PI2002 Datasheet, PDF (18/23 Pages) Vicor Corporation – Active ORing Controller IC with Load Disconnect Feature

Typical application Example 2:
Low side disconnect switch
Requirement:
Bus Voltage = -48V (-36V to -60V, 100V for 100ms
transient)
Maximum operating load current = 5A
Load current shutdown set at = 6A
Maximum Ambient Temperature = 60°C
Solution:
1. A PI2002 with a suitable MOSFET for -48V
power source should be used and configured as
shown in Figure 22. The VC is biased from the
return line through a bias resistor.
2. Select a suitable N-Channel MOSFET: Select
the N-Channel MOSFET with voltage rating
higher than the input voltage, Vin, plus any
expected transient voltages, with a low Rds(on)
that is capable of supporting the full load current
with margin. For instance, a 100V rated
MOSFET with 10A current capability is suitable.
An exemplary MOSFET having these
characteristic is Si4486EY from Vishay Siliconix.
From Si4486EY datasheet:
• N-Channel MOSFET
• V_DS= 100V
• I_D = 23A continuous drain current at 125°C
• VGS(MAX) = ± 20V
• R_θJA= 50°C/W
• R_DS(on)=20mΩ typical at V_GS=10V, T_J=25°C
Reverse current threshold is:
Is.reverse
=
Vth.reverse
Rds(on)
=
− 6mV
20mΩ
= −300mA
Power dissipation:
Rds(on) is 25mΩ maximum at 25°C & 10Vgs and
will increase as the temperature increases. Add
40°C to maximum ambient temperature to
compensate for the temperature rise due to power
dissipation. At 100°C (60°C + 40°C) Rds(on) will
increase by 63%.
Rds(on) = 25mΩ∗1.63 = 41mΩ maximum at 100°C
Maximum Junction temperature
T_J
max
=
60°C
+
⎜⎛
⎝
50°C
W
∗
(5.0A)²
∗
41mΩ⎟⎞
⎠
=
111°C
Recalculate based on calculated Junction
temperature, 111°C.
Picor Corporation • picorpower.com
At 111°C Rds(on) will increase by 71%.
Rds(on) = 25mΩ∗1.71= 4.75mΩ maximum at 111°C
T_J
max
=
60°C
+
⎜⎛
⎝
50°C
W
∗
(5.0A)²
∗
42.75mΩ⎟⎞
⎠
=
113°C
Vaux: Connect each controller to the return path
with a separate bias resistor, Rbias.
To reduce Rbias power dissipation, VC_clamp is
selected at 13V which is less than the actual PI2002
clamp voltage (15V typical). 13V is higher than
PI2002 maximum gate clamp voltage (11V).
Rbias = ^{Vauxmin − VCclamp}
IC _max
=
36V − 13V
4.2mA
= 5.48KΩ
or 5.49KΩ
Rbias maximum power dissipation is at maximum
input voltage and minimum clamp voltage
Pd _Rbias
=
(Vaux_max −VC_clampMIN ) ²
Rbias
=
(60V −15V ) ²
5.49KΩ
= 369mW
3. Select sense resistor: Sense resistor is
selected based on load current shutdown.
Where
R_Sense
= ^VFOC−TH
I _Shutdown
=
114 mV
6A
= 19mΩ
Select 20mΩ resistor
20mΩ Sense Resistor power dissipation at
maximum operating current
Pd _RSense
=
I2
max
* R_Sense
= (5A) ² 20mΩ
= 0.5W
As an exemplary selected 1206 20mΩ/1W/1%
sense resistor from Vishay-Dale:
Part Number: WSL1206R0200FEK
Maximum current turn off:
Isd _MAX
= ^{VFOC−TH −MAX}
R_Sense
=
121mV
20mΩ
= 6.05A
Minimum current turn off:
Isd _MIN
= ^{VFOC−TH −MIN}
R_Sense
=
107mV
20mΩ
= 5.35A
4. SP and SN pins: Connect the SP pin to the
MOSFET source and controller GND pin, and
connect the SN pin to Vin- and the drain of the
MOSFET.
PI2002
Rev1.1 Page 18 of 23