PI2126 Datasheet, PDF (11/15 Pages) Vicor Corporation – 30 Volt, 12 Amp Full-Function Active ORing Solution

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the load through the MOSFET. Depending on the output
impedance of the system and the parasitic inductance, the
reverse current in the MOSFET may exceed the source
pulsed current rating (60A) before the PI2126 MOSFET is
turned off.
The peak current during an input short condition is
calculated as follows, assuming that the output has very
low impedance and it is not a limiting factor:
Where:
: Peak current in PI2126 MOSFET before it is
turned off.
:
Input voltage or load voltage at S pin before
input short condition did occur.
: Reverse fault to MOSFET turn-off time.
: Circuit parasitic inductance
The high peak current during an input short stores energy
in the circuit parasitic inductance, and as soon as the
MOSFET turns off, the stored energy will be released and
this will produce a high negative voltage and ringing at the
MOSFET source. At the same time the energy stored at the
drain side of the internal MOSFET will be released and
produce a voltage higher than the load voltage. This event
will create a high voltage difference between the drain and
source of the MOSFET. The MOSFET may avalanche, but
this avalanche will not affect the MOSFET performance
because the PI2126 has a fast response time to the input
fault condition and the stored energy will be well below
the MOSFET avalanche capability.
MOSFET avalanche during input short is calculated as
follows:
Where:
:
Avalanche energy
: MOSFET breakdown voltage (30V)
Power dissipation:
In Active ORing circuits the MOSFET is always on in steady
state operation and the power dissipation is derived from
the total source current and the on-state resistance of the
MOSFET.
The PI2126 internal MOSFET power dissipation can be
calculated with the following equation:
Where:
: MOSFET power dissipation
:
Source Current
: MOSFET on-state resistance
Note: For the worst case condition, calculate with
maximum rated R_DS(on) at the MOSFET maximum operating
junction temperature because R_DS(on) value is directly
proportional to temperature. Refer to Figure 10 for
normalized R_DS(on) values over temperature. The PI2126
maximum R_DS(on) at 25°C is 6mΩ and will increase by 40% at
125°C junction temperature.
The Junction Temperature rise is a function of power
dissipation and thermal resistance.
Where:
: Junction-to-Ambient thermal resistance, 46°C/W
This may require iteration to get to the final junction
temperature. Figure 13 and Figure 14 show the PI2126
internal MOSFET final junction temperature curves versus
conducted current at maximum R_DS(on), given ambient
temperatures and air flow.
Picor Corporation • picorpower.com
PI2126
Rev 1.1
Page 11 of 15