Datasheet

Time: 200us/div
20V/div
500mA/div
I
PI
Inrush
V
RTN-VSS
> 12V
V
RTN-VSS
5V/div
V
GATE-VSS
I
INT
I
EXT
5A/div
5A/div
Current limit
TPS2379
www.ti.com SLVSB98 –MARCH 2012
Figure 24. Response to PD Output Short Circuit with AUX MOSFET
The PD control has a thermal sensor that protects the internal hotswap MOSFET. Conditions like startup or
operation into a V
DD
-to-RTN short cause high power dissipation in the MOSFET. An over-temperature shutdown
(OTSD) turns off the hotswap MOSFET and class regulator, which are restarted after the device cools. The
hotswap MOSFET will be re-enabled with the inrush current limit when exiting from an over-temperature event.
Pulling DEN to V
SS
during powered operation causes the internal hotswap MOSFET to turn off.
The hotswap switch will be forced off under the following conditions:
1. V
(DEN –VSS)
< V
PD_DIS
when V
VDD
– V
VSS
is in the operational range,
2. PD is over-temperature, or
3. V
(DEN – VSS)
PoE UVLO falling threshold (~32 V).
CDB and T2P
CDB (converter disable) is an active-low pin that indicates when the internal hotswap MOSFET is inrush limiting.
CDB de-asserts when inrush is over and can be used to enable a downstream converter to start up. Common
interfaces to the converter controller include the soft start or enable pins.
T2P (type 2 PSE) is an active-low multifunction pin that indicates if (PSE = Type_2) and (PD current limit ≠
Inrush).
The usage of T2P is demonstrated in Figure 27. When PSE applies and PD observes a type 2 hardware
classification, T2P pin is pulled to RTN as a indication of the type of PSE.
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