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| 型号： | LTC3855IFE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 32/44页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 38-SSOP |
| 标准包装： | 50 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 850kHz |
| 占空比： | 95% |
| 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： | 38-TFSOP （0.173"，4.40mm 宽）裸露焊盘 |
| 包装： | 管件 |
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LTC3855
APPLICATIONS INFORMATION
V OUT ?
V OUT
f ? ? I L ( MAX ) ?
V IN ( MAX ) ?
V OUT ? V OUT ?
f ? L ?
V IN ( NOM ) ?
t ON(MIN) =
V OUT 1.2V
V IN(MAX) f
= = 150ns
R SENSE(EQUIV) =
? I L(NOM)
I LOAD(MAX) +
= 0.6V ? ? 1 + B ?
V OUT
Thisoccursaround50%dutycycleoneitherchanneldue
to the phasing of the internal clocks and may cause minor
duty cycle jitter.
Reduce V IN from its nominal level to verify operation
of the regulator in dropout. Check the operation of the
undervoltage lockout circuit by further lowering V IN while
monitoring the outputs to verify operation.
Investigate whether any problems exist only at higher out-
put currents or only at higher input voltages. If problems
coincide with high input voltages and low output currents,
look for capacitive coupling between the BOOST, SW, TG,
and possibly BG connections and the sensitive voltage
and current pins. The capacitor placed across the current
sensing pins needs to be placed immediately adjacent to
the pins of the IC. This capacitor helps to minimize the
effects of differential noise injection due to high frequency
capacitive coupling. If problems are encountered with
high current output loading at lower input voltages, look
for inductive coupling between C IN , Schottky and the top
MOSFET components to the sensitive current and voltage
sensing traces. In addition, investigate common ground
path voltage pickup between these components and the
SGND pin of the IC.
Design Example
As a design example for a two channel high current regula-
tor, assume V IN = 12V(nominal), V IN = 20V(maximum),
V OUT1 = 1.8V, V OUT2 = 1.2V, I MAX1,2 = 15A, and f = 400kHz
(see Figure 16).
The regulated output voltages are determined by:
? R ?
? R A ?
Using 20k 1% resistors from both V FB nodes to ground,
the top feedback resistors are (to the nearest 1% standard
value) 40.2k and 20k.
input voltage:
?
L = ? 1 ? ?
Channel 1 will require 0.78μH, and channel 2 will require
0.54μH. The Vishay IHLP4040DZ-01, 0.56μH inductor is
chosen for both rails. At the nominal input voltage (12V),
the ripple current will be:
? I L ( NOM ) = ? 1 ? ?
Channel 1 will have 6.8A (46%) ripple, and channel 2 will
have 4.8A (32%) ripple. The peak inductor current will be
the maximum DC value plus one-half the ripple current,
or 18.4A for channel 1 and 17.4A for channel 2.
The minimum on-time occurs on channel 2 at the maximum
V IN , and should not be less than 90ns:
20V(400kHz)
With I LIM floating, the equivalent R SENSE resistor value
can be calculated by using the minimum value for the
maximum current sense threshold (45mV).
V SENSE(MIN)
2
The equivalent required R SENSE value is 2.4m? for chan-
nel 1 and 2.6m? for channel 2. The DCR of the 0.56μH
inductor is 1.7m? typical and 1.8m? maximum for a
25°C ambient. At 100°C, the estimated maximum DCR
value is 2.3m?. The maximum DCR value is just slightly
under the equivalent R SENSE values. Therefore, R2 is not
required to divide down the signal.
R1 =
=
ThefrequencyissetbybiasingtheFREQpinto1V(see
Figure 12).
The inductance values are based on a 35% maximum
ripple current assumption (5.25A for each channel). The
highest value of ripple current occurs at the maximum
For each channel, 0.1μF is selected for C1.
L 0.56 μ H
(DCR MAX at 25 ° C) ? C1 1.8m ? ? 0.1 μ F
Choose R1 = 3.09k
= 3.11k
3855f
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3855IUJ#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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 |
| LTC3855IUJ#PBF-ES | 制造商:Linear Technology 功能描述: |
| LTC3855IUJ#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 40-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) |
| LTC3856EFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 38TFSOP 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:2,000 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) |
| LTC3856EFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 38TSSOP 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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