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参数资料
| 型号： | LT3740EDHC |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 0.14 A SWITCHING CONTROLLER, 330 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 5 X 3 MM, PLASTIC, MO-229WJED-1, DFN-16 |
| 文件页数： | 4/20页 |
| 文件大小： | 234K |
| 代理商： | LT3740EDHC |
LT3740
12
3740fc
APPLICATIONS INFORMATION
Current Limit
The maximum inductor current is inherently limited in a
current mode controller by the maximum sense voltage.
In the LT3740, the maximum sense voltage is selected by
the RANGE pin. With valley current control, the maximum
sense voltage and the sense resistance determine the maxi-
mum allowed inductor valley current. The corresponding
output current limit is:
I
LIMIT =
V
SN(MAX)
R
S
+
ΔI
L
2
The current limit value should be checked to ensure that
ILIMIT(MIN) > IOUT(MAX). The maximum sense voltage in-
creases as duty cycle decreases. If MOSFET on-resistance
is used for current sensing, it is important to check for
self-consistency between the assumed MOSFET junction
temperature and the resulting value of ILIMIT which heats
the MOSFET switches.
In the event of output short-circuit to ground, the LT3740
operates at maximum inductor current and minimum duty
cycle. The actual inductor discharging voltage is the voltage
drop on the parasitic resistors including bottom MOSFET
on-resistance, inductor ESR, external sensing resistor if it
is used and the actual short-circuit load resistance. Because
of the big variation of these parasitic resistances, the top
MOSFET on-time can vary considerably for the same input
voltage. In the case of high input voltage and low parasitic
resistance, pulse-skipping may happen.
Efciency Considerations
The percent efciency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efciency and which change would
produce the most improvement. Although all dissipative
elements in the circuit produce losses, four main sources
account for most of the losses in LT3740 circuits:
1. DC I2R losses. These arise from the on-resistances of
the MOSFETs, external sensing resistor, inductor and
PC board traces and cause the efciency to drop at high
outputcurrents.Theaverageoutputcurrentowsthrough
the inductor, but is chopped between the top and bottom
MOSFETs. If the two MOSFETs have approximately the
same RDS(ON), then the resistance of one MOSFET can
simply be summed with the resistances of L and the board
traces to obtain the DC I2R loss. For example, if RDS(ON) =
0.01Ω and RL = 0.005Ω, the loss will range from 15mW
to 1.5W as the output current varies from 1A to 10A.
2. Transition loss. This loss arises from the brief amount
of time the top MOSFET spends in the saturated region
during switch node transitions. It depends upon the
input voltage, load current, driver strength and MOSFET
capacitance, among other factors. The loss is signicant
at high input voltages and can be estimated from:
Transition Loss = (1.7A–1) VIN2 IOUT CRSS FS
3. Gate drive loss. The previous formula show the factors
of this loss. For the top MOSFET, nothing can be done
other than choosing a small CGS MOSFET without
sacricing on-resistance. For the bottom MOSFET,
the gate drive loss can be reduced by choose the right
BGDP voltage supply.
4. CINloss.Theinputcapacitorhasthedifcultjobofltering
the large RMS input current to the regulator. It must have
a very low ESR to minimize the AC I2R loss and sufcient
capacitance to prevent the RMS current from causing
additional upstream losses in fuses or batteries.
Other losses, including COUT ESR loss, Schottky diode D1
conduction loss during dead time and inductor core loss
generally account for less than 2% additional loss.
When making adjustments to improve efciency, the input
current is the best indicator of changes in efciency. If a
change is made and the input current decreases, then the
efciency has increased. If there is no change in input
current, then there is no change in efciency.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3740EDHC#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-DFN 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 |
| LT3740EDHC#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-DFN 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) |
| LT3740EDHC-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Wide Operating Range, Valley Mode, No RSENSE? Synchronous Step-Down Controller |
| LT3740EDHC-TR | 制造商:LINER 制造商全称:Linear Technology 功能描述:Wide Operating Range, Valley Mode, No RSENSE? Synchronous Step-Down Controller |
| LT3740EDHC-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Wide Operating Range, Valley Mode, No RSENSE? Synchronous Step-Down Controller |
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