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参数资料
| 型号： | LTC3733CUHF-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/32页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR BUCK 3PH AMD CPU 38-QFN |
| 标准包装： | 2,500 |
| 应用： | 控制器，AMD |
| 输入电压： | 4 V ~ 36 V |
| 输出数： | 1 |
| 输出电压： | 0.8 V ~ 1.55 V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 38-WFQFN 裸露焊盘 |
| 供应商设备封装： | 38-QFN（5x7） |
| 包装： | 带卷 (TR) |
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LTC3733/LTC3733-1
APPLICATIO S I FOR ATIO
So the number of phases used can be selected to minimize
the output ripple current and therefore the output ripple
voltage at the given input and output voltages. In applica-
tions having a highly varying input voltage, additional
phases will produce the best results.
Accepting larger values of ? I L allows the use of low
inductances but can result in higher output voltage ripple.
A reasonable starting point for setting ripple current is
? I L = 0.4(I OUT )/N, where N is the number of channels and
I OUT is the total load current. Remember, the maximum
? I L occurs at the maximum input voltage. The individual
inductor ripple currents are constant determined by the
inductor, input and output voltages.
Ferrite designs have very low core loss and are preferred
at high switching frequencies, so design goals can
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard,” which means that
inductance collapses abruptly when the peak design
current is exceeded. This results in an abrupt increase in
inductor ripple current and consequent output voltage
ripple. Do not allow the core to saturate!
Power MOSFET and D1, D2, D3 Selection
At least two external power MOSFETs must be selected for
each of the three output sections: One N-channel MOSFET
for the top (main) switch and one or more N-channel
MOSFET(s) for the bottom (synchronous) switch. The
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
number, type and “on” resistance of all MOSFETs selected
take into account the voltage step-down ratio as well as the
actual position (main or synchronous) in which the MOSFET
will be used. A much smaller and much lower input
capacitance MOSFET should be used for the top MOSFET
in applications that have an output voltage that is less than
1/3 of the input voltage. In applications where V IN >> V OUT ,
the top MOSFETs’ “on” resistance is normally less impor-
tant for overall efficiency than its input capacitance at
0.1
0
0.1
0.2
0.3 0.4
0.5 0.6 0.7
0.8
0.9
operating frequencies above 300kHz. MOSFET manufac-
turers have designed special purpose devices that provide
DUTY FACTOR (V OUT /V IN )
3733 F04
Figure 4. Normalized Peak Output Current
vs Duty Factor [I RMS = 0.3(I O(P-P) ]
Inductor Core Selection
Once the value for L1 to L3 is known, the type of inductor
must be selected. High efficiency converters generally
cannot afford the core loss found in low cost powdered
iron cores, forcing the use of ferrite, molypermalloy or
Kool M μ ? cores. Actual core loss is independent of core
size for a fixed inductor value, but it is very dependent on
inductance selected. As inductance increases, core losses
go down. Unfortunately, increased inductance requires
more turns of wire and therefore copper losses will
increase.
reasonably low “on” resistance with significantly reduced
input capacitance for the main switch application in switch-
ing regulators.
The peak-to-peak MOSFET gate drive levels are set by the
voltage, V CC , requiring the use of logic-level threshold
MOSFETs in most applications. Pay close attention to the
BV DSS specification for the MOSFETs as well; many of the
logic-level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFETs include the “on”
resistance R SD(ON) , input capacitance, input voltage and
maximum output current.
MOSFET input capacitance is a combination of several
components but can be taken from the typical “gate
charge” curve included on most data sheets (Figure 5).
The curve is generated by forcing a constant input current
Kool M μ is a registered trademark of Magnetics, Inc.
3733f
14
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PDF描述 |
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| HSM22DSAN | CONN EDGECARD 44POS R/A .156 SLD |
| HMM22DSAN | CONN EDGECARD 44POS R/A .156 SLD |
| LTC3733CUHF-1#TR | IC CTRLR BUCK 3PH AMD CPU 38-QFN |
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| HSM22DSAH | CONN EDGECARD 44POS R/A .156 SLD |
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