参数资料
型号: IR3651STRPBF
厂商: International Rectifier
文件页数: 14/19页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 14-SOIC
标准包装: 2,500
PWM 型: 电压模式
输出数: 1
频率 - 最大: 460kHz
占空比: 80%
电源电压: 4.5 V ~ 13.2 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: 0°C ~ 125°C
封装/外壳: 14-SOIC(0.154",3.90mm 宽)
包装: 带卷 (TR)
配用: IRDC3651-ND - KIT REF DESIGN SYNCH BUCK REG
IR3651SPBF
Power MOSFET Selection
The IR3651 uses two N-Channel MOSFETs. The
selections criteria to meet power transfer
requirements is based on maximum drain-source
voltage (V DSS ), gate-source drive voltage (V gs ),
maximum output current, On-resistance R DS(on)
and thermal management.
switching losses in synchronous Buck converter.
The synchronous MOSFET turns on under zero
voltage conditions, therefore, the turn on losses
for synchronous MOSFET can be neglected.
With a linear approximation, the total switching
loss can be expressed as:
V ds ( off ) t r + t f
The MOSFET must have a maximum operating
voltage (V DSS ) exceeding the maximum input
P sw =
2 T
*
* I load
- -(10)
voltage (V in ).
The gate drive requirement is almost the same
for both MOSFETs. Logic-level transistor can be
used and caution should be taken with devices at
very low V gs to prevent undesired turn-on of the
complementary MOSFET, which results in shoot-
through current.
The total power dissipation for MOSFETs
includes conduction and switching losses. For
the Buck converter the average inductor current
is equal to the DC load current. The conduction
loss is defined as:
Where:
V ds(off) = Drain to source voltage at the off time
t r = Rise time
t f = Fall time
T = Switching period
I load = Load current
The switching time waveforms is shown in
figure10.
V DS
P cond = (upper switch) = I
P cond = (lower switch) = I
2
load
2
load
? R ds(on) ? D ? ?
? R ds(on) ? (1 ? D) ? ?
90%
? = R ds(on) temperatur e dependency
The R DS(on) temperature dependency should be
considered for the worst case operation. This is
typically given in the MOSFET data sheet.
10%
V GS
Ensure that the conduction losses and switching
t d (ON)
t r
t d (OFF)
t f
losses do not exceed the package ratings or
violate the overall thermal budget.
The switching loss is more difficult to calculate,
even though the switching transition is well
understood. The reason is the effect of the
parasitic components and switching times during
the switching procedures such as turn-on / turn-
off delays and rise and fall times. The control
MOSFET contributes to the majority of the
06/08/2011
Fig. 10: switching time waveforms
14
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