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参数资料
| 型号： | LTC3851IGN#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 20/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SSOP |
| 产品培训模块： | LTC3851 Single Output DC/DC Switching Regulator Controller |
| 特色产品： | Wide Input Voltage Range Synchronous Step-Down DC/DC Controller |
| 标准包装： | 2,500 |
| 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 ~ 125°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
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LTC3851
APPLICATIONS INFORMATION
The loop ?lter components, C LP and R LP , smooth out
the current pulses from the phase detector and provide
a stable input to the voltage-controlled oscillator. The
?lter components C LP and R LP determine how fast the
loop acquires lock. Typically R LP is 1k to 10k and C LP is
2200pF to 0.01μF.
When the external oscillator is active before the LTC3851
is enabled, the internal oscillator frequency will track the
external oscillator frequency as described in the preceding
paragraphs. In situations where the LTC3851 is enabled
before the external oscillator is active, a low free-running
oscillator frequency of approximately 50kHz will result. It is
possible to increase the free-running, pre-synchronization
frequency by adding a second resistor in parallel with
R LP and C LP . The second resistor will also cause a phase
difference between the internal and external oscillator
signals. The magnitude of the phase difference is inversely
proportional to the value of the second resistor.
The external clock (on MODE/PLLIN pin) input high
threshold is nominally 1.6V, while the input low threshold
is nominally 1.2V.
Minimum On-Time Considerations
Minimum on-time t ON(MIN) is the smallest time duration
that the LTC3851 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:
amount of cycle skipping can occur with correspondingly
larger current and voltage ripple.
Ef?ciency Considerations
The percent ef?ciency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the ef?ciency and which change would
produce the most improvement. Percent ef?ciency can
be expressed as:
%Ef?ciency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3851 circuits: 1) IC V IN current, 2) INTV CC
regulator current, 3) I 2 R losses, 4) topside MOSFET
transition losses.
1. The V IN current is the DC supply current given in the
Electrical Characteristics table, which excludes MOSFET
driver current. V IN current typically results in a small
(<0.1%) loss.
2. INTV CC current is the sum of the MOSFET driver and
control currents. The MOSFET driver current results
from switching the gate capacitance of the power
MOSFETs. Each time a MOSFET gate is switched from
low to high to low again, a packet of charge dQ moves
from INTV CC to ground. The resulting dQ/dt is a current
t ON(MIN) <
V OUT
V IN (f)
out of INTV CC that is typically much larger than the
control circuit current. In continuous mode, I GATECHG
= f(Q T + Q B ), where Q T and Q B are the gate charges of
If the duty cycle falls below what can be accommodated
by the minimum on-time, the controller will begin to skip
cycles. The output voltage will continue to be regulated,
but the ripple voltage and current will increase.
The minimum on-time for the LTC3851 is approximately
90ns. However, as the peak sense voltage decreases the
minimum on-time gradually increases. This is of particu-
lar concern in forced continuous applications with low
ripple current at light loads. If the duty cycle drops below
the minimum on-time limit in this situation, a signi?cant
20
the topside and bottom side MOSFETs.
3. I 2 R losses are predicted from the DC resistances of
the fuse (if used), MOSFET, inductor and current sense
resistor. In continuous mode, the average output current
?ows through L and R SENSE , but is “chopped” between
the topside MOSFET and the synchronous MOSFET. If
the two MOSFETs have approximately the same R DS(ON) ,
then the resistance of one MOSFET can simply be
summed with the resistances of L and R SENSE to obtain
I 2 R losses. For example, if each R DS(ON) = 10mΩ, DCR
= 10mΩ and R SENSE = 5mΩ, then the total resistance
3851fb
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3851IMSE#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) |
| LTC3851IMSE#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) |
| LTC3851IMSE-1#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) |
| LTC3851IMSE-1#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) |
| LTC3851IUD#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) |
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