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| 型号： | LTC3852IUDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/32页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR DOUBLER PWM 24-QFN |
| 标准包装： | 73 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 810kHz |
| 占空比： | 99% |
| 电源电压： | 2.7 V ~ 38 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 是 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 包装： | 管件 |
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LTC3852
APPLICATIONS INFORMATION
The peak-to-peak drive levels are set by the V PUMP voltage.
This voltage is typically 5V when the charge pump is active.
Consequently, logic-level threshold MOSFETs may be used
in most applications.
Selection criteria for the power MOSFETs include the on-
resistance, R DS(ON) , Miller capacitance, C MILLER , input
voltage and maximum output current. Miller capacitance,
C MILLER , can be approximated from the gate charge curve
usually provided on the MOSFET manufacturers’ data
sheet. C MILLER is equal to the increase in gate charge
along the horizontal axis while the curve is approximately
?at divided by the speci?ed change in V DS . This result is
then multiplied by the ratio of the application applied V DS
to the gate charge curve speci?ed V DS . When the IC is
operating in continuous mode, the duty cycles for the top
and bottom MOSFETs are given by:
the high current ef?ciency generally improves with larger
MOSFETs, while for V IN > 20V, the transition losses rapidly
increase to the point that the use of a higher R DS(ON) device
with lower C MILLER actually provides higher ef?ciency. The
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during
short-circuit 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 R DS(ON) vs Temperature curve, but
d = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
The optional Schottky diode conducts during the dead time
between the conduction of the two power MOSFETs. This
prevents the body diode of the bottom MOSFET from turning
on, storing charge during the dead time and requiring a
V OUT
Main Switch Duty Cycle =
V IN
Synchronous Switch Duty Cycle =
V IN – V OUT
V IN
reverse recovery period that could cost as much as 2%
in ef?ciency at high V IN . A 1A to 3A Schottky is generally
a good size due to the relatively small average current.
Larger diodes result in additional transition losses due to
their larger junction capacitance.
= OUT ( I MAX ) ( 1 + δ ) R DS(ON) +
( I MAX ) 2 ( 1 + δ ) R DS(ON)
P SYNC =
The MOSFET power dissipations at maximum output
current are given by:
V 2
P MAIN
V IN
?? 2 ??
( V IN ) 2 ? I MAX ? ( R DR ) ( C MILLER ) ?
? ?
? 1 1 ?
? + ? (f)
? V INTVCC – V TH(MIN) V TH(MIN) ?
V IN – V OUT
V IN
where d is the temperature dependency of R DS(ON) and
R DR (approximately 2 W ) is the effective driver resistance
at the MOSFET’s Miller threshold voltage. V TH(MIN) is the
typical MOSFET minimum threshold voltage.
Soft-Start and Tracking
The LTC3852 has the ability to either soft-start by itself
with a capacitor or track the output of another channel
or external supply. When the LTC3852 is con?gured to
soft-start by itself, a capacitor should be connected to
the TRACK/SS pin. The LTC3852 is in the shutdown state
if the RUN pin voltage is below 1.25V. TRACK/SS pin is
actively pulled to ground in this shutdown state.
Once the RUN pin voltage is above 1.25V, the LTC3852 powers
up. A soft-start current of 1μA then starts to charge its soft-
start capacitor. Note that soft-start or tracking is achieved
not by limiting the maximum output current of the controller
but by controlling the output ramp voltage according to the
ramp rate on the TRACK/SS pin. Current foldback is disabled
during this phase to ensure smooth soft-start or tracking. The
soft-start or tracking range is 0V to 0.8V on the TRACK/SS
pin. The total soft-start time can be calculated as:
Both MOSFETs have I 2 R losses while the topside N-channel
equation includes an additional term for transition losses,
which are highest at high input voltages. For V IN < 20V,
t SOFT-START = 0. 8 ?
C SS
1.0μA
3852f
17
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| LTC3853EUJ#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 |
| LTC3853EUJ#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® 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 |
| LTC3853EUJPBF | 制造商:Linear Technology 功能描述:DC-DC Controller Triple Buck 24V QFN40 |
| LTC3853IUJ#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® 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 |
| LTC3853IUJ#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: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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