Datasheet

T
36
C 416 1 0 2 0 1 4 75
4.1V
= ´ ´ + + =
A
s ( . . ) . nF
m
m
SOURCE(MAX)
T O-TOL T-TOL
TMR-TH(MAX)
I
C 1 C C
V
ON
t ( )= ´ ´ + +
2
2
VCC(MAX)
LIM
2 2
LIMIT(NOM) LIM
V
P
1000 13 5
1000 249W
416
2 I 2 P 2 50 2 249W
´
´
´
´
= + = + =
´ ´ ´ ´
O
O
ON
C
C
F . V
F
t s
A
m
m
m
( )
VCC(MAX)
LIM VCC(MAX) LIMIT(NOM)
LIMIT(NOM)
V
For P V I
I
´
³ ´ =
O
ON
C
: t Current Limit Only
( )
2
LIM(ACT) VCC(MAX)
LIM VCC(MAX) LIMIT(NOM)
2
LIMIT(NOM) LIM(ACT)
P V
For P V I
2 I 2 P
´ ´
< ´ = +
´ ´
O O
ON
C C
: t Power Limit
TPS2492
TPS2493
www.ti.com SLUSA65C –JULY 2010–REVISED JANUARY 2013
4. Choose the TIMER Capacitor, C
T
and Turn-On Time
The turn on time t
ON
, represents the time it takes the circuit to charge up the output capacitance C
O
and load. C
T
programs the fault time and should be chosen so that the fault timer does not terminate prior to completion of
start up. The turn on time is a function of the type of control; current limit, power limit, or dV/dt control. The
following equations calculates t
ON
for the power limit and current limit cases, and assume that only C
O
draws
current during startup.
(12)
(13)
(14)
The next equation computes C
T
for a TPS2492 application. TPS2492/93 TIMER current source and capacitor
tolerances are accounted for.
(15)
(16)
Choose C
T
= 6.8 nF assuming a 20% output capacitor tolerance and a 10% timing capacitor tolerance.
Equation 16 is written around startup for a TPS2492, however during a restart (after a fault) of a TPS2493, C
T
charges from 1 V to 4.1 V, requiring a V
TMR-TH(MAX)
value of 3.1V.
The maximum TIMER period may be calculated using the minimum TIMER charge current and maximum value
of C
T
. Use this period to determine the transient R
θJC
in step 3. While this is beyond the scope of this example, it
may lead to some iteration.
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