(

)

(

)

(

)

T_M1x

ISS

ADD

OUTx

RSS

ADD

ISS

ADD

TMR_MIN

G

G

G

V

C

+ C

V

× C

+ C

6× C

+ C

t

=

+

+

I

I

I

LOAD

INTER-

CONNECT

INTER-

CONNECT

POWERSUPPLY

TPS2456

GAT1x

GAT2x

OUTx

INx

SENMx

SENPx

1kW

100

100

BlockingMOSFET

ProtectionMOSFET

ESD

Diode

ESD

Diode

ESD

Diode

ESD

Diode

R

LOAD

E=LI

OUTPUT

E=LI

E=LI

E=LI

+

INPUT

TPS2456

www.ti.com

SLVSA78A – MARCH 2010 – REVISED MARCH 2010

ramp requires lower peak current, but takes longer to charge the output capacitance. The length of the fault time

needs to be selected to accomodate this longer ramp up time. The minimum time the fault timer should be set to

is described by Equation 22.

(22)

BYPASS CAPACITORS

It is a good practice to provide low-impedance ceramic capacitor bypassing of INx and OUTx. Values in the

range of 10 nF to 1 µF are recommended. Some system topologies are insensitive to the values of these

capacitors; however, some are not and prefer to minimize the value of the bypass capacitor.

Input capacitance on a plug-in board may cause a large inrush current as the capacitor charges through the low

impedance power bus when inserted. This stresses the connector contacts and causes a short voltage sag on

the input bus. Small amounts of capacitance (e.g., 10 nF to 0.1 µF) are often tolerable in these systems.

Filter capacitors at the output of a redundant plug-in board are useful for controlling voltage transients, but they

may can cause problems when the board is inserted into an active bus. If the output capacitor charge from an

active bus is not limited, the inrush surge might engage the active supply's fast-trip shutdown. One possible

solution is to put a few Ohms of resistance in series with the capacitor to limit inrush below the fast trip level.

TRANSIENT PROTECTION

If the TPS2456 is used in applications which have large input and output capacitors, voltage transients during

load steps or short circuits are controlled and pose no problems.

TPS2456 devices are sometimes deployed systems that may have long, inductive feed or load interconnections.

The effect of the inductance, with little local capacitance, gives rise to potential voltage transient issues. A

simplified model of this is shown in Figure 22. Channel current transients may be caused by events such as

hot-plug, output shorts with fast turnoff, or abrupt load changes. The combination of input inductance and an

abrupt load decrease causes a positive voltage spike on the TPS2354 INPUT pins. The combination of output

inductance and an abrupt load decrease will cause a negative voltage spike on the TPS2354 OUTPUT. These

transients have the potential to exceed the Absolute Maximum Ratings, either damaging the TPS23754 or

causing undesired operation.

Figure 22. System Transient Model

Copyright © 2010, Texas Instruments Incorporated

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