IR5001S & (PbF)
10
www.irf.com
APPLICATION INFORMATION
The IR5001S is designed for multiple active ORing
and reverse polarity protection applications with
minimal number of external components. Examples
of typical circuit connections are shown below.
Negative Rail ORing/Reverse Polarity Protection
A typical connection of the IR5001S in negative
rail Active ORing or reverse polarity protection is
shown in Fig. 17 . In this exam ple, IR500 1S is b iased
directly from the positive rail. However, any of the
biasing schemes shown in Fig. 16 can be used.
For in put ORing in carrier-class communica tions
boards, one IR5001S is used per feed. This is
shown in Fig.1. An evaluation kit is available fo
typical system boards, with input voltages o
negative 36V to negative 75V, and for power levels
from 30W to about 300W . The p/n for the evaluat ion
kit is IRDC5001-LS48V. This ev aluation k it contains
detailed design considerations and in-circuit
performance data for the IR5001S.
Positive Rail ORing / Ground ORing in
Communications Boards
An example of a typical connection in positive
rail ORing is shown in Fig. 18. Typical applications
are inside redundant AC-DC and DC-DC power
supplies , or on-bo ard ORin g. For positi ve rail O Ring,
an additional Vbias voltage above the positive rail is
needed to bias the IR5001S.
An evaluation kit for high-current 12V positive
rail ORing is available under p/n IRAC5001-
HS100A, demonstrating performance of the
IR5001S at 100A output current.
Considerations for the Selection of the Active
ORing N-Channel MOSFET
Active ORing FET losses are all conduction
losses, and depend on the source-drain current and
RDS(on) of the FET. The conduction loss could be
virtually eliminated if a FET with very low RDS(on)
was used. However, using arbitrarily low RDS(on) is
not desirable for three reasons:
1. Turn off propagation delay. Higher RDS(on) will
provide more voltage information to the internal
comparator, and will result in faster FET turn of
protection in case of short-circuit of the source
(less voltage disturbance on the redundant bus).
2. Undetected reverse (drain to source) current
flow. W ith the asymm etrical offs et voltage, som e
small current can flow from the drain to source
of the ORing FET and be undetected by the
IR5001S. The amount of undetected drain-
source current depends on the RDS(on) of the
selected MOSFET and its RDS(on). To keep the
reverse (drain-source) current below 5 – 10% o
the nominal source-drain state, the RDS(on) o
the selected FET should produce 50mV to
100mV of the voltage drop during nominal
operation.
3. Cost. With properly selected RDS(on), Active
ORing using IR5001S can be very cost
competitive with traditional ORing while
providing huge power loss reduction. For
exam ple, a FET with 20m Ohm R DS(on) results in
60mV voltage drop at 3A; associated power
savings compared to the traditio nal diode ORing
(assuming typical 0.6V forward voltage drop) is
ten fold(0.18W vs. 1.8W)! Now assume that
FET RDS(on) was 10mOhm. The power loss
would be reduced by additional 90mW , which is
negligible compared to the power loss reduction
alread y achieved with 20mOhm FET. But to get
this negligible saving, the cost of the Active
ORing FET would increase significantly.
Vbias
IR5001
Vcc
FETch
INP
INN
Gnd
OUT
FETst
Vline
Rbias
+
Vin +
Vin -
Load
Redundant Vin -
Vbias
IR5001
Vcc
FETch
INP
INN
Gnd
OUT
FETst
Vline
Rbias
+
Vout +
Vout -
Redundant Vout +
Load
Figure. 18. Connection of INN,INP, and Gnd when the
MOSFET is placed in the path of positive rail.
Figure. 17 Connection of INN, INP, and Gnd for negative
rail Active ORing or reverse polarity protection.