Texas Instruments TPS23751 Evaluation Module TPS23751EVM-104 TPS23751EVM-104 데이터 시트
제품 코드
TPS23751EVM-104
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42.5
SLVSB97C – JULY 2012 – REVISED JANUARY 2014
Type 2 PSEs are required to do type 1 hardware classification plus a (new) data-layer classification, or an
enhanced type 2 hardware classification. Type 1 PSEs are not required to do hardware or data link layer (DLL)
classification. A type 2 PD must do type 2 hardware classification as well as DLL classification. The PD may
return the default, 13W current-encoded class, or one of four other choices. DLL classification occurs after
power-on and the Ethernet data link has been established.
enhanced type 2 hardware classification. Type 1 PSEs are not required to do hardware or data link layer (DLL)
classification. A type 2 PD must do type 2 hardware classification as well as DLL classification. The PD may
return the default, 13W current-encoded class, or one of four other choices. DLL classification occurs after
power-on and the Ethernet data link has been established.
Once started, the PD must present a Maintain Power Signature (MPS) to assure the PSE that it is still present.
The PSE monitors its output for a valid MPS and turns the port off if it loses the MPS. Loss of the MPS returns
the PSE to the idle state.
The PSE monitors its output for a valid MPS and turns the port off if it loses the MPS. Loss of the MPS returns
the PSE to the idle state.
shows the operational states as a function of PD input voltage. The upper
half is for IEEE 802.3-2008, and the lower half shows specific differences for IEEE 802.3at. The dashed lines in
the lower half indicate these states are the same (e.g., Detect and Class) for both.
the lower half indicate these states are the same (e.g., Detect and Class) for both.
Figure 20. Threshold Voltages
The PD input, typically an RJ-45 eight-lead connector, is referred to as the power interface (PI). PD input
requirements differ from PSE output requirements to account for voltage drops and operating margin. The
standard allots the maximum loss to the cable regardless of the actual installation to simplify implementation.
IEEE 802.3-2008 was designed to run over infrastructure including ISO/IEC 11801 class C (CAT3 per TIA/EIA-
568) that may have had AWG 26 conductors. IEEE 802.3at type 2 cabling power loss allotments and voltage
drops have been adjusted for 12.5
requirements differ from PSE output requirements to account for voltage drops and operating margin. The
standard allots the maximum loss to the cable regardless of the actual installation to simplify implementation.
IEEE 802.3-2008 was designed to run over infrastructure including ISO/IEC 11801 class C (CAT3 per TIA/EIA-
568) that may have had AWG 26 conductors. IEEE 802.3at type 2 cabling power loss allotments and voltage
drops have been adjusted for 12.5
Ω power loops per ISO/IEC11801 class D (CAT5 or higher per TIA/EIA-568,
typically AWG 24 conductors).
shows key operational limits broken out for the two revisions of the
standard.
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