PI2123 Datasheet, PDF (16/20 Pages) Vicor Corporation – 15 Volt, 15 Amp Full-Function Active ORing Solution

Typical Application Example 1:
Requirement:
Redundant Bus Voltage = 5.0V
Load Current = 12A (assume through each
redundant path)
Maximum Ambient Temperature = 75°C: no air flow.
Auxiliary Voltage = 12V (10V to 14V)
Solution:
A single PI2123 for each redundant 5.0V power
source should be used, configured as shown in the
circuit schematic in Figure 22.
Vaux: Since the Vaux voltage does not exceed the
VC pin clamp voltage, connect the Vaux directly to
the VC pin
SP and SN pins: Connect each SP pin to the S pins
and each SN pin to the D pins
BK pin: Connect the BK pin to the ground to
achieve the minimum reverse current response time.
SL pin: Not required, so leave floating
FT pin: Connect to the logic input and to the logic
power supply via a 10KΩ resistor.
Program UV and OV to monitor input voltage:
Program UV at 4.5V and OV at 5.5V
Use the three-resistor divider configuration:
I _Ra = 200μA
Ra = ^500mV = 2.5kΩ ^{or 2.49kΩ 1%}
200μA
Rb = 2.49kΩ⎜⎛ ^5.5V − 1⎟⎞ = 553Ω ^{or 549Ω 1%}
⎝ ^4.5V ⎠
Rc = (2.49kΩ + 549Ω)⎜⎛ ^4.5V − 1⎟⎞ = 24.3kΩ ^1%
⎝ ^500mV ⎠
Figure 21: Example 1 final junction temperature at
12A/75°C T_A
Rds(on) = 4.0mΩ•1.35 = 5.4mΩ maximum at 117°C
Rth_JA : 54°C/W
T_J = T_A + Rth_JA ∗ Is² ∗ Rds(on)
Recalculate T_J:
T_J
= 75°C + ⎜⎛ ^54°C ∗(12A)² ∗5.4mΩ⎟⎞
⎝^W
⎠
= 116.99°C
Maximum power dissipation at 117°C Junction
Temperature:
Pd_max = Iin² ∗ Rds(on) = (12A)² ∗5.4mΩ = 777mW
Reverse current threshold is:
The following procedure demonstrates how to
calculate the minimum required reverse current in
the internal MOSFET to generate a reverse fault
condition and turn off the internal MOSFET.
Power Dissipation and Junction Temperature:
First use Figure 13 (Junction Temperature vs. Input
Current) to find the final junction temperature at 12A
load current and 75°C ambient temperature. In
Figure 13 (illustrated in Figure 21) draw a vertical
line from 12A to half way between the TA=70°C and
TA=80°C lines. Then draw a horizontal line towards
the Y-axis (Junction Temperature). The Junction
Temperature at full load current (12A) and 75°C
ambient is 117°C.
Rds(on) is 4.0mΩ maximum at 25°C and will
increase as the Junction temperature increases.
From Figure 11, at 117°C Rds(on) will increase by
~35%, then
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At room temperature (25°C) typical Rds(on):
Is.reverse = ^Vth.reverse = ^{− 6mV} = −2.0A
Rds(on) 3.0mΩ
At maximum junction temperature (117°C) and
maximum Rds(on):
Is.reverse = ^Vth.reverse = ^{− 6mV} = −1.11A
Rds(on) 5.4mΩ
PI2123
Rev 1.0 Page 16 of 20