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参数资料
| 型号： | LTC3788IGN-1#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-28 |
| 文件页数： | 9/30页 |
| 文件大小： | 384K |
| 代理商： | LTC3788IGN-1#PBF |
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LTC3788-1
17
37881fb
applicaTions inForMaTion
The MOSFET power dissipations at maximum output
current are given by:
PMAIN =
(VOUT VIN)VOUT
V 2
IN
IOUT(MAX)
2 1+ d
(
)
RDS(ON) + k V
3
OUT
IOUT(MAX)
VIN
RDR
CMILLER f
PSYNC =
VIN
VOUT
IOUT(MAX)
2 1+ d
(
)RDS(ON)
where
d is the temperature dependency of RDS(ON) and
RDR (approximately 1Ω) is the effective driver resistance
at the MOSFET’s Miller threshold voltage. The constant k,
which accounts for the loss caused by reverse recovery
current, is inversely proportional to the gate drive current
and has an empirical value of 1.7.
BothMOSFETshaveI2RlosseswhilethebottomN-channel
equation includes an additional term for transition losses,
which are highest at low input voltages. For high VIN the
high current efficiency generally improves with larger
MOSFETs, while for low VIN the transition losses rapidly
increase to the point that the use of a higher RDS(ON)device
with lower CMILLERactuallyprovideshigherefficiency.The
synchronous MOSFET losses are greatest at high input
voltage when the bottom switch duty factor is low or dur-
ing overvoltage when the synchronous switch is on close
to 100% of the period.
The term (1+
d) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs Temperature curve, but
d = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
CIN and COUT Selection
The input ripple current in a boost converter is relatively
low(comparedwiththeoutputripplecurrent),becausethis
currentiscontinuous.TheinputcapacitorCINvoltagerating
should comfortably exceed the maximum input voltage.
Although ceramic capacitors can be relatively tolerant of
overvoltage conditions, aluminum electrolytic capacitors
are not. Be sure to characterize the input voltage for any
possible overvoltage transients that could apply excess
stress to the input capacitors.
The value of the CIN is a function of the source impedance,
andingeneral,thehigherthesourceimpedance,thehigher
the required input capacitance. The required amount of
input capacitance is also greatly affected by the duty cycle.
High output current applications that also experience high
duty cycles can place great demands on the input supply,
both in terms of DC current and ripple current.
Inaboostconverter,theoutputhasadiscontinuouscurrent,
so COUT must be capable of reducing the output voltage
ripple.TheeffectsofESR(equivalentseriesresistance)and
the bulk capacitance must be considered when choosing
the right capacitor for a given output ripple voltage. The
steady ripple voltage due to charging and discharging the
bulk capacitance is given by:
VRIPPLE =
IOUT(MAX) (VOUT VIN(MIN))
COUT VOUT f
V
where COUT is the output filter capacitor.
The steady ripple due to the voltage drop across the ESR
is given by:
VESR = IL(MAX) ESR
The LTC3788-1 can also be configured as a 2-phase single
output converter where the outputs of the two channels
are connected together and both channels have the same
duty cycle. With 2-phase operation, the two channels of
the dual switching regulator are operated 180 degrees
out-of-phase.Thiseffectivelyinterleavestheoutputcurrent
pulses,greatlyreducingtheoutputcapacitorripplecurrent.
As a result, the ESR requirement of the capacitor can be
relaxed. Because the ripple current in the output capacitor
is a square wave, the ripple current requirements for the
output capacitor depend on the duty cycle, the number
of phases and the maximum output current. Figure 3 il-
lustrates the normalized output capacitor ripple current
as a function of duty cycle in a 2-phase configuration. To
choose a ripple current rating for the output capacitor,
first establish the duty cycle range based on the output
voltage and range of input voltage. Referring to Figure 3,
choose the worst-case high normalized ripple current as
a percentage of the maximum load current.
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相关代理商/技术参数 |
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| LTC3788IUH#PBF | 功能描述:IC REG CTRLR BST 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:- 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 |
| LTC3788IUH#TRPBF | 功能描述:IC REG CTRLR BST 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:- 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 |
| LTC3789EGN#PBF | 功能描述:IC REG CTRLR BST 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:- 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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