TPS23753A
SLVS933B –JULY 2009–REVISED JANUARY 2010
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Threshold Voltages
The TPS23753A has a number of internal comparators with hysteresis for stable switching between the various
states as shown in Figure 16. Figure 17 relates the parameters in the Electrical Characteristics section to the
PoE states. The mode labeled idle between classification and operation implies that the DEN, CLS, and RTN
pins are all high impedance.
PD Powered
Idle
Classification
VVDD-VSS
Detection
VUVLO_H
VCL_HYS
VCL_ON
VCU_HYS
VCU_OFF
1.4V
VUVLO_R
Note: Variable names refer to Electrical Characteristic
Table parameters
Figure 17. Threshold Voltages
PoE Startup Sequence
The waveforms of Figure 18 demonstrate detection, classification, and startup from a type 1 PSE. The key
waveforms shown are VVDD-VSS, VRTN-VSS, and IPI. IEEE 802.3at requires a minimum of two detection levels,
however four levels are shown in this example. Four levels guard against misdetection of a device when plugged
in during the detection sequence.
Figure 18. PoE Startup Sequence
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