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| 型号： | LTC3879EUD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-QFN |
| 标准包装： | 121 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 2MHz |
| 占空比： | 90% |
| 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 |
| 产品目录页面： | 1336 (CN2011-ZH PDF) |
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LTC3879
APPLICATIONS INFORMATION
The basic LTC3879 application circuit is shown on the ?rst
page of this data sheet. External component selection is
largely determined by maximum load current and begins
with the selection of sense resistance and power MOSFET
switches. The LTC3879 uses the on-resistance of the syn-
chronous power MOSFET to determine the inductor current.
The desired ripple current and operating frequency largely
determines the inductor value. Finally, C IN is selected for its
ability to handle the large RMS current into the converter,
and C OUT is chosen with low enough ESR to meet output
voltage ripple and transient speci?cations.
The gate drive voltages are set by the 5.3V INTV CC supply.
Consequently, logic-level threshold MOSFETs must be used
in LTC3879 applications. If the input voltage is expected
to drop below 5V, then sub-logic level threshold MOSFETs
should be considered.
Using the bottom MOSFET as the current sense element
requires particular attention be paid to its on-resistance.
MOSFET on-resistance is typically speci?ed with a maxi-
mum value R DS(ON)(MAX) at 25°C. In this case additional
margin is required to accommodate the rise in MOSFET
on-resistance with temperature.
Maximum V DS Sense Voltage and V RNG Pin
Inductor current is measured by sensing the bottom
R DS ( ON )( MAX ) =
Max ? V DS ? Sense ? Voltage
I O ? ρ T
MOSFET V DS voltage that appears between the PGND
and SW pins. The maximum allowed V DS sense voltage is
set by the voltage applied to the V RNG pin and is approxi-
mately equal to (0.133)V RNG . The current mode control
loop does not allow the inductor current valleys to exceed
(0.133)V RNG . In practice, one should allow margin, to ac-
count for variations in the LTC3879 and external component
values. A good guide for setting V RNG is:
V RNG = 7.5 ? (Maximum V DS Sense Voltage)
The ρ T term is a normalization factor (unity at 25°C)
accounting for the signi?cant variation in on-resistance
with temperature, typically about 0.4%/°C, as shown in
Figure 1. For a maximum junction temperature of 100°C
using a value of ρ T = 1.3 is reasonable.
The power dissipated by the top and bottom MOSFETs
depends upon their respective duty cycles and the load
current. When the LTC3879 is operating in continuous
mode, the duty cycles for the MOSFETs are:
An external resistive divider from INTV CC can be used
to set the voltage on the V RNG pin between 0.2V and 2V,
resulting in peak sense voltages between 26.6mV and
266mV. The wide peak voltage sense range allows for a
variety of applications and MOSFET choices. The V RNG pin
can also be tied to either SGND or INTV CC to force internal
defaults. When V RNG is tied to SGND, the device operates
at a valley current sense threshld of 30mV typical. If V RNG
is tied to INTV CC , the device operates at a valley current
sense threshold of 75mV typical.
Power MOSFET Selection
The LTC3879 requires two external N-channel power
MOSFETs, one for the top (main) switch and one for the
bottom (synchronous) switch. Important parameters for
D TOP =
D BOT =
V OUT
V IN
V IN – V OUT
V IN
2.0
1.5
1.0
0.5
the power MOSFETs are the breakdown voltage V BR(DSS) ,
threshold voltage V GS(TH) , on-resistance R DS(ON) , re-
0
–50
0
50
100
150
verse transfer capacitance C RSS and maximum current
I DS(MAX) .
JUNCTION TEMPERATURE (°C)
3879 F01
Figure 1. R DS(ON) vs Temperature
3879f
11
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| LTC3879IMSE#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) |
| LTC3879IMSE#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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| LTC3879IUD#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) |
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