Datasheet

TPS2363
www.ti.com SLUS680B –JANUARY 2006–REVISED JANUARY 2010
MOSFET R
DS(on)
An important parameter in choosing a FET is the on-resistance, R
DS(on)
. The lower the R
DS(on)
, the smaller the
steady state power dissipation of the MOSFET and the easier to maintain the PCI recommended bus voltage.
Low R
DS(on)
does contribute to excessive currents under short circuit conditions discussed below. The lowest
R
DS(on)
MOSFETs are the most expensive.
VDSS Voltage Drain to Source
To ensure safe operation of the external MOSFET, the drain-to-source voltage rating should be reasonably
higher than V
IN
. A 2-to-1 or 3-to-1 ratio of the V
DSS
to V
IN
is recommended.
V
DSS
> 2 x V
IN
ID Drain Current (continuous)
To handle steady state loading, the current rating of the MOSFET at the maximum case temperature (usually
70°C − 100°C), ID, should be at least:
2 x I
TRIP(max)
(see R
SENSE
Calculations Section).
I
D
at T
C(max)
> 2 x I
TRIP(max)
IDM Pulsed Drain Current (plus PD and SOA)
To handle steady state loading, the current rating of the MOSFET at the maximum case temperature (usually
70°C − 100°C), ID, should be at least:
2 x I
TRIP(max)
(see R
SENSE
Calculations Section).
I
D
at T
C(max)
> 2 x I
TRIP(max)
IDM Pulsed Drain Current (plus PD and SOA)
TPS2363 has short circuit output protection. The MOSFET is exposed to large power dissipation for a maximum
of 500 ns. During this time, the current is the supply voltage / (R
DS(on)
+ R
SENSE
). When an excessive current
spike occurs, the MOSFET carries the trip point current at the supply voltage for the duration of the fault time.
Ratings for maximum power dissipation in the device and safe operating area must be considered along with
IDM calculation in device selection:
IDM, PD, and SOA calculated
VGS Voltage Gate to Source
The gate-to-source voltage rating, VGS of the 3.3-V MOSFET should be at least 15 V because the TPS2363
3.3-V gate voltages can be as high as 15 V and the source voltage can be shorted to ground.
VGS(3.3) > 15 V
The VGS of the 12-V MOSFET should be 15 V because the TPS2363 gate voltage is as low as 0 V when the
source is 15 V.
VGS(12) = 15 V
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