参数资料
型号: LM5051MAX/NOPB
厂商: National Semiconductor
文件页数: 13/23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:
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
Several factors can prevent the nFGD pin from indicating that the external MOSFET is operating normally. If the
LM5051 is used to connect parallel, redundant power supplies, one of the connected supplies may hold the
INP/VSS pin voltage close enough to the LM5051 INN pin voltage that the V SD(TST) threshold is not exceeded.
Additionally, operating with a high output capacitance value and low output load current may require a significant
amount of time before the output load capacitance is discharged to the point where the V SD(TST) threshold is
crossed and the nFGD pin switches.
The status of the nFGD pin does not depend on the status of the OFF pin. The status of the nFGD pin depends
only on the voltage at the INN pin relative to the INP/VSS pin being above, or below, the V SD(TST) threshold
voltage.
The nFGD output pin requires pull-up to an external voltage source, and must not be pulled higher than 5.5V
above the INP/VSS pin. It is recommended that the nFGD pin is not required to sink more than 2mA.
VCC PIN
The VCC pin is connected to the cathode of the internal shunt (zener) voltage regulator. The anode of the shunt
regulator is connected to the INP/VSS pin. The VCC pin provides bias for internal circuitry, as well as gate drive
to the external MOSFET. The VCC pin should always be bypassed with a 0.1 μ F ceramic capacitor to the
INP/VSS pin.
Typically, the VCC pin is biased from the LINE pin, through the internal 50 k ? series resistor, when the available
V LINE voltage is not less than the 36V minimum operating voltage.
If the available LINE voltage is less than less than the 36V minimum operating voltage the VCC pin can be
biased through the use of an external resistor to an appropriate bias supply that is referenced to the INP/VSS
pin.
A minimum VCC pin bias current of 1 mA is recommended, with a recommended 10 mA maximum.
A design example for calculating the external resistor where the VCC pin will be biased from an 18V to 36V
supply (relative to the INP/VSS pin):
R BIAS = (V BIAS(MIN) - V Z ) / I BIAS(MIN)
R BIAS = (18V - 13V) / 1 mA
R BIAS = 5.0 k ?
(1)
(2)
(3)
Next, using the calculated R BIAS resistor value, verify that the VCC pin current will be no more than 10mA at the
maximum V BIAS voltage:
ICC = (V BIAS(MAX) - 13V) / R BIAS
ICC = (36V - 13V) / 5.0 k ?
ICC = 4.6 mA
Since the calculated 4.6 mA is less than the 10 mA maximum, the 5 k ? value for R BIAS is acceptable.
R BIAS
(4)
(5)
(6)
LINE
LM5051
VCC
INN
GATE INP/VSS
0.1 F
Figure 29. Using an External Resistor to Bias the VCC Pin
Copyright ? 2011–2013, Texas Instruments Incorporated
Product Folder Links: LM5051
13
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