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参数资料
| 型号： | LT3724MPFE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 13/26页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST INV PWM 16TSSOP |
| 标准包装： | 95 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 225kHz |
| 占空比： | 100% |
| 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： | -55°C ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 管件 |
LT3724
APPLICATIONS INFORMATION
P COND = (I OUT(MAX) ) 2 ? OUT ? (R DS(ON) )
I DIODE(AVG) = I OUT(MAX)
For maximum efficiency, 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:
? V ?
? V IN ?
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.
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 LT3724 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 efficiency, 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
maximum specified junction temperature, typically 150°C.
Note that when V IN is high, the transition losses may
dominate. A MOSFET with higher R DS(ON) and lower C RSS
may provide higher efficiency. MOSFETs with higher volt-
age V DSS specification usually have higher R DS(ON) and
lower C RSS .
Choose the MOSFET V DSS specification to exceed the
maximum voltage across the drain to the source of the
MOSFET, which is V IN(MAX) plus any additional ringing
on the switch node. Ringing on the switch node can be
greatly reduced with good PCB layout and, if necessary,
an RC snubber.
The internal V CC regulator operating range limits the maxi-
mum total MOSFET gate charge, Q G , to 90nC. The Q G vs
V GS specification is typically provided in the MOSFET data
sheet. Use Q G at V GS of 8V. If V CC is back driven from an
external supply, the MOSFET drive current is not sourced
from the internal regulator of the LT3724 and the Q G of the
MOSFET is not limited by the IC. However, note that the
MOSFET drive current is supplied by the internal regulator
when the external supply back driving V CC is not available
such as during startup or short-circuit.
The manufacturer’s maximum continuous drain current
specification should exceed the peak switch current,
I OUT(MAX) + ?I L /2.
During the supply startup, the gate drive levels are set by
the V CC voltage regulator, which is approximately 8V. Once
the supply is up and running, the V CC can be back driven
by an auxiliary supply such as V OUT . It is important not to
exceed the manufacturer’s maximum V GS specification.
A standard level threshold MOSFET typically has a V GS
maximum of 20V.
Step-Down Converter: Rectifier Selection
The rectifier diode (D1 on the Functional Diagram) in a
buck converter generates a current path for the inductor
current when the main power switch is turned off. The
rectifier is selected based upon the forward voltage, re-
verse voltage and maximum current. A Schottky diode is
recommended. Its low forward voltage yields the lowest
power loss and highest efficiency. The maximum reverse
voltage that the diode will see is V IN(MAX) .
In continuous mode operation, the average diode cur-
rent is calculated at maximum output load current and
maximum V IN :
V IN(MAX) ? V OUT
V IN(MAX)
To improve efficiency and to provide adequate margin for
short-circuit operation, a diode rated at 1.5 to 2 times the
maximum average diode current, I DIODE(AVG) , is recom-
mended.
3724fd
13
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相关代理商/技术参数 |
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| LT3724MPFE-TR | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Voltage, Current Mode Switching Regulator Controller |
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