(

)

æ

ö

ç

÷

è

ø

v2

t

= - R × C

× ln

DLY

(FLTR)

v -v

2 1

(4)

Source

Load

A

C

FLTR

Fast

Comparator

Turn-on

Amplifier/

Comparator

v

1

t

DLY

time

Comparator Input

Bus Transient

v

1

t

DLY

time

Comparator Input

Bus Transient

Dt

DLY

V2

V1

V1

V2

TPS2410

TPS2411

Gate drive of 270

µA typical is generated by an internal charge pump and current limiter. A separate supply, V

is provided to avoid having the large charge pump currents interfere with voltage sensing by the A and C pins.

capacitor on BYP (bypass) must be used in order to form a quiet supply for the internal high-speed comparator.

The FLTR (filter) pin enables a simple method of filtering the input to the fast turn-off comparator as

demonstrated in Figure 14. To minimize the impact of a bus fault, the ORing controller turns off the external

MOSFET as fast as possible when a voltage reversal occurs. However, having a fast reaction increases the

likelihood that noise or non-fault transients may cause false triggering. Examples of such transients are ESD,

EFT, RF induction, step loads, and insertion of high-inrush units. The effect of the filter on a time-domain

transient are illustrated by assuming a step input from positive to negative. The expression for the time to reach 0

V across the fast comparator inputs follows, where the variables are defined in Figure 14.

Figure 14 graphically illustrates that the external MOSFET is turned off after a longer delay for a small transient

than a large voltage reversal. For example, the delay from 10 mV forward to 10-mV reverse is about 52 ns (R =

520

Ω, C = 150 pF), while the delay for a 100-mV reverse transient is 7 ns. It is unlikely that the transient in a

real system is a step response, making exact calculations on the effect of the R-C filter to a specific transient

difficult.

the electrical environment is understood, the need for the filter, or its value, is selected based on approximations

or simulations. If the system is not understood or does not exist when the TPS2410 circuit design is completed, it

Figure 14. Fast Comparator Input Filtering

18

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