PI2001 datasheet(17/23 Pages) VICOR

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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

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

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:

Rds

reverse

Vth

reverse

)

(

−

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%.

∗

Rds

)

(

maximum at 100°C

)

(

Rds

Rth

Trise

∗

Maximum Junction temperature

Trise

max

⎟

⎠

⎞

⎜

⎝

⎛

∗

102

)

(

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:

−

Vaux

Rbias

clamp

max

min

or 1.30KΩ

Rbias resistor power dissipation rating:

Note: Use minimum value for VCClamp voltage to

calculate worst condition power dissipation.

Rbias

Vaux

clamp

Rbias

100

)

(

)

(

max

−

Figure 16:

PI2001 in floating application: example 2

Picor Corporation • picorpower.com

PI2001

Rev 1.0

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