Datasheet

V
(AC)
V
(GATE)
V
ON
Gate
ON
Gate
OFF
3mV
Programmable
Fast Turn-off
ThresholdRange
TPS2419
SLVS998B –FEBRUARY 2010–REVISED SEPTEMBER 2011 www.ti.com
APPLICATION INFORMATION
OVERVIEW
The TPS2419 is designed to allow an output ORing in N+1 power supply applications (see Figure 11), and an
input-power bus ORing in redundant source applications (see Figure 12). The TPS2419 and external MOSFET
emulate a discrete diode to perform this unidirectional power combining function. The advantage to this
emulation is lower forward voltage drop and higher efficiency.
The TPS2419 turns the MOSFET on and off like a comparator with hysteresis as shown in Figure 10. GATE is
driven high when V
(A-C)
exceeds 65 mV, and driven low if V
(A-C)
falls below the RSET programmed turn-off
threshold. Operation of the TPS2419 is demonstrated in Figure 8 where an ac-coupled square wave is applied
from A to C. Figure 8 shows the condition where the MOSFET gate is initially at GND, and V
(A-C)
is less than 65
mV. When the turn-on threshold is exceeded, the TPS2419 turns on the MOSFET gate, and charges it to V
(BYP)
.
The gate stays high even though V
(A-C)
is less than the turn-on threshold. The TPS2419 pulls the gate to GND
when V
(A-C)
falls below the turn-off threshold.
System designs should account for the inherent delay between a TPS2419 circuit becoming forward biased, and
the MOSFET actually turning ON. The delay is the result of the MOSFET gate capacitance charge from ground
to its threshold voltage by the 290 μA gate current. If there are no additional sources holding a common ORed
rail voltage up, the MOSFET internal diode will conduct and maintain voltage on the ORed output. The ORed
input supply will experience a momentary large current draw as the MOSFET turns on, shorting the internal diode
and charging the bus capacitance.
Figure 10. TPS2419 Operation
The operation of the TPS2419 is summarized in Table 2.
Table 2. Operation as a Function of V
(AC)
V
(A-C)
≤ Turnoff Threshold
(1)
Turnoff Threshold
(1)
≤ V
(A-C)
≤ 65 mV V
(A-C)
> 65 mV
Depends on previous state
(1)
TPS2419 Gate pulled to GND GATE pulled high (ON)
(Hysteresis region)
(1) Turnoff threshold is established by the value of RSET.
N+1 POWER SUPPLY – TYPICAL CONNECTION
The N+1 power supply configuration shown in Figure 11 is used where multiple power supplies are paralleled for
either higher capacity, redundancy or both. If it takes N supplies to power the load, adding an extra identical unit
in parallel permits the load to continue operation in the event that any one of the N supplies fails. The supplies
are ORed together, rather than directly connected to the bus, to isolate the converter output from the bus when it
is plugged-in or fails short. Thus, the TPS2419 with an external MOSFET emulates the function of the ORing
diode.
ORed supplies are usually designed to share power by various means, although the desired operation could
implement an active and standby concept. Sharing approaches include both passive, or voltage droop, and
active methods. Not all of the output ORing devices may be ON depending on the sharing control method, bus
loading, distribution resistances, and tolerances.
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Product Folder Link(s): TPS2419