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参数资料
| 型号： | LTC3708EUH#TR |
| 厂商： | Linear Technology |
| 文件页数： | 16/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 32-QFN |
| 标准包装： | 2,500 |
| 系列： | PolyPhase® |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 占空比： | 90% |
| 电源电压： | 4 V ~ 36 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： | 32-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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LTC3708
APPLICATIONS INFORMATION
highest (V OUT )(I OUT ) product needs to be used in the
formula below to determine the maximum RMS current
requirement. Increasing the output current, drawn from
the other out-of-phase controller, will actually decrease
the input RMS ripple current from this maximum value
(see Figure 2).
The type of input capacitor, value and ESR rating have ef-
?ciency effects that need to be considered in the selection
process. The capacitance value chosen should be suf?cient
to store adequate charge to keep pulsating input currents
down. 20μF to 40μF is usually suf?cient for a 25W output
supply operating at 200kHz. The ESR of the capacitor
is important for capacitor power dissipation as well as
overall ef?ciency. All of the power (RMS ripple current 2
? ESR) not only heats up the capacitor but wastes power
from the battery.
Medium voltage (20V to 35V) ceramic, tantalum, OS-CON
and switcher-rated electrolytic capacitors can be used
as input capacitors, but each has drawbacks: ceramic
voltage coef?cients are very high and may have audible
piezoelectric effects; tantalums need to be surge-rated;
OS-CONs suffer from higher inductance, larger case
size and limited surface-mount applicability; electrolyt-
ics’ higher ESR and dryout possibility require several to
be used. 2-phase systems allow the lowest amount of
capacitance overall. As little as one 22μF or two to three
10μF ceramic capacitors are an ideal choice in a 20W to
35W power supply due to their extremely low ESR. Even
though the capacitance at 20V is substantially below their
rating at zero-bias, very low ESR loss makes ceramics
an ideal candidate for highest ef?ciency battery operated
systems. Also consider parallel ceramic and high quality
electrolytic capacitors as an effective means of achieving
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 signi?cant deviations do not
offer much relief. Note that capacitor manufacturer’s 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 also be paralleled to meet
size or height requirements in the design. Always consult
the manufacturer if there is any question.
The bene?t of the LTC3708 2-phase operation can be
calculated by using the equation above for the higher
power channel and then calculating the loss that would
have resulted if both controller channels switch on at the
same time. The total RMS power lost is lower when both
controllers are operating due to the interleaving of current
pulses 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. Remember that 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 bene?t of a 2-phase design
will only be fully realized when the source impedance of
the power supply/battery is included in the ef?ciency
testing. The drains of the two 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 un-
desirable voltage and current resonances at V IN .
The selection of C OUT is driven by the effective series
resistance (ESR) required to minimize voltage ripple
and load step transients. The output ripple ( Δ V OUT ) is
determined by:
Δ V OUT L ? ESR +
≈ Δ I
8 fC OUT ?
ESR and bulk capacitance goals.
In continuous mode, the current of the top N-channel
MOSFET is approximately a square wave of duty cycle
?
?
1 ?
?
V OUT /V IN . To prevent large voltage transients, a low ESR
input capacitor sized for the maximum RMS current of
one channel must be used. The maximum RMS capacitor
current is given by:
where f = operating frequency, C OUT = output capacitance,
and Δ I L = ripple current in the inductor. The output ripple
is highest at maximum input voltage since Δ I L increases
with input voltage. Typically, once the ESR requirement
( )
? V OUT IN OUT ?
V ? V
I RMS ≈ I MAX
? ?
V IN
1 / 2
is satis?ed, the capacitance is adequate for ?ltering and
has the necessary RMS current rating.
3708fb
16
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相关代理商/技术参数 |
参数描述 |
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| LTC3709EG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-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:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3709EG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-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:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3709EUH | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Sync Step Down 5V to 36V Input 32-Pin QFN EP |
| LTC3709EUH#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:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3709EUH#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:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 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:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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