Datasheet

2
LIM(ACT) VCC(MAX)
LIM(ACT) 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
VCC(MAX)
LIM(ACT) VCC(MAX) LIMIT(NOM)
LIMIT(NOM)
V
For P V I
I
O
ON
C
: t
´
³ ´ =
2
2
LIM(ACT) VCC(MAX)
2 2
LIMIT(NOM) LIM(ACT)
P V
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
SOURCE(MAX)
T O-TOL T-TOL
TMR-TH(MAX)
I
C 1 C C
V
ON
t ( )= ´ ´ + +
T
34
C 416 1 0 2 0 1 4 48
4.1V
= ´ ´ + + =
A
s ( . . ) . nF
m
m
1 2
EN_H(MAX)
1 55 22
V
ON
EN EN
V
R R ( ) . k= ´ - = W
1 2 1 2
EN_H(MAX) EN_L(MIN)
2 2
V V
EN EN EN EN
ON OFF
EN EN
R R R R
V ,V
R R
+ +
= ´ = ´
54 9 10
138 8 96
10
ON
. k k
V . V . V
k
W + W
= ´ =
W
54 9 10
122 7 92
10
OFF
. k k
V . V . V
k
W + W
= ´ =
W
TPS2480
TPS2481
www.ti.com SLUS939B –APRIL 2010–REVISED DECEMBER 2010
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 next
equation calculates t
ON
for both the power limit and current limit cases and assumes that only C
O
draws current
during startup.
(17)
(18)
(19)
The next equation allows C
T
to be selected assuming that only C
O
draws current during startup. TPS2480/81
timer current source and capacitor tolerances are accounted for.
(20)
(21)
• Choose C
T
= 0.01 µF
5. Choose the Turn On Voltage, V
ON
and the EN Resistors, R
EN1
and R
EN2
When the EN pin is used as an analog control, the desired turn on voltage, V
ON
can be used to select the EN
resistors. Select R
EN1
and R
EN2
taking into account device leakage currents. Choose R
EN2
=10 kΩ.
(22)
• Choose R
EN2
= 54.9 kΩ
The actual turn on and turn off voltages, VON(ACT) and VOFF(ACT) can be calculated as follows:
(23)
(24)
(25)
Copyright © 2010, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Link(s): TPS2480 TPS2481