Datasheet

LIMIT
SUM3
650 V
I
R
=
TPS2458
SLUS916B –FEBRUARY 2009–REVISED MAY 2010 www.ti.com
3.3-V Current Limiting
The 3.3-V management power channel includes an internal pass FET and current sense resistor. The
on-resistance of the management channel — including pass FET, sense resistor, metallization resistance, and
bond wires — typically equals 290 mΩ and never exceeds 500 mΩ. The AdvancedMC™ specification allows a
total of 1 Ω between the power source and the load. The TPS2458 never consumes more than half of this
budget.
3.3-V Fast Trip Function
The 3.3-V fast trip function protects the channel against short-circuit events. If the current through the channel
exceeds a nominal value of 300 mA, then the TPS2458 immediately disables the internal pass transistor and
then allows it to slowly turn back on into current limiting.
3.3-V Current Limit Function
The 3.3-V current limit function internally limits the current to comply with the AdvancedMC™ and MicroTCA™
specifications. External resistor R
SUM3
allows the user to adjust the current limit threshold. The nominal current
limit threshold I
LIMIT
is shown in Equation 1.
(1)
A 3320-Ω resistor gives a nominal current limit of I
LIMIT
= 195 mA which complies with AdvancedMC™ and
MicroTCA™ specifications. This resistance corresponds to an EIA 1% value. Alternatively, a 3.3-kΩ resistor also
suffices. Whenever the 3.3-V channel enters current limit, its fault timer begins to operate (see Fault Timer
Programming section).
3.3-V Over-Temperature Shutdown
The 3.3-V over-temperature shutdown trips if the 3.3-V channel remains in current limit so long that the die
temperature exceeds approximately 140 °C. When this occurs, the chip turns off until the it cools by
approximately 10 °C. This feature prevents a prolonged fault on one 3.3-V channel from disabling the other 3.3-V
channel, or disabling the 12-V channel.
16 Submit Documentation Feedback Copyright © 2009–2010, Texas Instruments Incorporated
Product Folder Link(s): TPS2458