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| 型号： | LTC3890MPUH#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 19/40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： | 2 |
| 频率 - 最大： | 850kHz |
| 占空比： | 99% |
| 电源电压： | 4 V ~ 60 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： | -55°C ~ 150°C |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3890
APPLICATIONS INFORMATION
I MAX ?
? ( V OUT ) ( V IN – V OUT ) ??
C IN Required I RMS ≈
V IN
? V OUT ≈ ? I L ? ESR + ?
V OUT = 0.8V ? 1 + B ?
RMS capacitor current requirement. Increasing the out-
put current drawn from the other controller will actually
decrease the input RMS ripple current from its maximum
value. The out-of-phase technique typically reduces the
input capacitor’s RMS ripple current by a factor of 30%
to 70% when compared to a single phase power supply
solution.
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle (V OUT )/(V IN ). To prevent
large voltage transients, a low ESR capacitor sized for the
maximum RMS current of one channel must be used. The
maximum RMS capacitor current is given by:
1/ 2
(1)
This formula has a maximum at V IN = 2V OUT , where I RMS
= I OUT /2. This simple worst-case condition is commonly
used for design because even significant deviations do not
offer much relief. Note that capacitor manufacturers’ ripple
current ratings are often based on only 2000 hours of life.
This makes it advisable to further derate the capacitor, or
to choose a capacitor rated at a higher temperature than
required. Several capacitors may be paralleled to meet
size or height requirements in the design. Due to the high
operating frequency of the LTC3890, ceramic capacitors
can also be used for C IN . Always consult the manufacturer
if there is any question.
The benefit of the LTC3890 2-phase operation can be cal-
culated by using Equation 1 for the higher power controller
and then calculating the loss that would have resulted if
both controller channels switched on at the same time.
The total RMS power lost is lower when both controllers
are operating due to the reduced overlap of current pulses
required through the input capacitor’s ESR. This is why
the input capacitor’s requirement calculated above for the
worst-case controller is adequate for the dual controller
design. Also, the input protection fuse resistance, battery
resistance, and PC board trace resistance losses are also
reduced due to the reduced peak currents in a 2-phase
system. The overall benefit of a multiphase design will
only be fully realized when the source impedance of the
power supply/battery is included in the efficiency testing.
The drains of the top MOSFETs should be placed within
1cm of each other and share a common C IN (s). Separating
the drains and C IN may produce undesirable voltage and
current resonances at V IN .
A small (0.1μF to 1μF) bypass capacitor between the chip
V IN pin and ground, placed close to the LTC3890, is also
suggested. A 10Ω resistor placed between C IN (C1) and
the V IN pin provides further isolation between the two
channels.
The selection of C OUT is driven by the effective series
resistance (ESR). Typically, once the ESR requirement
is satisfied, the capacitance is adequate for filtering. The
output ripple ( ? V OUT ) is approximated by:
? 1 ?
? 8 ? f ? C OUT ?
where f is the operating frequency, C OUT is the output
capacitance and ? I L is the ripple current in the inductor.
The output ripple is highest at maximum input voltage
since ? I L increases with input voltage.
Setting Output Voltage
The LTC3890 output voltages are each set by an external
feedback resistor divider carefully placed across the out-
put, as shown in Figure 5. The regulated output voltage
is determined by:
? R ?
? R A ?
To improve the frequency response, a feedforward ca-
pacitor, C FF , may be used. Great care should be taken to
route the V FB line away from noise sources, such as the
inductor or the SW line.
V OUT
1/2 LTC3890 R B C FF
V FB
R A
3890 F05
Figure 5. Setting Output Voltage
3890fc
19
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| LTC3891EFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| LTC3891EFE#PBF | 制造商:Linear Technology 功能描述:IC DC-DC CONV 900kHz TSSOP20 |
| LTC3891EFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP 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) |
| LTC3891EUDC#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 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 |
| LTC3891EUDC#PBF | 制造商:Linear Technology 功能描述:IC DC-DC CONV 900kHz QFN20 |
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