PI2007 Datasheet, PDF (12/19 Pages) Vicor Corporation – Universal High Side Active ORing Controller IC


Where:
I _PEAK : Peak current in the MOSFET right before it
is turned off.
V_S :
Input voltage or load voltage at MOSFET
source before input short condition did
occur.
t _RVS :
Reverse fault to MOSFET turn-off time. This
will include PI2007 delay and the MOSFET
turn off time.
L_PARASITIC : Circuit parasitic inductance
And the MOSFET avalanche energy during an input
short is calculated as follows:
E _AS

1 _* ^{1.3 *V}_(BR)DSS
2 *1.3V_(BR)DSS  V_S
* L_PARASITIC
* I _PEAK ²
Where:
E _AS : Avalanche energy
V_(BR)DSS : MOSFET breakdown voltage
MOSFET R_DS(on) and maximum steady state power
dissipation are closely related. Generally the lower the
MOSFET R_DS(on), the higher the current capability and
the lower the resultant power dissipation. This leads to
reduced thermal management overhead, but will
ultimately be higher cost compared to higher R_DS(on)
parts. It is important to understand the primary design
goal objectives for the application in order to
effectively trade off the performance of one MOSFET
versus another.
Power dissipation in active ORing circuits is derived
from the total source current and the on-state
resistance of the selected MOSFET.
MOSFET power dissipation:
Pd _MOSFET  Is ²  R_{DS (on)}
Trise_MOSFET  Rth_JA  Pd _MOSFET  Rth_JA  Is ²  R_{DS (on)} ,
Where:
Rth_JA : Junction-to-Ambient thermal resistance
R_DS(on) and PI2007 sensing:
The PI2007 senses the MOSFET source-to-drain
voltage drop via the SP and SN pins to determine the
status of the current through the MOSFET. When the
MOSFET is fully enhanced, its source-to-drain voltage
is equal to the MOSFET on-state resistance multiplied
by the source current, VSD = R_DS(on)*Is. The reverse
current threshold is set for -6mV and when the
differential voltage between the SP & SN pins is more
negative than -6mV, i.e. SP-SN-6mV, the PI2007
detects a reverse current fault condition and pulls the
MOSFET gate pin low, thus turning off the MOSFET
and preventing further reverse current. The reverse
current fault protection disconnects the power source
fault condition from the redundant bus, and allows the
system to keep running.
Where :
Is :
Source Current
R_DS(on) : MOSFET on-state resistance
Note:
In the calculation use R_DS(on) at maximum MOSFET
temperature because R_DS(on)
is temperature
dependent. Refer to the normalized R_DS(on) curves in
the MOSFET manufacturers datasheet. Some
MOSFET R_DS(on) values may increase by 50% at
125°C compared to values at 25°C.
The Junction Temperature rise is a function of power
dissipation and thermal resistance.
Picor Corporation • picorpower.com
PI2007
Rev 1.3
Page 12 of 19