Datasheet

J(MAX) A(MAX)
DSON(MAX) J
2
2
JA LIMIT(NOM)
T T
125°C 50°C
R 3mΩ at T = 125°C
R I
10 (50A)
-
-
= = =
°
´
´
C
W
q
2 2
LIMIT(MAX)
I 55 1 3 025= ´ = ´ W =
RSENSE SENSE
P R A m . W
LIMIT(MAX)
SENSE
55
I 55
R 1mΩ
= = =
SENSE( MAX )
V
mV
A
SENSE
SENSE
LIMIT
V
50mV
R 1.042mΩ
1.2 I 1.2 40A
= = =
´ ´
TPS2492
TPS2493
www.ti.com SLUSA65C –JULY 2010–REVISED JANUARY 2013
1. Choose R
SENSE
Calculate R
SENSE
using a multiplier factor of 1.2 (20%) for V
SENSE
and R
SENSE
tolerance along with some
additional margin.
(5)
Choose R
SENSE
= 1 mΩ, resulting in a nominal 50 A current limit.
(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 typical characteristics 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. Assume that a thermal resistance, R
θJA
of 10 °C/W can be achieved by reinforcing the typical 40°C/W for a 1
2
inch copper pad with copper on multiple
layers and some airflow.
(8)
Assume that we are able to find a suitable FET with an R
DSON
of 0.74 mΩ at 25°C and 1.18 mΩ at 125°C. These
devices are in a package such as a D2PAK with a large copper base and very low R
θJC
.
The junction-to-ambient thermal resistance, R
θJA
, depends upon the package style chosen and the details of
heat-sinking and cooling including the PCB layout. Actual “in-system” temperature measurements will be required
to validate thermal performance.
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