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参数资料
| 型号： | LT3741IFE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 1070 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封装： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-20 |
| 文件页数： | 6/24页 |
| 文件大小： | 243K |
| 代理商： | LT3741IFE#TRPBF |
LT3741
14
3741fb
(RDS(ON)), gate to drain charge (QGD), gate-to-source
charge (QGS), gate resistance (RG), breakdown voltages
(maximum VGS and VDS) and drain current (maximum ID).
The following guidelines provide information to make the
selection process easier.
Both of the switching MOSFETs need to have their maximum
rateddraincurrentsgreaterthanthemaximuminductorcurrent.
The following equation calculates the peak inductor current:
I
MAX = IO +
V
IN VO –VO
2
2 f
S L VIN
where VIN is the input voltage, L is the inductance value, VO
is the output voltage, IO is the regulated output current and fS
is the switching frequency. During MOSFET selection, notice
that the maximum drain current is temperature dependant.
Most data sheets include a table or graph of the maximum
rated drain current vs temperature.
The maximum VDS should be selected to be higher than the
maximum input supply voltage (including transient) for both
MOSFETs. The signals driving the gates of the switching
MOSFETs have a maximum voltage of 5V with respect to the
source.Duringstart-upandrecoveryconditions,thegatedrive
signalsmaybeaslowas3V.ToensurethattheLT3741recovers
properly, the maximum threshold should be less than 2V. For
a robust design, select the maximum VGS greater than 7V.
Power losses in the switching MOSFETs are related to the
on-resistance, RDS(ON);thetransitionallossrelatedtothegate
resistance, RG; gate-to-drain capacitance, QGD and gate-to-
sourcecapacitance,QGS.Powerlosstotheon-resistanceisan
Ohmicloss,I2RDS(ON),andusuallydominatesforinputvoltages
lessthan~15V.Powerlossestothegatecapacitancedominate
for voltages greater than ~12V. When operating at higher input
voltages, efciency can be optimized by selecting a high side
MOSFET with higher RDS(ON) and lower CGD. The power loss
in the high side MOSFET can be approximated by:
PLOSS = (ohmic loss) + (transition loss)
P
LOSS ≈
V
O
()
V
IN
I
O
2 R
DS(ON) ρT
+
V
IN IOUT
5V
Q
GD + QGS
()2R
G + RPU + RPD
()
()f
S
where
rTisatemperature-dependanttermoftheMOSFET’s
on-resistance. Using 70°C as the maximum ambient operat-
ing temperature,
rT is roughly equal to 1.3. RPD and RPU
are the LT3741 high side gate driver output impedance,
1.3Ω and 2.3Ω respectively.
A good approach to MOSFET sizing is to select a high
side MOSFET, then select the low side MOSFET. The trade-
off between RDS(ON), QG, QGD and QGS for the high side
MOSFET is shown in the following example. VO is equal
to 4V. Comparing two N-channel MOSFETs, with a rated
VDS of 40V and in the same package, but with 8
different
RDS(ON) and 4.5
different QG and QGD:
M1: RDS(ON) = 2.3mΩ, QG = 45.5nC,
QGS = 13.8nC, QGD = 14.4nC, RG = 1Ω
M2: RDS(ON) = 18mΩ, QG = 10nC,
QGS = 4.5nC, QGD = 3.1nC, RG = 3.5Ω
Power loss for both MOSFETs is shown in Figure 4. Observe
that while the RDS(ON) of M1 is eight times lower, the power
loss at low input voltages is equal, but four times higher
at high input voltages than the power loss for M2.
Power loss within the low side MOSFET is almost entirely
from the RDS(ON) of the FET. Select a low side FET with
the lowest RDS(ON) while keeping the total gate charge QG
to 30nC or less.
Another power loss related to switching MOSFET selection
is the power lost to driving the gates. The total gate charge,
QG, must be charged and discharged each switching cycle.
The power is lost to the internal LDO within the LT3741.
The power lost to the charging of the gates is:
PLOSS_LDO ≈ (VIN – 5V) (QGLG + QGHG) fS
where QGLG is the low side gate charge and QGHG is the
high side gate charge.
Whenever possible, utilize a switching MOSFET that
minimizes the total gate charge to limit the internal power
dissipation of the LT3741.
APPLICATIONS INFORMATION
相关PDF资料 |
PDF描述 |
|---|---|
| LT3741EUF#PBF | SWITCHING CONTROLLER, 1070 kHz SWITCHING FREQ-MAX, PQCC20 |
| LT3741EUF#TRPBF | SWITCHING CONTROLLER, 1070 kHz SWITCHING FREQ-MAX, PQCC20 |
| LT3741IUF#PBF | SWITCHING CONTROLLER, 1070 kHz SWITCHING FREQ-MAX, PQCC20 |
| LT3748HMS#PBF | SWITCHING CONTROLLER, PDSO12 |
| LT3758HMSE#TRPBF | SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO10 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3741IUF#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:- 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 |
| LT3741IUF#PBF | 制造商:Linear Technology 功能描述:DC-DC CONTROLLER BUCK 1MHZ 制造商:Linear Technology 功能描述:DC-DC CONTROLLER, BUCK, 1MHZ, QFN-20 |
| LT3741IUF#TRPBF | 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:- 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 |
| LT3741IUF-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Power, Constant Current, Constant Voltage, Step-Down Controller |
| LT3741IUF-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Power, Constant Current, Constant Voltage, Step-Down Controller |
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