NCP1095GEVB
4
Auxiliary Supply
The NCP1095GEVB supports drawing power from an
alternate or local power source in applications connected to
non-PoE enabled networks. A rear auxiliary supply can be
inserted in connector J6 labeled “P IN”.
The recommended voltage of the auxiliary supply is 24 V.
Table 3. ELECTRICAL CHARACTERISTICS
Operating Range
Auxiliary Input Voltage
20
−
30 V
Auxiliary Input Current
0–5 A
Auxiliary Input Voltage,
Extended
[Warning!]
10–57 V
If an auxiliary supply that is too low (10.1 V
…
20 V) is
inserted before the UVLO threshold was crossed by the PSE,
the class driver could become unintentionally activated.
Therefore it is recommended to adapt the AUX resistor
divider to R
22
= 33 k
W
and R
23
= 15 k
W
for operation with
a low voltage auxiliary supply voltage
.
The NCP1095GEVB is able to operate with an auxiliary
supply voltage up to 57 V. However the customer must take
caution when using a high voltage (>30 V) auxiliary supply:
the NCP1095GEVB has to be unpowered when this high
voltage (30 V
…
57 V) supply is inserted.
Do not insert a high voltage (>30 V) auxiliary supply
when the NCP1095GEVB is already powered by a PSE.
Violating the warning above may result in the PD sourcing
power on the “PoE IN” Ethernet connector.
Figure 3. Operational NCP1095GEVB Showing
Basic Interconnections
G3
G2
BC846BPDW1
162K
IN1
IN2
G4
G1
MMBZ27VALT1G
BC846BPDW1
G3
If the customer needs to implement a system in which
a high voltage (>30 V) rear auxiliary supply can be inserted
while the PD is already powered by the PSE, both
GreenBridge2 rectifiers (U1 and U3) need a gate drive
circuit allowing them to be disabled. Figure 4 shows a gate
drive circuit (GDC) able to turn off the GreenBridge2
internal top MOSFETs.
Figure 4. Basic GreenBridge2 GDC with disable
G4
G3
G1
G2
IN1
IN2
BC846BPDW1
DF6A6.8FUT1G
NCP1095_GBR
½
BAV70LT1G
1.5M
BC846BPDW1
1.5M
If the AUX input pin of NCP1095 is pulled high, it will
immediately drive the GBR pin low. The above gate drive
circuit controlled by the GBR pin makes sure the PD does
not source power under any circumstance in combination
with a high voltage (>30 V) auxiliary supply.
The gate drive circuit shown in Figure 4 is NOT
implemented on NCP1095GEVB. Therefore a high voltage
(>30 V) auxiliary supply should not be inserted when
NCP1095GEVB is already powered by a PSE.
