Acting as an interface between the Power Source
Equipment (PSE) and the Powered Device (PD),
the TPS2371 performs all detection, classification,
inrush current limiting, and switch FET
control that is necessary for compatibility with
Legacy/IEEE 802.3af Standard. The TPS2371
incorporates precision UVLO thresholds and
hysteresis as well as a UVLO off-time delay to
enable Legacy IEEE802.3af PoE compatibilty. An
internal 0.3- FET provides maximum power
delivery. As an additional feature, the TPS2371
interfaces with the enable/soft-start signal of a
dc-to-dc converter, eliminating the need to have
an accurate UVLO in the dc-to-dc converter.
At low input voltages (1.8 V to 10 V), the TPS2371
draws less than 12 µA, allowing accurate sensing
of the external 24.9-k discovery resistor. At input
voltages between 15 V and 20 V, an external
resistor sets the level of current to be drawn during
classification mode. TPS2371 is compatible with
current as well as voltage measurement schemes
for classification. Above 20-V input, the
classification current is shut off, reducing internal
power dissipation.
The TPS2371 drives an internal low-side FET for control of the return side of the power path. The internal FET
is turned on when the input voltage reaches 36 V and above. When the input voltage decreases, the FET
remains on until the input voltage drops to below 30 V.
During initial turn-on of the switch (inrush mode), an external resistor is used to program the inrush current,
allowing a wide range of capacitor values to be used at the load. According to IEEE 802.3af specification, inrush
current of 400 mA is allowed only for 50 ms, limiting the load capacitor to approximately 180 µF. A programmable
inrush current limit removes this limitation, allowing a larger capacitor to be used with a lower inrush current limit.
Acting as an interface between the Power Source
Equipment (PSE) and the Powered Device (PD),
the TPS2371 performs all detection, classification,
inrush current limiting, and switch FET
control that is necessary for compatibility with
Legacy/IEEE 802.3af Standard. The TPS2371
incorporates precision UVLO thresholds and
hysteresis as well as a UVLO off-time delay to
enable Legacy IEEE802.3af PoE compatibilty. An
internal 0.3- FET provides maximum power
delivery. As an additional feature, the TPS2371
interfaces with the enable/soft-start signal of a
dc-to-dc converter, eliminating the need to have
an accurate UVLO in the dc-to-dc converter.
At low input voltages (1.8 V to 10 V), the TPS2371
draws less than 12 µA, allowing accurate sensing
of the external 24.9-k discovery resistor. At input
voltages between 15 V and 20 V, an external
resistor sets the level of current to be drawn during
classification mode. TPS2371 is compatible with
current as well as voltage measurement schemes
for classification. Above 20-V input, the
classification current is shut off, reducing internal
power dissipation.
The TPS2371 drives an internal low-side FET for control of the return side of the power path. The internal FET
is turned on when the input voltage reaches 36 V and above. When the input voltage decreases, the FET
remains on until the input voltage drops to below 30 V.
During initial turn-on of the switch (inrush mode), an external resistor is used to program the inrush current,
allowing a wide range of capacitor values to be used at the load. According to IEEE 802.3af specification, inrush
current of 400 mA is allowed only for 50 ms, limiting the load capacitor to approximately 180 µF. A programmable
inrush current limit removes this limitation, allowing a larger capacitor to be used with a lower inrush current limit.