PI2123 Datasheet, PDF (14/20 Pages) Vicor Corporation – 15 Volt, 15 Amp Full-Function Active ORing Solution

VC voltage lower than required to drive the gate of
the internal MOSFET.
Select the value of Rbias using the following
equations:
Rbias = ^{Vauxmin − VCclamp}
IC _max
Rbias maximum power dissipation:
Pd _Rbias
=
(Vaux_max −VC_clamp ) ²
Rbias
Where:
Vaux_min : Vaux minimum voltage
Vaux_max : Vaux maximum voltage
VC_Clamp : Controller clamp voltage, 15.5V
IC_max : Controller maximum bias current, use
4.2mA
Example: Vaux 20V to 30V
Rbias = ^{Vauxmin − VCclamp} = ^{20V − 15.5V} = 1.07KΩ
IC_max
4.2mA
Pd _Rbias
=
(Vaux_max − VC_clamp ) ²
Rbias
=
(30V − 15.5V )²
1.07KΩ
= 196mW
Internal N-Channel MOSFET BVdss:
The PI2123’s internal N-Channel MOSFET
breakdown voltage (BVdss) is rated for 15V at 25°C
and will degrade at -40°C to 14.4V, refer to Figure
10. In an application when the MOSFET is turned
off due to a reverse fault, the series parasitic
elements in the circuit may contribute to the
MOSFET being exposed to a voltage higher than its
voltage rating.
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
generate 1.8µJ (½Li²). When the MOSFET is turned
off, the stored energy will be released and produce a
high negative voltage 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. To
reduce the magnitude of the ringing voltage, add a
ceramic capacitor very close to the source that can
react to the voltage ringing frequency and another
capacitor close to the drain. Recommended values
for the ceramic capacitors are 1µF, refer to C5 and
C7 in Figure 23.
Slave:
For a high current application where one PI2123 can
not handle the total load current, multiple PI2123’s
can be paralleled in a master/slave configuration to
support the total current per input. In the
Master/Slave mode, one PI2123 is configured as the
master and the rest are configured as slaves. The
slave ( SL ) pin of the master unit will act as an
output driving the units configured in slave mode.
The SL pins of the slave units will act as inputs
under the control of the master.
Tie the BK pin to VC to configure the unit in slave
mode.
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 internal MOSFET.
The PI2123 internal MOSFET power dissipation can
be calculated with the following equation:
Pd _MOSFET = Is ² ∗ Rds(on)
Where:
Is
: Source Current
Rds(on) : MOSFET on-state resistance
Note:
Calculate with Rds(on) at maximum MOSFET
temperature because Rds(on) is temperature
dependent, Refer to figure 11 for normalized
Rds(on) values over temperature. PI2123 nominal
Rds(on) at 25°C is 3mΩ and will increase by ~40%
at 125°C junction temperature.
The Junction Temperature rise is a function of power
dissipation and thermal resistance.
Trise= Rth_JA ∗ Pd_MOSFET = Rth_JA ∗ Is² ∗ Rds(on) ,
Where:
Rth_JA : Junction-to-Ambient thermal resistance
(54°C/Watt)⁽³⁾
This may require iteration to get to the final junction
temperature. Figures 13, 14 and 17 show the
PI2123 internal MOSFET final junction temperature
Picor Corporation • picorpower.com
PI2123
Rev 1.0 Page 14 of 20