NCP1095GEVB
2
Assigned Power
The NCP1095GEVB will request Class 8 during Physical
Layer classification. PDs need to take into account that they
can be underpowered and eventually be assigned to Class 3,
4 or 6.
The state of the NCM and NCL outputs provides
information about the power level that the PSE has assigned
to the NCP1095GEVB during classification. See Table 1 to
determine the assigned power based on the status of the
orange NCM and NCL leds.
Table 1. CLASSIFICATION RESULT
NCM
Led
NCL
Led
Assigned
Class
Assigned
Power
off
off
3
13 W
off
on
4
25.5 W
on
off
6
51 W
on
on
8
71.3
…
90 W
PDs assigned to Class 8 may consume greater than 71.3 W
as long as they guarantee not to exceed the 90 W power limit
at the PSE power interface. Operation beyond 71.3 W is,
however, only possible if additional information is available
to the PD regarding the actual link section DC resistance
between the PSE and the PD.
The application should always operate at or below the
assigned power limit. Failure to do so will result in the PSE
disconnecting the PD!
PSE Categorization
The state of the LCF output provides information
(retrieved during classification) about the type of PSE the
NCP1095GEVB is connected to. See Table 2 to determine
the PSE Type based on the status of the red LCF led.
Table 2. PSE TYPE
LCF Led
PSE Categorization
off
The PSE is categorized according to 802.3af/at
(PSE Type 1 or Type 2)
on
The PSE is categorized according to 802.3bt
(PSE Type 3 or Type 4)
The PSE Type determines the MPS timing. It also
indicates to a PD requesting Autoclass whether it makes
sense to go to the maximum power state according to its
assigned Class.
System Startup
A PD can be underpowered and assigned to Class 3 only.
Therefore the DC/DC converter behind NCP1095GEVB
should not draw more than 13 W during start-up. Eventually
the soft-start setting of the DC/DC converter might need to
be adapted to accomplish this.
Requested Power
As mentioned before, the NCP1095GEVB will request
Class 8 during Physical Layer classification. If a lower Class
or power level is preferred, resistor R8 labeled “CLB”
and/or resistor R7 labeled “CLA” should be changed. See
the
for the nominal resistance values.
The Class the PD is actually assigned to is always limited
to the requested Class.
Autoclass
The NCP1095GEVB will by default not request
Autoclass during Physical Layer classification. If the PD
should request Autoclass, remove 0E resistor R9 labeled
“acs”.
Maintain Power Signature (MPS)
A PD should draw a minimum amount of current in order
to prevent the PSE from removing power. The load resistor
R15 was added on the bottom side of the board to make sure
the load current is always sufficient and the NCP1095GEVB
remains powered.
Depending on the minimum current the system may draw,
the resistance value of R15 should be increased for the final
design in order not to waste power unnecessarily.
For some systems, the load resistor can even be omitted.
