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| 型号： | LT3844EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST INV PWM 16TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 330kHz |
| 占空比： | 95% |
| 电源电压： | 4 V ~ 60 V |
| 降压： | 是 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 是 |
| 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： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 带卷 (TR) |
LT3844
APPLICATIONS INFORMATION
L > V OUT ?
2 DC MAX – 1 R SENSE ? 8 . 33
P COND OUT ( MAX ) ) ? OUT ? ( R DS ( ON ) )
= ( I
The typical range of values for ΔI L is (0.2 ? I OUT(MAX) ) to
(0.5 ? I OUT(MAX) ), where I OUT(MAX) is the maximum load
current of the supply. Using Δ I L = 0.3 ? I OUT(MAX) yields a
good design compromise between inductor performance
versus inductor size and cost. A value of Δ I L = 0.3 ? I OUT(MAX)
produces a ±15% of I OUT(MAX) ripple current around the DC
output current of the supply. Lower values of Δ I L require
larger and more costly magnetics. Higher values of Δ I L
will increase the peak currents, requiring more ?ltering
on the input and output of the supply. If Δ I L is too high,
the slope compensation circuit is ineffective and current
mode instability may occur at duty cycles greater than
50%. To satisfy slope compensation requirements the
minimum inductance is calculated as follows:
?
DC MAX f SW
Some magnetics vendors specify a volt-second product
in their data sheet. If they do not, consult the magnetics
vendor to make sure the speci?cation is not being exceeded
by your design. The volt-second product is calculated as
follows:
For more detailed information on selecting an inductor,
please see the “Inductor Selection” section of Linear
Technology Application Note 44.
Step-Down Converter: MOSFET Selection
The selection criteria of the external N-channel standard
level power MOSFET include on resistance(R DS(ON) ), re-
verse transfer capacitance (C RSS ), maximum drain source
voltage (V DSS ), total gate charge (Q G ) and maximum
continuous drain current.
For maximum ef?ciency, minimize R DS(ON) and C RSS .
Low R DS(ON) minimizes conduction losses while low C RSS
minimizes transition losses. The problem is that R DS(ON) is
inversely related to C RSS . Balancing the transition losses
with the conduction losses is a good idea in sizing the
MOSFET. Select the MOSFET to balance the two losses.
Calculate the maximum conduction losses of the
MOSFET:
2 ? V ?
? V IN ?
( V IN ( MAX ) – V OUT OUT
Volt-second (μsec) =
)? V
V INN ( MAX ) ? f SW
Note that R DS(ON) has a large positive temperature depen-
dence. The MOSFET manufacturer’s data sheet contains a
curve, R DS(ON) vs Temperature.
The magnetics vendors specify either the saturation cur-
rent, the RMS current or both. When selecting an inductor
based on inductor saturation current, use the peak cur-
rent through the inductor, I OUT(MAX) + Δ I L /2. The inductor
saturation current speci?cation is the current at which
the inductance, measured at zero current, decreases by
a speci?ed amount, typically 30%.
When selecting an inductor based on RMS current rating,
use the average current through the inductor, I OUT(MAX) .
The RMS current speci?cation is the RMS current at which
the part has a speci?c temperature rise, typically 40°C,
above 25°C ambient.
After calculating the minimum inductance value, the
volt-second product, the saturation current and the RMS
current for your design, select an off-the-shelf inductor.
Contact the Application group at Linear Technology for
further support.
Calculate the maximum transition losses:
P TRAN = (k)(V IN ) 2 (I OUT(MAX) )(C RSS )(f SW )
where k is a constant inversely related to the gate driver
current, approximated by k = 2 for LT3844 applications.
The total maximum power dissipation of the MOSFET is
the sum of these two loss terms:
P FET(TOTAL) = P COND + P TRAN
To achieve high supply ef?ciency, keep the P FET(TOTAL) to
less than 3% of the total output power. Also, complete
a thermal analysis to ensure that the MOSFET junction
temperature is not exceeded.
T J = T A + P FET(TOTAL) ? θ JA
where θ JA is the package thermal resistance and T A is the
ambient temperature. Keep the calculated T J below the max-
imum speci?ed junction temperature, typically 150°C.
3844fb
12
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相关代理商/技术参数 |
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| LT3844IFE | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 4V to 60V Input 16-Pin TSSOP EP |
| LT3844IFE#PBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP 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) |
| LT3844IFE#TRPBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP 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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| LT3844IFE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Voltage, Current Mode Switching Regulator Controller with Programmable Operating Frequency |
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