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PI2001 Datasheet(PDF) 17 Page - Vicor Corporation |
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PI2001 Datasheet(HTML) 17 Page - Vicor Corporation |
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17 / 23 page ![]() Typical application Example 2: Requirement: Redundant Bus Voltage = 12V (±10%, 10.8V to 13.2V) Load Current = 10A (assume through each redundant path) Maximum Ambient Temperature = 75°C Auxiliary Voltage = 24V±10% (21.6V to 26.4V) referenced to GND Solution: 1. A single PI2001 with suitable external MOSFET for each redundant 12V power source should be used, configured in a high-side floating configuration as shown in the circuit schematic in Figure 16. The controller is floated on Vin by connecting the controller ground pin to the input voltage Vin. 2. Select a suitable N-Channel MOSFET: Select an N-Channel MOSFET with a voltage rating higher than the 12V input plus any expected transient voltages, with a low Rds(on) that is capable of supporting full load current with margin. For instance, a 30V rated MOSFET with 20A current capability is suitable. An exemplary MOSFET having these characteristic is FDS8812NZ from Fairchild. From FDS8812NZ datasheet: • N-Channel MOSFET • VDS= 30V • ID = 20A continuous drain current • VGS(MAX)= ± 20V • RθJA= 50°C/W • RDS(on)=3.2mΩ typical at ID=10A, VGS=8V, TJ=25°C Reverse current threshold is: A m mV on Rds reverse Vth reverse Is 87 . 1 2 . 3 6 ) ( . . − = Ω − = = Power dissipation: Rds(on) is 4.2mΩ maximum at 25°C & 8Vgs and will increase as the temperature increases. Add 25°C to maximum ambient temperature to compensate for the temperature rise due to power dissipation. At 100°C (75°C + 25°C) Rds(on) will increase by 28%. Ω = ∗ Ω = m m on Rds 37 . 5 28 . 1 2 . 4 ) ( maximum at 100°C ) ( 2 on Rds Is Rth Trise JA ∗ ∗ = Maximum Junction temperature Trise T T A J + = max C m A W C C T J ° = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ Ω ∗ ∗ ° + ° = 102 37 . 5 ) 10 ( 50 75 2 max 3. Vaux: Make sure Vaux voltage is higher than Vin (power source output) by the voltage required to fully enhance the MOSFET. In this case there is sufficient headroom on the Vaux supply to increase the Vgs level for a reduction in power dissipation due to lower Rds(on). If the MOSFET requires 8.0V to achieve lower power dissipation, then Vaux = Vin + Vgs + 0.5V = 12V + 8.0V + 0.5V = 20.5V. When Vin is off (0V), PI2001 GND pin is at 0V and Vaux is higher than the VC clamp voltage. A bias resistor (Rbias) is needed in series with the VC pin. Rbias value: Ω = − = − = K mA V V IC VC Vaux Rbias clamp 45 . 1 2 . 4 5 . 15 6 . 21 max min or 1.30KΩ Rbias resistor power dissipation rating: Note: Use minimum value for VCClamp voltage to calculate worst condition power dissipation. mW K V V Rbias VC Vaux Pd clamp Rbias 100 30 . 1 ) 0 . 15 4 . 26 ( ) ( 2 2 max = Ω − = − = Figure 16: PI2001 in floating application: example 2 Picor Corporation • picorpower.com PI2001 Rev 1.0 Page 17 of 23 |
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