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| 型号： | LTC3839EUH#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 35/50页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 32-QFN |
| 标准包装： | 73 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 2MHz |
| 电源电压： | 4.5 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： | 32-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3839
APPLICATIONS INFORMATION
V OUT = 0.6V ? ? 1 + FB2 ?
where Qg (TOP) and Qg (BOT) are the gate charges of the
top and bottom MOSFETs, respectively.
Supplying DRV CC power through EXTV CC could save
several percents of efficiency, especially for high V IN
applications. Connecting EXTV CC to an output-derived
source will scale the V IN current required for the driver
and controller circuits by a factor of (Duty Cycle)/
(Efficiency). For example, in a 20V to 5V application,
10mA of DRV CC current results in approximately 2.5mA
of V IN current. This reduces the mid-current loss from
10% or more (if the driver was powered directly from
V IN ) to only a few percent.
Design Example
Consider a 2-phase step-down converter from V IN =
4.5V to 26V to V OUT = 1.2V, with I OUT(MAX) = 30A, and
f = 350kHz (see Figure 13).
The regulated output voltage is determined by:
? R ?
? R FB1 ?
Using a 10k resistor for R FB1 , R FB2 is also 10k.
The frequency is programmed by:
4. C IN loss. The input capacitor filters large square-wave
input current drawn by the regulator into an averaged
R T [ k Ω ] =
41550
f [ kHz ]
– 2.2 =
41550
350
– 2.2 ≈ 116.5
DC current from the supply. The capacitor itself has
a zero average DC current, but square-wave-like AC
current flows through it. Therefore the input capacitor
must have a very low ESR to minimize the RMS current
loss on ESR. It must also have sufficient capacitance
to filter out the AC component of the input current to
prevent additional RMS losses in upstream cabling,
fuses or batteries. The LTC3839’s PolyPhase architecture
improves the ESR loss.
“Hidden” copper trace, fuse and battery resistance, even
Use the nearest 1% resistor standard value of 115k.
The minimum on-time occurs for maximum V IN . Using the
t ON(MIN) curves in the Typical Performance Characteristics
as references, make sure that the t ON(MIN) at maximum V IN
is greater than that the LTC3839 can achieve, and allow
sufficient margin to account for the extension of effective
on-time at light load due to the dead times (t D(TG/BG) +
t D(TG/BG) in the Electrical Characteristics). The minimum
on-time for this application is:
at DC current, can cause a significant amount of efficiency
degradation, so it is important to consider them during
the design phase. Other losses, which include the C OUT
t ON(MIN) =
V OUT
V IN(MAX) ? f
=
1.2V
24V ? 350kHz
= 143ns
ESR loss, bottom MOSFET ’s body diode reverse-recovery
loss, and inductor core loss generally account for less
than 2% additional loss.
Set the inductor value to give 40% ripple current of a single
phase (30A/2 = 15A) at maximum V IN using the adjusted
operating frequency:
L = ?
? ? ? ? 1– 24V ? ? = 0.54μH
Power losses in the switching regulator will reflect as
a higher than ideal duty cycle, or a longer on-time for a
constant frequency. This efficiency accounted on-time
? 1.2V
? 350kHz ? 40% ? 15A
? ? 1.2V ?
can be calculated as:
t ON ≈ t ON(IDEAL) /Efficiency
Select 0.56μH which is the nearest standard value.
The resulting maximum ripple current is:
Δ I L = ?
? ? ? ? 1– 24V ? ? = 5.8A
Whenmakingadjustmentstoimproveefficiency,theinput
current is the best indicator of changes in efficiency. If you
make a change and the input current decreases, then the
? 1.2V
? 350kHz ? 0.56μH
? ? 1.2V ?
efficiency has increased.
3839fa
35
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| LTC3839IUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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) |
| LTC3839IUH#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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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| LTC3850EGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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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