PI2001 Datasheet, PDF (17/23 Pages) Vicor Corporation – Universal Active ORing Controller IC

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
• V_DS= 30V
• I_D = 20A continuous drain current
• VGS(MAX)= ± 20V
• R_θJA= 50°C/W
• R_DS(on)=3.2mΩ typical at I_D=10A,
T_J=25°C
V_GS=8V,
Reverse current threshold is:
Is.reverse = ^Vth.reverse = ^{− 6mV} = −1.87 A
Rds(on) 3.2mΩ
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%.
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:
Rbias = ^{Vauxmin − VCclamp} = ^{21.6V − 15.5V} = 1.45KΩ
IC _max
4.2mA
or 1.30KΩ
Rbias resistor power dissipation rating:
Note: Use minimum value for VC_Clamp voltage to
calculate worst condition power dissipation.
Pd _Rbias
=
(Vaux_max − VC_clamp ) ²
Rbias
=
(26.4V − 15.0V )²
1.30KΩ
= 100mW
Rds(on) = 4.2mΩ∗1.28 = 5.37mΩ maximum at 100°C
Trise= Rth_JA ∗ Is² ∗ Rds(on)
Maximum Junction temperature
T_{J max} = T_A +Trise
T_J
max
=
75°C
+
⎜⎛
⎝
50°C
W
∗
(10A)²
∗
5.37mΩ⎟⎞
⎠
=
102°C
Picor Corporation • picorpower.com
Figure 16: PI2001 in floating application: example 2
PI2001
Rev 1.0 Page 17 of 23