on the INTV CC , the UVLO comparator has 400mV of preci-
sion hysteresis.
where f = operating frequency, C OUT = output capacitance
and ΔI L = ripple current in the inductor. The output ripple is
highest at maximum input voltage since ΔI L increases with
input voltage. Typically, once the ESR requirement for C OUT
has been met, the RMS current rating generally far exceeds
the I RIPPLE(P-P) requirement. With ΔI L = 0.3I OUT(MAX) and
allowing 2/3 of the ripple to be due to ESR, the output
ripple will be less than 50mV at maximum V IN and:
Required ESR < 2.2R
Another way to detect an undervoltage condition is to
monitor the V IN supply. Because the RUN pin has a precision
turn-on reference of 1.25V, one can use a resistor divider
C OUT >
1
8 fR SENSE
to V IN to turn on the IC when V IN is high enough.
C IN Selection
In continuous mode, the source current of the top N-channel
MOSFET is a square wave of duty cycle V OUT /V IN . 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:
The ?rst condition relates to the ripple current into the ESR
of the output capacitance while the second term guarantees
that the output capacitance does not signi?cantly discharge
during the operating frequency period due to ripple current.
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 I TH pin
? V IN
I RMS O ( MAX ) OUT ?
– 1 ?
? I
V
V IN ? V OUT
?
?
1 / 2
OPTI-LOOP compensation components can be optimized
to provide stable, high performance transient response
regardless of the output capacitors selected.
This formula has a maximum at V IN = 2V OUT , where I RMS =
I O(MAX) /2. This simple worst-case condition is commonly
used for design because even signi?cant 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
The selection of output capacitors for applications with
large load current transients is primarily determined by the
voltage tolerance speci?cations 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.
to choose a capacitor rated at a higher temperature than
38511fa
17
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相关代理商/技术参数 |
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| LTC3851EUD#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:- 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 |
| LTC3851EUD#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) |
| LTC3851EUD-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) |
| LTC3851EUD-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) |
| LTC3851IGN#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:- 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) |
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