Datasheet

J(MAX2) A(MAX) CA JC
T 150 T 50 R 9 8 R 0 2 1 18= = = = = W
DS( on )
C C
C, C, . , . ,R . m
W W
q q
2
J(MAX2) CA LIMIT(NOM) DSON A(MAX)
LIM
C
0.7*(T R I R T
P 249
R
- ´ ´ -
= =
J
)
W
q
q
REF OUT(NOM) LIMIT(NOM)
V 4 1 V 12 I 50
S
V ,R m , V , A= = W = =
REF
LIM(MAX)
1V V
P 2
2
S
kW
R
´
= =
´
OUT(NOM) OUT(NOM) LIMIT(NOM)
P V I 12 50 600V A W= ´ = ´ =
LIM(ACT) S
PROG
2 P R
2 249W 1mΩ
V 0.498V
1V 1V
´ ´
´ ´
= = =
REF
PROG1 PROG2
PROG
V
R R ( 1) 140.6kΩ
V
= ´ - =
010 8 6 4 2 0
0
10
20
30
40
50
60
Current Limit vs. Vout (Vvcc=12V)
Output Voltage (V)
O u tp u t C u r r e n t ( A m p s )
TPS2480
TPS2481
SLUS939B –APRIL 2010–REVISED DECEMBER 2010 www.ti.com
3. Choose the Power Limit P
LIM
and the PROG Resistors, R
PROG1
and R
PROG2
M1 dissipates large amounts of power during power-up or output short circuit. Power limit, P
LIM
should be set to
prevent M1 die temperature from exceeding a short term maximum temperature, T
J(MAX2)
. Short term T
J(MAX2)
may be set as high as 150°C while still leaving ample margin for the typical manufacturer's rating of 175°C. P
LIM
can be estimated as follows:
(10)
(11)
Where R
qCA
is M1+PCB case-to-ambient thermal resistance, R
qJC
is M1 junction-to-case thermal resistance,
R
DS(on)
is M1 channel resistance at the maximum operating temperature, and the factor of 0.7 accounts for the
tolerance of the constant power engine. The maximum power limit for the constant power engine, P
LIM(MAX)
and
nominal power P
OUT(nom)
settings for this circuit are calculated with the next equation:
(12)
(13)
(14)
The PROG resistors should be chosen using the smallest of P
LIM
, P
LIM(MAX)
, or P
LIM(MAX)
values. Choose R
PROG2
= 20 kΩ . Choose R
PROG1
as shown below.
(15)
(16)
• Choose R
PROG1
= 140 kΩ
The power and current limit curve for this configuration is shown in Figure 18.
Figure 18. TPS2480/81 Power and Current Limit Curve
22 Submit Documentation Feedback Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): TPS2480 TPS2481