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| 型号： | LM5051MAX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 16/23页 |
| 文件大小： | 0K |
| 描述： | IC ORING FET CTRLR 8SOIC |
| 标准包装： | 2,500 |
| 应用： | 冗余电源 |
| FET 型： | N 沟道 |
| 输出数： | 1 |
| 内部开关： | 无 |
| 电源电压： | 36 V ~ 100 V |
| 电流 - 电源： | 400µA |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOICN |
| 包装： | 带卷 (TR) |
SNVS702D – OCTOBER 2011 – REVISED MARCH 2013
The dominate MOSFET loss for the LM5051 active OR-ing controller is conduction loss due to source-to-drain
current to the output load, and the R DS(ON) of the MOSFET. This conduction loss could be reduced by using a
MOSFET with the lowest possible R DS(ON) . However, contrary to popular belief, arbitrarily selecting a MOSFET
based solely on having low R DS(ON) may not always give desirable results for several reasons:
1) Reverse transition detection. Higher R DS(ON) will provide increased voltage information to the LM5051 Reverse
Comparator at a lower reverse current level. This will give an earlier MOSFET turn-off condition should the input
voltage become shorted to ground. This will minimize any disturbance of the redundant bus.
2) Reverse current leakage. In cases where multiple input supplies are closely matched it may be possible for
some small current to flow continuously through the MOSFET drain to source (i.e. reverse) without activating the
LM5051 Reverse Comparator. Higher R DS(ON) will reduce this reverse current level.
3) Cost. Generally, as the R DS(ON) rating goes lower, the cost of the MOSFET goes higher.
Selecting a MOSFET with an R DS(ON) that is too large will result in excessive power dissipation.
As a guideline, it is suggest that R DS(ON) be selected to provide at least 20 mV, and no more than 100 mV, at the
nominal load current.
(20 mV / I D ) ≤ R DS(ON) ≤ (100mV / I D )
(10)
The thermal resistance of the MOSFET package should also be considered against the anticipated dissipation in
the MOSFET in order to ensure that the junction temperature (T J ) is reasonably well controlled, since the R DS(ON)
of the MOSFET increases as the junction temperature increases.
P DISS = I D2 x (R DS(ON) )
(11)
Operating with a maximum ambient temperature (T A(MAX) ) of 35°C, a load current of 10A, and an R DS(ON) of 10
m ? , and desiring to keep the junction temperature under 100°C, the maximum junction-to-ambient thermal
resistance rating ( θ JA ) would need to be:
θ JA ≤ (T J(MAX) - T A(MAX) )/(I D2 x R DS(ON) )
θ JA ≤ (100°C - 35°C)/(10A x 10A x 0.01 ? )
θ JA ≤ 65°C/W
(12)
(13)
(14)
16
Product Folder Links: LM5051
Copyright ? 2011–2013, Texas Instruments Incorporated
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