Gate

ON

Gate

OFF

Programmable

Fast Turn-off

ThresholdRange

TPS2419

SLVS998A – FEBRUARY 2010 – REVISED MARCH 2010

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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

threshold. Operation of the TPS2419 is demonstrated in Figure 8 where an ac-coupled square wave is applied

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 mA 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.

(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.

10

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