Datasheet

SENSE
S
LIMIT
V
50mV
R 1.042mΩ
1.2 I 1.2 40A
= = =
´ ´
LIMIT(MAX)
S
55
I 55
R 1mΩ
SENSE( MAX )
V
mV
A= = =
2 2
LIMIT(MAX)
I 55 1 3 025
S S
R Power R A m . W= ´ = ´ W =
J(MAX) A(MAX) JA LIMIT(NOM)
T 125 T 50 R 10 I 50= = = =
C
C, C, , A
W
q
J(MAX) A(MAX)
DSON(MAX)
2
2
JA LIMIT(NOM)
T T
125C 50C
R 3mΩ
R I
10 (50A)
-
-
= = =
´
´
C
W
q
TPS2480
TPS2481
www.ti.com SLUS939B –APRIL 2010–REVISED DECEMBER 2010
1. Choose R
S
The following equation includes a factor of 1.2 (20%) for V
SENSE
and R
S
tolerance along with some additional
margin.
(5)
• Choose R
S
= 1 mΩ
(6)
(7)
Multiple sense resistors in parallel should be considered.
2. Choose M1
Select the M1 V
DS
rating allowing for maximum input voltage and transients. Then select an operating R
DSON
,
package, and cooling to control the operating temperature. Most manufacturers list R
DSON(MAX)
at 25°C and
provide a derating curve from which values at other temperatures can be derived. The next equation can be used
to estimate desired R
DSON(MAX)
at the maximum operating junction temperature of T
J(MAX)
. (usually 125°C). T
A(MAX)
is the maximum expected ambient temperature.
(8)
(9)
The junction-to-ambient thermal resistance R
qJA
, depends upon the package style chosen and the details of
heat-sinking and cooling including the PCB. Actual “in-system” temperature measurements will be required to
validate heat-sinking and cooling performance.
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