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| 型号： | LTC3851EUD-1#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-QFN |
| 特色产品： | Wide Input Voltage Range Synchronous Step-Down DC/DC Controller |
| 标准包装： | 121 |
| 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-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3851-1
APPLICATIONS INFORMATION
The Typical Application on the ?rst page of this data sheet
is a basic LTC3851-1 application circuit. The LTC3851-1
can be con?gured to use either DCR (inductor resistance)
V IN
INTV CC
V IN
sensing or low value resistor sensing. The choice of the
two current sensing schemes is largely a design trade-off
between cost, power consumption and accuracy. DCR
sensing is becoming popular because it saves expensive
current sensing resistors and is more power ef?cient,
especially in high current applications. However, current
sensing resistors provide the most accurate current limits
BOOST
TG
SW
LTC3851-1
BG
GND
SENSE +
SENSE –
R SENSE
V OUT
for the controller. Other external component selection
is driven by the load requirement, and begins with the
selection of R SENSE (if R SENSE is used) and the inductor
FILTER COMPONENTS
PLACED NEAR SENSE PINS
38511 F01
value. Next, the power MOSFETs and Schottky diodes are
selected. Finally, input and output capacitors are selected.
The circuit shown on the ?rst page can be con?gured for
operation up to 40V at V IN .
Figure 1. Using a Resistor to Sense Current with the LTC3851-1
of 20% for variations in the IC and external component
values yields:
SENSE + and SENSE – Pins
The SENSE + and SENSE – pins are the inputs to the current
comparators. The common mode input voltage range of
R SENSE = 0 . 8 ?
V MAX
I MAX + Δ I L / 2
the current comparators is 0V to 5.5V. Both SENSE pins
are high impedance inputs with small base currents of
less than 1μA. When the SENSE pins ramp up from 0V
to 1.4V, the small base currents ?ow out of the SENSE
pins. When the SENSE pins ramp down from 5V to 1.1V,
the small base currents ?ow into the SENSE pins. The
high impedance inputs to the current comparators allow
accurate DCR sensing. However, care must be taken not
to ?oat these pins during normal operation.
Low Value Resistors Current Sensing
A typical sensing circuit using a discrete resistor is shown
in Figure 1. R SENSE is chosen based on the required output
current.
The current comparator has a maximum threshold,
V MAX = 50mV. The current comparator threshold sets the
maximum peak of the inductor current, yielding a maximum
average output current, I MAX , equal to the peak value less
Inductor DCR Sensing
For applications requiring the highest possible ef?ciency,
the LTC3851-1 is capable of sensing the voltage drop
across the inductor DCR, as shown in Figure 2. The
DCR of the inductor represents the small amount of
DC winding resistance of the copper, which can be less
than 1m Ω for today’s low value, high current inductors.
If the external R1||R2 ? C1 time constant is chosen to
be exactly equal to the L/DCR time constant, the voltage
drop across the external capacitor is equal to the voltage
drop across the inductor DCR multiplied by R2/(R1 + R2).
Therefore, R2 may be used to scale the voltage across the
sense terminals when the DCR is greater than the target
sense resistance. Check the manufacturer’s data sheet
for speci?cations regarding the inductor DCR, in order
to properly dimension the external ?lter components.
The DCR of the inductor can also be measured using a
good RLC meter.
half the peak-to-peak ripple current, ΔI L . Allowing a margin
38511fa
12
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相关代理商/技术参数 |
参数描述 |
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| 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) |
| LTC3851IGN#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) |
| 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) |
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