PI2003-00-QEIG View Datasheet(PDF) - Vicor
Part Name
Description
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PI2003-00-QEIG Datasheet PDF : 16 Pages
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current fault has been detected. In Active ORing
applications when one of the input power sources is
shorted, a large reverse current is sourced from the
circuit output through the MOSFET. Depending on
the output impedance of the system, the reverse
current may reach over 60A in some conditions
before the MOSFET is turned off. Such high current
conditions will store energy even in a small parasitic
element. For example, a 1nH parasitic inductance
with 60A reverse current will store 1.8µJ (½Li2).
When the MOSFET is turned off, the stored energy
will be released and will produce high negative
voltage ringing at the MOSFET source. This event
will create a high voltage difference across the drain
and source of the MOSFET.
The MOSFET current rating and maximum power
dissipation are closely related. Generally the lower
the MOSFET Rds(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 Rds(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 ∗ Rds(on)
Where :
Is
: Source Current
Rds(on) : MOSFET on-state resistance
Note:
In the calculation use Rds(on) at maximum MOSFET
temperature because Rds(on) is temperature
dependent. Refer to the normalized Rds(on) curves
in the MOSFET manufacturers datasheet. Some
MOSFET Rds(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.
TriseMOSFET = RthJA ∗ PdMOSFET = RthJA ∗ Is2 ∗ Rds(on) ,
Where:
RthJA : Junction-to-Ambient thermal resistance
Rds(on) and PI2003 sensing:
The PI2003 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 =
Rds(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 PI2003 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.
Under normal conditions the GATE pin output
voltage will rail to the VC voltage minus 0.5V, where
the VC output is regulated to 11V typically to support
any MOSFET with a Vgs rating of ±12V or greater. A
Vgs rating ≥ 12V is very common for industry
standard N-Channel MOSFETs.
Picor Corporation • picorpower.com
PI2003
Rev 1.0
Page 11 of 16
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