International Rectifier
IRF6644 Active ORing
MOSFETs
IRDC5001-LS370W Active ORing Demo Board
Evaluation Procedure
Using IR5001S Active ORing IC and new 100V IRF6644 DirectFET MOSFET
International Rectifier • 233 Kansas Street, El Segundo, CA 90245 USA
Overview
This document describes how to connect and evaluate the supplied IRDC5001-LS370W Active ORing
demo board. The purpose of this circuit is to demonstrate the Active ORing function for carrier-class
system boards (in which two negative 48V inputs (-36V to -75V range) are OR-ed to provide redundant
board power), and to show how the IR5001S can be used to implement Reverse Polarity protection for –
48V input DC-DC converters. The front side of the demo board is shown in Fig. 1.
Figure 1. IRDC5001-LS370W Active ORing Demo Board
Active ORing Demo Board Quick Evaluation Procedure
The circuit schematic is shown in Fig. 2. The circuit incorporates two IR5001S Active ORing ICs (SO-8
package), and two IRF6644, 10.3mOhm typical Rds(on), 100V, N-Channel active ORing FETs, in the
DirectFET MN package. The IRF644 power MOSFET’s used in this circuit are capable of handling up
to 370W of redundant power across a 36V to 75V range. The IRF6662, 17.5mOhm typical Rds(on),
100V, N-Channel active ORing FET is ideal for up to 200W applications, and this demo board can be
IR5001S Active ORing
Controllers
FET Check LEDs
IR BUS converter
demo boards & std
1/8 and 1/4 Brick
connections
FET Check
Switch
BUS Caps
Input A+
Input B+
Input A-
Input B-
Output+
Out
p
ut-
IRF6644
IRF6644
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modified to test these devices also. For lower power applications, it is recommended to use slightly
higher Rds(on) MOSFET’s, to enable faster response time after a reverse current is detected. As a
general design practice, the active ORing FET should be selected for a Vsd drop of greater then 50mV
during conduction. Eight 3.3uF, 80V aluminum capacitors are connected on the redundant bus.
To evaluate the operation and performance of the active ORing demo board, connect two 48V power
supplies to the input terminals (labeled Input A and Input B), and power load to output terminals.
Caution: One of the IR5001S functional tests is the response to a short circuit of one of the
sources. Before doing this test, it is important that the current limit function of each power
supply be checked first. A safe way to test the current limit function is to set the desired current
limit, then apply a short with a very low output voltage first (<5V), then remove the short,
increase voltage by another 5-10V, apply the short again, and proceed with these steps until the
final test voltage is reached. Extra precautions should be taken for older and larger power
supplies where the current limit may not be fast enough so that shorting of the outputs can pose
safety risks.
To probe the circuit waveforms use an oscilloscope probe with minimal length for the ground pin and
connect directly to the pins of the IC / MOSFET device. Any standard current probe & amplifier can be
used to measure reverse current flow.
0Va
G
S1
g1
0Va
0Vb
g2
G
R5
510
+48V
C1
3.3uFd
+48V
5V
G
R2
510
+48V
C10
1.0uF
C11
1.0uF
D3
5V
D2
R3
20K
D1
Vch
R4
Open
C12
Open
Vline
1
Vcc
2
GND 7
FETCh
3
FETst
4Vout 8
INP 5
INN 6
IC1
IR5001S
R1
Open
G
C9
Open
Vline
1
Vcc
2
GND 7
FETCh
3
FETst
4Vout 8
INP 5
INN 6
IC2
IR5001S
+48V
5V
0Vb
G
g2
G
Vch
g1
5V
Vch
C2
3.3uFd
C3
3.3uFd
C4
3.3uFd
C5
N/A
C6
N/A
C7
N/A
C8
N/A
C13
1.0uF
Q1
IRF6644
Q2
IRF6644
Load +
Load -
Figure 2. IRDC5001-LS370W Active ORing Demo Board Schematic
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The procedure for checking the response tim e of the IR5001S to a simulated short circuit failure of one
power source is shown in Fig. 3. T he power supply B is set at about 1V highe r output voltage than
power Supply A. For e xample, VB = 49V, and V A = 48V. This guarantees that power supply B is
delivering all the power to the lo ad, while power supply A is on sta nd by (has zero output current). A
150W IR2085S DC Bus Converter is used in this example on the output of the demo board.
To perform the test, apply a short circuit across th e output term inals of power supply B. As the bus
voltage drops below 48V (because both power supplies and the redundant bus caps are now sho rted), a
reverse current will start to flow through the act ive ORing MOSFET M2 (in line with source B). The
IR5001S at source B will detect this reverse current flow and will turn M2 MOSFET off in about 120nS,
while allowing only 4A of reverse current flow. This is shown in Fig. 4, which also shows Vds
waveform for the MOSFET M2. When the MOSFET turn s off, the energy stored in the stray leakage
inductance is dissipated in the avalanche m ode that last about 20nS. The calculated avalanche energy is
about 5uJ, which is negligible compared to the 220mJ avalanche rating of IRF6644.
Another waveform shown in Fig. 4 is the redundant bus voltage (green trace). With 48V being delivered
to a 150W bus converter load, with source B shorted, only 3V bus voltage disturbance is observed.
NO1
NO2
Load
VAVB
Figure 3. IR Active ORing functional tests
Short circuit
Current
IR2085S
DC bus
converter
M2
M1
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3: MOSFET Ids (2.5A/div) 2: MOSFET Vgs, 3: MOSFET Vds; 4:Vbus
Figure 4. Waveforms during short circuit test for 150W output, 48V input. Power supplies A and
B were connected to the demo board with a one foot-long cable. Short circuit was applied on the
output terminals of power supply B.
Another unique feature of the IR5001S is that it allows system designers to assess the power redundancy
status on their system boards - whether the ORing FETs are good or not. Applying a logic high at the
“FET Check” pin will toggle the output of the IR5001S driver OFF. The desired outcome is that the
voltage across the FET, Vds, will rise above 0.3V. When “FET check” is initiated for the MOSFET
initially being on, a comparator inside IR5001S compares the Vds voltage to a reference voltage of
0.3V. If the Vds voltage is over 0.3V, the comparator sends a logic-low signal at the “FET Short” pin,
indicating that the FET is working properly.
This feature can be tested on this demo board via a normally-OFF switch and two green LEDs. By
pressing the switch, the gate drive signals from both Active ORing controllers will be turned off, which
will turn off the channels of ORing FETs. The simplest way to test this feature is to disconnect one of
the power sources. For example, disconnect VB and with VA set at 48V, depress the switch. The green
LED next to the IC A will turn on. If a short circuit is applied across the FET A, the LED diode will not
turn on, indicating a FET short circuit. The same procedure can be used to test the ORing FET for
source B (source A would be disconnected, and source B connected).
In a real system, it may not be practical to disconnect one of the sources, and if the voltage of each
source cannot be changed, it will only be possible to determine if one of the FETs, which is connected to
a higher voltage source, is working properly or not. Usually, a truth table as shown in Table 1, can be
applied to determine the status of individual FETs based on various possible status of sources A and B.
Note that this table can determine not only if a FET is short, but also if it is open. For additional
information on how to use FET Check feature, please contact your local IR Field Applications Engineer.
Applied short
Fet turn off
4A reverse
curren
t
3A, 150W
120ns
3V bus voltage disturbance
Vds
V
g
s
0A
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Table 1. Truth table for IR5001S “FET Check Feature”
Case LED Initial During the check Fet A Fet B Comments
A off on
1 B off off
Vsd of fet A > 300mV
Vsd of fet B < 300mV good N/A VA>VB +0.4V
A off on
2 B off on
Vsd of fet A > 300mV
Vsd of fet B > 300mV good good IVA-VBI < 0.4V
Short N/A VA>VB+0.3V
A off off At least
one is short IVA-VBI < 0.3V 3
B off off
Vsd of fet A < 300mV
Vsd of fet B < 300mV
N/A Short VB>VA+0.3V
A on on
4 B off on
Vsd of fet A > 300mV
Vsd of fet B > 300mV Open or
diode good VA>VB+0.3V
A on on Open Short VA>VB+0.3V
5 B off off
Vsd of fet A > 300mV
Vsd of fet B < 300mV Diode N/A IVA-VBI < 0.4V
A on
6 B on
Open or diode
